Systemic lupus erythematosus (SLE) is an autoimmune disease predominantly affecting women and often leading to lupus nephritis and kidney damage. Endoplasmic reticulum (ER) stress has been implicated in several forms of kidney disease, but whether ER stress contributes to renal injury in SLE is unknown. To investigate this, a small molecule chaperone, sodium 4-phenylbutyrate (4-PBA), was administered to the New Zealand Black x New Zealand White F 1 hybrid (NZBWF1) mouse model of SLE. In a prevention study, treatment with 4-PBA from 20 weeks of age (prior to the development of renal injury) delayed the onset of albuminuria and significantly reduced additional indices of renal injury compared with vehicle-treated NZBWF1 mice at 36 weeks of age, including collagen deposition, tubular casts, renal cell apoptosis, and blood urea nitrogen (BUN) concentration. To test whether ER stress contributes to the progression of renal injury once albuminuria has developed, mice were monitored for the onset of albuminuria (3+ or ≥300 mg/dl by dipstick measurement of 24-h urine sample) and once established, were either killed (onset group), or underwent 4-PBA or vehicle treatment for 4 weeks. Treatment with 4-PBA blocked the worsening of glomerular injury, reduced the number of dilated or cast-filled tubules, and reduced the number of apoptotic cells compared with vehicle-treated mice. BUN and left ventricle to bodyweight ratio (LV:BW) were also reduced by 4-PBA treatment. Renal expression of the endogenous chaperones, protein disulphide isomerase (PDI), and 78 kDa glucose-regulated protein (GRP78, also known as binding Ig protein (BiP)), were increased in 4-PBA-treated mice. Together, these results suggest a therapeutic potential for agents like 4-PBA in combating renal injury in SLE.

The classification of diabetic nephropathy (DN) as a vascular complication of diabetes makes the possible involvement of histamine, an endogenous amine that is well known for its vasoactive properties, an interesting topic for study. The aim of the present review is to provide an extensive overview of the possible involvement of histamine in the onset and progression of DN. The evidence collected on the role of histamine in kidney function together with its well-known pleiotropic action suggest that this amine may act simultaneously on glomerular hyperfiltration, tubular inflammation, fibrosis development and tubular hypertrophy.

Chronic kidney disease (CKD) is a major and growing public health concern with increasing incidence and prevalence worldwide. The therapeutic potential of stem cell therapy, including mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) holds great promise for treatment of CKD. However, there are significant bottlenecks in the clinical translation due to the reduced number of transplanted cells and the duration of their presence at the site of tissue damage. Bioengineered hydrogels may provide a route of cell delivery to enhance treatment efficacy and optimise the targeting effectiveness while minimising any loss of cell function. In this review, we highlight the advances in stem cell therapy targeting kidney disease and discuss the emerging role of hydrogel delivery systems to fully realise the potential of adult stem cells as a regenerative therapy for CKD in humans. MSCs and EPCs mediate kidney repair through distinct paracrine effects. As a delivery system, hydrogels can prolong these paracrine effects by improving retention at the site of injury and protecting the transplanted cells from the harsh inflammatory microenvironment. We also discuss the features of a hydrogel, which may be tuned to optimise the therapeutic potential of encapsulated stem cells, including cell-adhesive epitopes, material stiffness, nanotopography, modes of gelation and degradation and the inclusion of bioactive molecules. This review concludes with a discussion of the challenges to be met for the widespread clinical use of hydrogel delivery system of stem cell therapy for CKD.

Sodium bicarbonate (NaHCO 3 ) slows the decline in kidney function in patients with chronic kidney disease (CKD), yet the mechanisms mediating this effect remain unclear. The Dahl salt-sensitive (SS) rat develops hypertension and progressive renal injury when fed a high salt diet; however, the effect of alkali loading on kidney injury has never been investigated in this model. We hypothesized that NaHCO 3 protects from the development of renal injury in Dahl salt-sensitive rats via luminal alkalization which limits the formation of tubular casts, which are a prominent pathological feature in this model. To examine this hypothesis, we determined blood pressure and renal injury responses in Dahl SS rats drinking vehicle (0.1 M NaCl) or NaHCO 3 (0.1 M) solutions as well as in Dahl SS rats lacking the voltage-gated proton channel (Hv1). We found that oral NaHCO 3 reduced tubular NH 4 + production, tubular cast formation, and interstitial fibrosis in rats fed a high salt diet for 2 weeks. This effect was independent of changes in blood pressure, glomerular injury, or proteinuria and did not associate with changes in renal inflammatory status. We found that null mutation of Hv1 also limited cast formation in Dahl SS rats independent of proteinuria or glomerular injury. As Hv1 is localized to the luminal membrane of TAL, our data suggest that alkalization of the luminal fluid within this segment limits cast formation in this model. Reduced cast formation, secondary to luminal alkalization within TAL segments may mediate some of the protective effects of alkali loading observed in CKD patients.

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin–angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water–electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

There is an urgent need to identify novel interventions for mitigating the progression of diabetic nephropathy. Diabetic nephropathy is characterized by progressive renal fibrosis, in which tubulointerstitial fibrosis has been shown to be the final common pathway of all forms of chronic progressive renal disease, including diabetic nephropathy. Therefore targeting the possible mechanisms that drive this process may provide novel therapeutics which allow the prevention and potentially retardation of the functional decline in diabetic nephropathy. Recently, the Ca 2+ -activated K + channel K Ca 3.1 (KCa3.1) has been suggested as a potential therapeutic target for nephropathy, based on its ability to regulate Ca 2+ entry into cells and modulate Ca 2+ -signalling processes. In the present review, we focus on the physiological role of K Ca 3.1 in those cells involved in the tubulointerstitial fibrosis, including proximal tubular cells, fibroblasts, inflammatory cells (T-cells and macrophages) and endothelial cells. Collectively these studies support further investigation into K Ca 3.1 as a therapeutic target in diabetic nephropathy.

Integrin-linked kinase predominantly localizes at focal adhesions to regulate actin cytoskeletal dynamics, including cell migration and matrix remodelling. Although recent studies have suggested both physiological and pathophysiological roles of integrin-linked kinase in the cardiovascular and renal system, its involvement in hypertensive organ dysfunctions, such as those that occur in kidney, has not been investigated. In the present issue of Clinical Science , Alique and co-workers have demonstrated that angiotensin II-induced renal inflammatory responses were attenuated in mice with conditional deficiency of integrin-linked kinase, which were associated with suppression of nuclear factor κB activation and reactive oxygen species generation but not hypertension. The significance, potential mechanisms and future direction are presented and discussed in this Commentary.

ILK (integrin-linked kinase) is an intracellular serine/threonine kinase involved in cell-matrix interactions. ILK dysregulation has been described in chronic renal disease and modulates podocyte function and fibrosis, whereas data about its role in inflammation are scarce. AngII (angiotensin II) is a pro-inflammatory cytokine that promotes renal inflammation. AngII blockers are renoprotective and down-regulate ILK in experimental kidney disease, but the involvement of ILK in the actions of AngII in the kidney has not been addressed. Therefore we have investigated whether ILK signalling modulates the kidney response to systemic AngII infusion in wild-type and ILK-conditional knockout mice. In wild-type mice, AngII induced an inflammatory response, characterized by infiltration of monocytes/macrophages and lymphocytes, and up-regulation of pro-inflammatory factors (chemokines, adhesion molecules and cytokines). AngII activated several intracellular signalling mechanisms, such as the NF-κB (nuclear factor κB) transcription factor, Akt and production of ROS (reactive oxygen species). All these responses were prevented in AngII-infused ILK-deficient mice. In vitro studies characterized further the mechanisms regulating the inflammatory response modulated by ILK. In cultured tubular epithelial cells ILK blockade, by siRNA, inhibited AngII-induced NF-κB subunit p65 phosphorylation and its nuclear translocation. Moreover, ILK gene silencing prevented NF-κB-related pro-inflammatory gene up-regulation. The results of the present study demonstrate that ILK plays a key role in the regulation of renal inflammation by modulating the canonical NF-κB pathway, and suggest a potential therapeutic target for inflammatory renal diseases.

Diabetic nephropathy is the leading cause of kidney failure and its increasing prevalence and incidence has imposed global socio-economic stress on healthcare systems worldwide. Although historically considered a metabolic disorder, recent studies have established that inflammatory responses are central to the pathogenesis of diabetic nephropathy. TLRs (Toll-like receptors) are a family of pattern recognition receptors responsible for the initiation of inflammatory and immune responses. The regulation of TLR2 and TLR4 have been implicated in the pathogenesis of various kidney diseases, and emerging evidence shows their involvement in the perpetuation of inflammation in the diabetic kidney. The present review focuses on the relative contributions of TLR2 and TLR4 in recognizing endogenous ligands relevant to diabetic nephropathy and their subsequent activation of NF-κB (nuclear factor κB), which results in the synthesis and secretion of pro-inflammatory cytokines and chemokines. Moreover, we discuss the pro-inflammatory signalling pathways of TLR2 and TLR4, in which their interruption or blockade may prove to be important therapeutic targets, potentially translated into clinical treatments for diabetic nephropathy. Currently, inhibitors to TLR2 and TLR4 are undergoing clinical trials in various inflammatory models of disease, but none in patients with diabetic nephropathy. Given the existing literature, there is a fundamental necessity to undertake trials in patients with diabetic nephropathy with a focus on renal end points.

Nephrin and Neph-family proteins [Neph1–3 (nephrin-like 1–3)] belong to the immunoglobulin superfamily of cell-adhesion receptors and are expressed in the glomerular podocytes. Both nephrin and Neph-family members function in cell adhesion and signalling, and thus regulate the structure and function of podocytes and maintain normal glomerular ultrafiltration. The expression of nephrin and Neph3 is altered in human proteinuric diseases emphasizing the importance of studying the transcriptional regulation of the nephrin and Neph3 genes NPHS1 (nephrosis 1, congenital, Finnish type) and KIRREL2 (kin of IRRE-like 2) respectively. The nephrin and Neph3 genes form a bidirectional gene pair, and they share transcriptional regulatory mechanisms. In the present review, we summarize the current knowledge of the functions of nephrin and Neph-family proteins and transcription factors and agents that control nephrin and Neph3 gene expression.

Mutations in the novel serine/threonine WNK [ W ith N o lysine (= K )] kinases WNK1 and WNK4 cause PHAII (pseudohypoaldosteronism type II or Gordon's syndrome), a rare monogenic syndrome which causes hypertension and hyperkalaemia on a background of a normal glomerular filtration rate. Current animal models for PHAII recapitulate some aspects of the disease phenotype, but give no clues to how rapidly the phenotype emerges or whether it is reversible. To this end we have created an inducible PHAII transgenic animal model that expresses a human disease-causing WNK4 mutation, WNK4 Q565E, under the control of the Tet-On system. Several PHAII inducible transgenic mouse lines were created, each with differing TG (transgene) copy numbers and displaying varying degrees of TG expression (low, medium and high). Each of these transgenic lines demonstrated similar elevations of BP (blood pressure) and plasma potassium after 4 weeks of TG induction. Withdrawal of doxycycline switched off mutant TG expression and the disappearance of the PHAII phenotype. Western blotting of microdissected kidney nephron segments confirmed that expression of the thiazide-sensitive NCC (Na + –Cl − co-transporter) was increased, as expected, in the distal convoluted tubule when transgenic mice were induced with doxycycline. The kidneys of these mice also do not show the morphological changes seen in the previous transgenic model expressing the same mutant form of WNK4. This inducible model shows, for the first time, that in vivo expression of a mutant WNK4 protein is sufficient to cause the rapid and reversible appearance of a PHAII disease phenotype in mice.

Ninety-one years ago insulin was discovered, which was one of the most important medical discoveries in the past century, transforming the lives of millions of diabetic patients. Initially insulin was considered only important for rapid control of blood glucose by its action on a restricted number of tissues; however, it has now become clear that this hormone controls an array of cellular processes in many different tissues. The present review will focus on the role of insulin in the kidney in health and disease.

Nox (NADPH oxidase)-derived ROS (reactive oxygen species) have been implicated in the development of diabetic nephropathy. Of the Nox isoforms in the kidney, Nox4 is important because of its renal abundance. In the present study, we tested the hypothesis that GKT136901, a Nox1/4 inhibitor, prevents the development of nephropathy in db / db (diabetic) mice. Six groups of male mice (8-week-old) were studied: (i) untreated control db / m , (ii) low-dose GKT136901-treated db / m (30 mg/kg of body weight per day), (iii) high-dose GKT136901-treated db / m (90 mg/kg of body weight per day), (iv) untreated db / db ; (v) low dose GKT136901-treated db / db ; and (vi) high-dose GKT136901-treated db / db . GKT136901, in chow, was administered for 16 weeks. db / db mice developed diabetes and nephropathy as evidenced by hyperglycaemia, albuminuria and renal injury (mesangial expansion, tubular dystrophy and glomerulosclerosis). GKT136901 treatment had no effect on plasma glucose or BP (blood pressure) in any of the groups. Plasma and urine TBARSs (thiobarbituric acid-reacting substances) levels, markers of systemic and renal oxidative stress, respectively, were increased in diabetic mice. Renal mRNA expression of Nox4, but not of Nox2, increased, Nox1 was barely detectable in db / db . Expression of the antioxidant enzyme SOD-1 (superoxide dismutase 1) decreased in db / db mice. Renal content of fibronectin, pro-collagen, TGFβ (transforming growth factor β) and VCAM-1 (vascular cell adhesion molecule 1) and phosphorylation of ERK1/2 (extracellular-signal-regulated kinase 1/2) were augmented in db / db kidneys, with no change in p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase). Treatment reduced albuminuria, TBARS and renal ERK1/2 phosphorylation and preserved renal structure in diabetic mice. Our findings suggest a renoprotective effect of the Nox1/4 inhibitor, possibly through reduced oxidative damage and decreased ERK1/2 activation. These phenomena occur independently of improved glucose control, suggesting GKT136901-sensitive targets are involved in complications of diabetes rather than in the disease process.

Ang-(1–7) [angiotensin-(1–7)] is a biologically active heptapeptide component of the RAS (renin–angiotensin system), and is generated in the kidney at relatively high levels, via enzymatic pathways that include ACE2 (angiotensin-converting enzyme 2). The biological effects of Ang-(1–7) in the kidney are primarily mediated by interaction with the G-protein-coupled receptor Mas. However, other complex effects have been described that may involve receptor–receptor interactions with AT 1 (angiotensin II type 1) or AT 2 (angiotensin II type 2) receptors, as well as nuclear receptor binding. In the renal vasculature, Ang-(1–7) has vasodilatory properties and it opposes growth-stimulatory signalling in tubular epithelial cells. In several kidney diseases, including hypertensive and diabetic nephropathy, glomerulonephritis, tubulointerstitial fibrosis, pre-eclampsia and acute kidney injury, a growing body of evidence supports a role for endogenous or exogenous Ang-(1–7) as an antagonist of signalling mediated by AT 1 receptors and thereby as a protector against nephron injury. In certain experimental conditions, Ang-(1–7) appears to paradoxically exacerbate renal injury, suggesting that dose or route of administration, state of activation of the local RAS, cell-specific signalling or non-Mas receptor-mediated pathways may contribute to the deleterious responses. Although Ang-(1–7) has promise as a potential therapeutic agent in humans with kidney disease, further studies are required to delineate its signalling mechanisms in the kidney under physiological and pathophysiological conditions.

Magnesium (Mg 2+ ) balance is tightly regulated by the concerted actions of the intestine, bone and kidneys. This balance can be disturbed by a broad variety of drugs. Diuretics, modulators of the EGFR (epidermal growth factor receptor), proton pump inhibitors, antimicrobials, calcineurin inhibitors and cytostatics may all cause hypomagnesaemia, potentially leading to tetany, seizures and cardiac arrhythmias. Conversely, high doses of Mg 2+ salts, frequently administered as an antacid or a laxative, may lead to hypermagnesaemia causing various cardiovascular and neuromuscular abnormalities. A better understanding of the molecular mechanisms underlying the adverse effects of these medications on Mg 2+ balance will indicate ways of prevention and treatment of these adverse effects and could potentially provide more insight into Mg 2+ homoeostasis.

The present study was undertaken to evaluate the effects of chronic treatment with c -AUCB { cis -4-[4-(3-adamantan-1-ylureido)cyclohexyl-oxy]benzoic acid}, a novel inhibitor of sEH (soluble epoxide hydrolase), which is responsible for the conversion of biologically active EETs (epoxyeicosatrienoic acids) into biologically inactive DHETEs (dihydroxyeicosatrienoic acids), on BP (blood pressure) and myocardial infarct size in male heterozygous TGR (Ren-2 renin transgenic rats) with established hypertension. Normotensive HanSD (Hannover Sprague–Dawley) rats served as controls. Myocardial ischaemia was induced by coronary artery occlusion. Systolic BP was measured in conscious animals by tail plethysmography. c -AUCB was administrated in drinking water. Renal and myocardial concentrations of EETs and DHETEs served as markers of internal production of epoxygenase metabolites. Chronic treatment with c -AUCB, which resulted in significant increases in the availability of biologically active epoxygenase metabolites in TGR (assessed as the ratio of EETs to DHETEs), was accompanied by a significant reduction in BP and a significantly reduced infarct size in TGR as compared with untreated TGR. The cardioprotective action of c -AUCB treatment was completely prevented by acute administration of a selective EETs antagonist [14,15-epoxyeicosa-5( Z )-enoic acid], supporting the notion that the improved cardiac ischaemic tolerance conferred by sEH inhibition is mediated by EETs actions at the cellular level. These findings indicate that chronic inhibition of sEH exhibits antihypertensive and cardioprotective actions in this transgenic model of angiotensin II-dependent hypertension.

MicroRNA research in humans and mammalian model organisms is in a crucial stage of development. Diagnostic and therapeutic values of microRNAs appear promising, but remain to be established. The physiological and pathophysiological significance of microRNAs is generally recognized, but much better understood in some organ systems and disease areas than others. In the present paper, we review several translational studies of microRNAs, including those showing the potential value of therapeutic agents targeting microRNAs and diagnostic or prognostic microRNA markers detectable in body fluids. We discuss the lessons learned and the experience gained from these studies. Several recent studies have begun to explore translational microRNA research in kidney disease and hypertension. Translational research of microRNAs in the kidney faces unique challenges, but provides many opportunities to develop and apply new methods, and to merge complementary basic and clinical approaches.

Sodium retention has been proposed as the cause of hypertension in the LP rat (offspring exposed to a maternal low-protein diet in utero ) model of developmental programming because of increased renal NKCC2 (Na + /K + /2Cl − co-transporter 2) expression. However, we have shown that LP rats excrete more rather than less sodium than controls, leading us to hypothesize that LP rats ingest more salt in order to maintain sodium balance. Rats were fed on either a 9% (low) or 18% (control) protein diet during pregnancy; male and female offspring were studied at 4 weeks of age. LP rats of both sexes held in metabolism cages excreted more sodium and urine than controls. When given water to drink, LP rats drank more and ate more food than controls, hence sodium intake matched excretion. However, when given a choice between saline and water to drink, the total volume of fluid ingested by LP rats fell to control levels, but the volume of saline taken was significantly larger [3.8±0.1 compared with 8.8±1.3 ml/24 h per 100 g of body weight in control and LP rats respectively; P <0.001]. Interestingly food intake also fell to control levels. Total body sodium content and ECF (extracellular fluid) volumes were greater in LP rats. These results show that prenatal programming of renal sodium wasting leads to a compensatory increase in salt appetite in LP rats. We speculate that the need to maintain salt homoeostasis following malnutrition in utero stimulates greater food intake, leading to accelerated growth and raised BP (blood pressure).

Alterations within the RAS (renin–angiotensin system) are pivotal for the development of renal disease. ACE2 (angiotensin-converting enzyme 2) is expressed in the kidney and converts the vasoconstrictor AngII (angiotensin II) into Ang-(1–7), a peptide with vasodilatory and anti-fibrotic actions. Although the expression of ACE2 in the diabetic kidney has been well studied, little is known about its expression in non-diabetic renal disease. In the present study, we assessed ACE2 in rats with acute kidney injury induced by STNx (subtotal nephrectomy). STNx and Control rats received vehicle or ramipril (1 mg·kg −1 of body weight·day −1 ), and renal ACE, ACE2 and mas receptor gene and protein expression were measured 10 days later. STNx rats were characterized by polyuria, proteinuria, hypertension and elevated plasma ACE2 activity (all P <0.01) and plasma Ang-(1–7) ( P <0.05) compared with Control rats. There was increased cortical ACE binding and medullary mas receptor expression ( P <0.05), but reduced cortical and medullary ACE2 activity in the remnant kidney ( P <0.05 and P <0.001 respectively) compared with Control rats. In STNx rats, ramipril reduced blood pressure ( P <0.01), polyuria ( P <0.05) and plasma ACE2 ( P <0.01), increased plasma Ang-(1–7) ( P <0.001), and inhibited renal ACE ( P <0.001). Ramipril increased both cortical and medullary ACE2 activity ( P <0.01), but reduced medullary mas receptor expression ( P <0.05). In conclusion, our results show that ACE2 activity is reduced in kidney injury and that ACE inhibition produced beneficial effects in association with increased renal ACE2 activity. As ACE2 both degrades AngII and generates the vasodilator Ang-(1–7), a decrease in renal ACE2 activity, as observed in the present study, has the potential to contribute to the progression of kidney disease.

CNP (C-type natriuretic peptide) is a vasodilatory peptide produced by vascular endothelium and the human heart with a short half-life. CNP has been identified within the human kidney; however, few results are available on whether the human kidney is a systemic source of CNP. The aim of the present study was to establish whether CNP is secreted by the human kidney and if synthesis is blunted in CHF (chronic heart failure). A total of 20 male subjects (age, 57±2 years; mean±S.E.M.) undergoing CHF assessment ( n =13) or investigation of paroxysmal supraventricular arrhythmia (normal left ventricular function in sinus rhythm during procedure) ( n =7) were recruited. Renal CNP production was determined from concomitant plasma concentrations in the aorta and renal vein. When considering all subjects, a significant step-up in plasma CNP was found from the aorta to renal vein (3.0±0.3 compared with 8.3±2.4 pg/ml respectively; P =0.0045). The mean increase in CNP was 5.3±2.4 pg/ml (range, −0.9 to +45.3 pg/ml). In patients with CHF, the aortic concentration was 3.3±0.4 pg/ml compared with a renal vein concentration of 4.3±0.6 pg/ml ( P =0.11). In those with normal left ventricular function, the respective values were 2.5±0.5 and 15.7±6.0 pg/ml ( P =0.01). In conclusion, CNP is synthesized and secreted into the circulation by the normal human kidney, where it may have paracrine actions. Net renal secretion of CNP appears to be blunted in patients with CHF.

The kidney plays an important role in maintaining the systemic Ca 2+ and Mg 2+ balance. Thus the renal reabsorptive capacity of these cations can be amended to adapt to disturbances in plasma Ca 2+ and Mg 2+ concentrations. The reabsorption of Ca 2+ and Mg 2+ is driven by transport of other electrolytes, sometimes through selective channels and often supported by hormonal stimuli. It is, therefore, not surprising that monogenic disorders affecting such renal processes may impose a shift in, or even completely blunt, the reabsorptive capacity of these divalent cations within the kidney. Accordingly, in Dent's disease, a disorder with defective proximal tubular transport, hypercalciuria is frequently observed. Dysfunctional thick ascending limb transport in Bartter's syndrome, familial hypomagnesaemia with hypercalciuria and nephrocalcinosis, and diseases associated with Ca 2+ -sensing receptor defects, markedly change tubular transport of Ca 2+ and Mg 2+ . In the distal convolutions, several proteins involved in Mg 2+ transport have been identified [TRPM6 (transient receptor potential melastatin 6), proEGF (pro-epidermal growth factor) and FXYD2 (Na + /K + -ATPase γ-subunit)]. In addition, conditions such as Gitelman's syndrome, distal renal tubular acidosis and pseudohypoaldosteronism type II, as well as a mitochondrial defect associated with hypomagnesaemia, all change the renal handling of divalent cations. These hereditary disorders have, in many cases, substantially increased our understanding of the complex transport processes in the kidney and their contribution to the regulation of overall Ca 2+ and Mg 2+ balance.

Prenatally programmed hypertension induced by maternal protein restriction is associated with increased expression of the renal tubular Na + /K + /2Cl − co-transporter (NKCC2) and the Na + /Cl − co-transporter (NCC). This has led to the suggestion that renal Na + retention contributes to the development of hypertension in the LP rat (offspring exposed to a maternal low-protein diet in utero ). However, this hypothesis has not been tested in vivo . Renal clearance measurements in hypertensive 4-week-old male and female LP rats showed that, although the glomerular filtration rate remained unaltered, urine flow ( P <0.01) and urinary Na + excretion rates (1.6±0.3 and 3.0±0.4 μmol·min −1 ·100 g −1 of body weight in control male and LP male respectively; P <0.001) were increased. Na + excretion was positively correlated with mean arterial pressure in both males ( P <0.01) and females ( P <0.05), but neither the slope nor the intercept differed between control and LP rats. Fractional excretion of Na + was increased in male (1.5±0.2 and 3.0±0.5% in control and LP rats respectively; P <0.001) and female LP rats, implying reduced tubular reabsorption of Na + . Western blotting and quantitative PCR showed that NKCC2 expression was increased, whereas NCC mRNA was not up-regulated. Na + /K + ATPase α 1 subunit expression did not differ from controls; however, there was a significant reduction in whole kidney pump activity (23.4±1.8 and 17.7±1.2 nmol of phosphate·μg −1 of protein·h −1 in control male and male LP rats respectively; P <0.001); immunohistochemistry showed that the α 1 subunit was virtually absent from the inner medulla. The greater Na + excretion of LP rats can be explained, in part, by a pressure–natriuresis mechanism; however, the loss of the Na + /K + ATPase α 1 subunit from the inner medulla and up-regulation of NKCC2 suggests that altered renal Na + handling is also programmed prenatally.

In liver cirrhosis, elevated levels of NO and ROS (reactive oxygen species) might greatly favour the generation of peroxynitrite. Peroxynitrite is a highly reactive oxidant and it can potentially alter the vascular reactivity and the function of different organs. In the present study, we evaluated whether peroxynitrite levels are related to the progression of renal vascular and excretory dysfunction during experimental cirrhosis induced by chronic BDL (bile-duct ligation) in rats. Experiments were performed at 7, 15 and 21 days after BDL in rats and in rats 21 days post-BDL chronically treated with L -NAME ( N G -nitro- L -arginine methyl ester). Sodium balance, BP (blood pressure), basal RPP (renal perfusion pressure) and the renal vascular response to PHE (phenylephrine) and ACh (acetylcholine) in isolated perfused kidneys were measured. NO levels were calculated as 24-h urinary excretion of nitrites, ROS as TBARS (thiobarbituric acid-reacting substances), and peroxynitrite formation as the renal expression of nitrotyrosine. BDL rats had progressive sodium retention, and decreased BP, RPP and renal vascular responses to PHE and ACh in the time following BDL. They also had increasing levels of NO and ROS, and renal nitrotyrosine accumulation, especially in the medulla. All of these changes were either prevented or significantly decreased by chronic L -NAME administration. In conclusion, these results suggest that the increasing levels of peroxynitrite might contribute to the altered renal vascular response and sodium retention in the development of the experimental biliary cirrhosis. Moreover, the beneficial effects of decreasing NO synthesis are, at least in part, mediated by anti-peroxinitrite-related effects.

Glucagon, in the setting of absolute or relative insulin deficiency, is thought to contribute to the pathogenesis of hyperglycaemia in diabetes, but much of the evidence is extrapolated from short-term studies to the long-term condition. In the present issue of Clinical Science , Li and co-workers report that infusion of glucagon raised fasting plasma glucose concentrations and impaired glucose tolerance over 4 weeks in mice, thus demonstrating a sustained glycaemic effect of hyperglucagonaemia. Nonetheless, compelling evidence that glucagon contributes to the pathogenesis of hyperglycaemia in diabetes awaits long-term selective reduction of glucagon secretion or action in humans.

Clinical studies have shown that patients with early Type 2 diabetes often have elevated serum glucagon rather than insulin deficiency. Imbalance of insulin and glucagon in favouring the latter may contribute to impaired glucose tolerance, persistent hyperglycaemia, microalbuminuria and glomerular injury. In the present study, we tested the hypothesis that long-term glucagon infusion induces early metabolic and renal phenotypes of Type 2 diabetes in mice by activating glucagon receptors. Five groups of adult male C57BL/6J mice were treated with vehicle, glucagon alone (1 μg/h via an osmotic minipump, intraperitoneally), glucagon plus the glucagon receptor antagonist [Des-His 1 -Glu 9 ]glucagon (5 μg/h via an osmotic minipump), [Des-His 1 -Glu 9 ]glucagon alone or a high glucose load alone (2% glucose in the drinking water) for 4 weeks. Glucagon infusion increased serum glucagon by 129% ( P <0.05), raised systolic BP (blood pressure) by 21 mmHg ( P <0.01), elevated fasting blood glucose by 42% ( P <0.01), impaired glucose tolerance ( P <0.01), increased the kidney weight/body weight ratio ( P <0.05) and 24 h urinary albumin excretion by 108% ( P <0.01) and induced glomerular mesangial expansion and extracellular matrix deposition. These responses were associated with marked increases in phosphorylated ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt signalling proteins in the liver and kidney ( P <0.01). Serum insulin did not increase proportionally. Concurrent administration of [Des-His 1 -Glu 9 ]glucagon with glucagon significantly attenuated glucagon-increased BP, fasting blood glucose, kidney weight/body weight ratio and 24 h urinary albumin excretion. [Des-His 1 -Glu 9 ]glucagon also improved glucagon-inpaired glucose tolerance, increased serum insulin by 56% ( P <0.05) and attenuated glomerular injury. However, [Des-His 1 -Glu 9 ]glucagon or high glucose administration alone did not elevate fasting blood glucose levels, impair glucose tolerance or induce renal injury. These results demonstrate for the first time that long-term hyperglucagonaemia in mice induces early metabolic and renal phenotypes of Type 2 diabetes by activating glucagon receptors. This supports the idea that glucagon receptor blockade may be beneficial in treating insulin resistance and Type 2 diabetic renal complications.

Clinical and experimental studies indicate that the progression of renal disease is faster in males than females. These observations are corroborated by a sexual dimorphism observed in the polygenetic MWF (Munich Wistar Frömter) rat model. The age-dependent spontaneous progression of increased UAE (urinary albumin excretion) in male MWF rats is influenced by multiple QTLs (quantitative trait loci). In contrast, female MWF rats only develop a slight increase in UAE, while the role of genetic factors for this phenotype is unknown. In the present study, we show that, compared with resistant SHRs (spontaneously hypertensive rats), both male and female MWF rats develop a significant increase in UAE at 24 weeks of age ( P <0.0001), although blood pressures were lower compared with SHRs ( P <0.0001). UAE was significantly higher in male (7-fold) compared with female MWF rats (162.6±15.9 compared with 24.0±5.5 mg/24 h respectively; P <0.0001), and only male MWF rats developed significant glomerulosclerosis and tubulointerstitial damage in the kidney ( P <0.0001). To test the role of genetic factors in the development of low grade albuminuria in female MWF rats, we analysed the role of a major UAE QTL on rat chromosome 6. To this end, we analysed a consomic MWF-6 SHR strain in which chromosome 6 from SHRs was introgressed into the MWF rat background. Time course analysis of UAE in females indicated that the small increase in UAE in MWF rats was fully suppressed by exchange of rat chromosome 6. Thus, taken together with previous studies in males, we show that RNO6 protects against the increase in albuminuria with age in both female and male MWF rats.

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE 2 , PGI 2 (prostacyclin), PGD 2 , PGF 2α and TXA 2 (thromboxane A 2 ). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE 2 receptor), IP (PGI 2 receptor), DP (PGD 2 receptor), FP (PGF 2α receptor) and TP (TXA 2 receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.

The α-adducin Gly460Trp polymorphism alters renal sodium transport and is associated with hypertension. Despite the immediate sodium- and volume-depleting effects of aerobic exercise, the influence of the α-adducin Gly460Trp polymorphism on PEH (postexercise hypotension) has not been studied. In the present study we examined the effects of the α-adducin Gly460Trp polymorphism on PEH among 48 men (42.6±1.6 years; mean±S.E.M.) with high BP (blood pressure; 144.0±1.7/84.7±1.1 mmHg). Subjects completed three experiments: non-exercise control and two cycle exercise sessions at 40% (light exercise) and 60% (moderate exercise) of maximal oxygen consumption. Subjects left the laboratory wearing an ambulatory BP monitor. PCR and restriction enzyme digestion determined the genotypes. No subjects had the Trp460Trp genotype due to the low frequency of 5% in the population. Repeated measure ANCOVA tested whether BP differed over time between experimental conditions and genotypes (Gly460Gly, n =36; Gly460Trp, n =12). Among Gly460Gly genotypes, SBP (systolic BP) was reduced by 5.2±1.4 mmHg after moderate exercise compared with non-exercise controls over 9 h ( P <0.01). Among Gly460Trp genotypes, SBP was lowered by 7.8±2.3 mmHg; after light exercise compared with non-exercise controls over 9 h ( P <0.05). The SBP reductions after light exercise (0.6±1.3 compared with 7.8±2.3 mmHg; P <0.05) but not moderate exercise (5.2±1.4 compared with 3.8±2.4 mmHg; P ≥0.05) differed between the Gly460Gly and Gly460Trp genotypes respectively. Men with Gly460Gly had a reduced SBP after moderate exercise, whereas men with Gly460Trp had a reduced SBP after light exercise. However, only the SBP reductions after light exercise differed between genotypes. Our findings indicate that the α-adducin Gly460Trp genotype may be useful in identifying men who have a reduced BP after lower intensity aerobic exercise.

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport, vascular smooth muscle contractility and production of reactive oxygen species and by interacting with the renin–angiotensin and sympathetic nervous systems. Dopamine receptors are classified into D 1 -like (D 1 and D 5 ) and D 2 -like (D 2 , D 3 and D 4 ) subtypes based on their structure and pharmacology. Each of the dopamine receptor subtypes participates in the regulation of blood pressure by mechanisms specific for the subtype. Some receptors regulate blood pressure by influencing the central and/or peripheral nervous system; others influence epithelial transport and regulate the secretion and receptors of several humoral agents. This review summarizes the physiology of the different dopamine receptors in the regulation of blood pressure, and the relationship between dopamine receptor subtypes and hypertension.

Low BP (blood pressure) is a recognized risk factor for some patients with NPG (normal pressure glaucoma). We have shown previously that patients with orthostasis have impaired circadian renal handling of sodium, which may contribute to the low BP. Therefore the aim of the present study was to examine the renal handling of sodium, the circadian variations in BP and the neurohormonal response to an orthostatic test in a selected subpopulation of 18 patients with NPG with vasospastic and orthostatic symptoms, and in 24 healthy control subjects. The variations in BP and renal tubular sodium handling were evaluated using 24 h ambulatory BP recordings, 24 h urine collections and determination of endogenous lithium clearance as a marker of proximal sodium reabsorption. The neurohormonal and BP responses to changes in posture were also determined in a 30 min orthostatic test. This selected group of patients with NPG had lower 24 h ambulatory BPs ( P <0.001), and a more pronounced fall in BP when assuming an upright position ( P <0.001) compared with controls. FE Li (fractional excretion of lithium) was higher in patients with NPG than controls during the day (36.6±21.8 compared with 20.4±8.7% respectively; P <0.01; values are means±S.D.) as well as during the night (38.8±41.9 compared with 19.7±10.8% respectively; P <0.02), suggesting a reduced reabsorption of sodium in the proximal tubule. This was compensated for by an increased distal reabsorption of sodium in patients with NPG ( P <0.01). These data demonstrate that patients with vasospastic NPG have a high excretion of lithium, suggesting reduced sodium reabsorption in the proximal tubule, in spite of a low BP. The abnormal renal sodium handling might contribute to the maintenance of arterial hypotension and progression of the optic nerve damage in these patients.

The peptide AM (adrenomedullin) is stimulated by hypoxia through HIF-1 (hypoxia-inducible factor-1). The majority of human CC-RCCs (clear cell renal cell carcinomas) display mutations in the tumour suppressor protein von Hippel–Lindau, which leads to constitutively elevated HIF-1. We hypothesized that AM is increased in CC-RCC tumours and that AM is a plasma biomarker for CC-RCC. Tumours and non-malignant kidney tissue were obtained from patients that underwent unilateral nephrectomy. Blood samples were drawn at the day of surgery, 3–6 days after surgery and 4–5 weeks after surgery. AM mRNA and peptide expression in tissue and AM plasma concentration were determined. HIF-1α was localized in tissue by immunohistochemistry. AM mRNA was elevated in CC-RCC compared with adjacent renal cortex (6-fold, n =18; P <0.02). There was no difference in AM mRNA between cortex and non-CC-RCC tissue ( n =7). AM peptide concentration was elevated in CC-RCC tissue compared with adjacent cortex (4-fold, n =6; P <0.02), whereas there was no difference between cortex and non-CC-RCC tissue ( n =5). HIF-1α immunoreactivity was detected in the majority of cell nuclei in 76% of CC-RCC, consistent with constitutive stabilization. In non-CC-RCC, HIF-1α staining was focal. Before surgery there was no difference in plasma AM concentration between tumour types. Nephrectomy increased plasma AM significantly after 3–6 days and a similar pre-surgery level was observed after 4–5 weeks in both groups of tumour patients. We conclude that elevated tissue AM is a distinguishing feature of CC-RCC compared with other kidney tumours. Plasma AM is not suited as a tumour marker for this disease.

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Successful gene therapy requires gene delivery that is efficient, has an optimal route of administration and has biosafety. The aims of the present study were to evaluate the safety and applicability of the subcutaneous delivery route for adenoviral transgenes containing the human β 2 -adrenoceptor (adeno-β 2 -AR) and to investigate whether this approach prevented renal dysfunction in a rat model of endotoxaemic shock induced by LPS (lipopolysaccharide). Subcutaneous administration of adeno-β 2 -AR (a total of 10 10 viral particles) significantly increased β-AR density in the kidney, lung and liver, but was without effect on physiological and plasma biochemical parameters. Moreover, this dose of virus did not cause any of the potential toxic responses of viral administration, such as inflammation and tissue TNF (tumour necrosis factor)-α expression. Although the LPS challenge caused a decrease in glomerular filtration rate, fractional excretion of sodium and renal β-AR density in all groups, the reduction in renal function was significantly less in the rats given adeno-β 2 -AR compared with non-treated rats. Thus, although further evaluation will be required, this initial study demonstrated that the subcutaneous injection of adeno-β 2 -AR was efficient, comparatively non-pathogenic and potentially therapeutic to deal with acute renal failure associated with sepsis.

Uncertainties exist over the glomerular filtration of aluminium and virtually nothing is known about its segmental handling along the nephron. The present study has used micropuncture, combined with electrothermal atomic absorption spectroscopy, to determine directly the aluminium content of glomerular filtrate and of late PCTs (proximal convoluted tubules) and early distal tubules in anaesthetized Munich–Wistar rats infused with three different doses of aluminium citrate (plasma aluminium concentrations, 2.9±0.1, 5.2±0.4 and 10.0±0.9 μg·ml −1 respectively). Aluminium filtration into Bowman's space was found to be considerably greater than that predicted by an in vitro filtration system: in all three groups it was essentially filtered freely. No significant aluminium reabsorption took place along the PCT, but with every dose the FD Al (fractional delivery of aluminium; tubular fluid:plasma aluminium/inulin concentration ratio) was lower at the early distal site than at the late PCT ( P <0.001 in each case), indicating net aluminium reabsorption in the loop of Henle. This reabsorption amounted to 19–26% of the filtered aluminium load. In the low- and medium-dose groups, there was no significant difference between FD Al at the early distal site and that in the final urine; however, in the high-dose group, FD Al in the urine (1.02±0.06) exceeded that at the early distal tubule (0.75±0.04; P <0.001), suggesting aluminium secretion in the distal nephron. The results indicate that aluminium loads, when complexed with citrate, are excreted efficiently owing to a combination of glomerular filtration and minimal reabsorption.

Stereological structural alterations of the heart and kidney were studied in four groups ( n =5) of spontaneously hypertensive rats (SHRs) treated for 30 days: (i) control, (ii) N G -nitro- L -arginine methyl ester [ L -NAME; nitric oxide (NO) synthesis inhibitor] alone, (iii) enalapril alone and (iv) L -NAME plus enalapril. Blood pressure (BP) was elevated significantly in NO-deficient SHRs (rats receiving L -NAME) or significantly lower in enalapril-treated SHRs. Co-administration of L -NAME and enalapril caused a 20% decrease in BP compared with untreated SHRs. NO-deficient SHRs had a decrease in body mass, but this loss of body mass was prevented efficiently in the enalapril-treated group. Enalapril treatment decreased the left ventricular (LV) mass index in SHRs, even in animals with NO synthesis blocked. NO deficiency in SHRs caused a larger decrease in the number of LV cardiomyocyte nuclei, which had a negative correlation with both LV mass index and BP. The volume-weighted glomerular volume (VWGV) separated the SHRs into two groupings: (i) control and NO-deficient SHRs, and (ii) enalapril- and L -NAME plus enalapril-treated SHRs. There was a significant difference between these two groupings, with VWGV being more than 15% smaller in the latter compared with the former grouping. The present findings reinforce the evidence that enalapril efficiently treats genetic hypertension, and demonstrate that this effect is observed even when NO synthesis is inhibited. Enalapril administration also decreases cardiac and renal structural damage caused by genetic hypertension, as well as by the interaction between genetic hypertension and NO deficiency.

In the present in vivo study, we have investigated whether inhibitors of the Na + /Mg 2+ exchanger quinidine and imipramine influence the development of hypertension and whether this is associated with modulation of mitogen-activated protein (MAP) kinase activation in arteries and kidneys of hypertensive rats. Sprague—Dawley rats were divided into four groups ( n =6/group): control (vehicle), angiotensin II (Ang II; 150 ng/kg of body weight per min subcutaneously), quinidine [Ang II (150 ng/kg of body weight per min)+quinidine (5 mg/kg of body weight per day in food)] and imipramine groups [Ang II (150 ng/kg of body weight per min)+imipramine (5 mg/kg/day in food)]. Rats were studied for 3 weeks. Phosphorylation of vascular and renal extracellular-signal-regulated protein kinase 1/2 (ERK1/2), p38MAP kinase and c-Jun N-terminal kinase (JNK) were assessed using phospho-specific antibodies. Ang II increased systolic blood pressure from 112±5 mmHg to 215±9 mmHg ( P <0.01). Development of hypertension was attenuated in Ang II-infused rats treated with quinidine (173±6 mmHg) and imipramine (152±6 mmHg) ( P <0.01). Phosphorylation of ERK1/2, p38MAP kinase and JNK, which were increased 2–3-fold in arteries of the Ang II group, were reduced by quinidine and imipramine ( P <0.05). Activation of renal MAP kinases was also increased in the Ang II group ( P <0.05). Quinidine and imipramine reduced the phosphorylation of renal ERK1/2, but did not modify renal p38MAP kinase or JNK. Our data demonstrate that Ang II induces severe hypertension in Sprague—Dawley rats and this is associated with increased phosphorylation of vascular and renal MAP kinases. Quinidine and imipramine attenuated the development of hypertension and normalized MAP kinase activity. The findings from this study suggest a possible role for the Na + /Mg 2+ exchanger in vascular signalling events associated with blood pressure elevation in Ang II-dependent hypertension.

Recent studies have proposed a link between impaired nephrogenesis, decreased activity of the renin–angiotensin system and the onset of hypertension in rats exposed in the uterus to a maternal low-protein diet. However, there is no detailed information about renal function in this model; hence the aim of the present study was to assess renal function in young (4-week-old) rats exposed in the uterus to a maternal low-protein diet. Pregnant Wistar rats were fed isocalorific diets containing either 18% (normal protein; offspring denoted NP rats) or 9% (low protein; offspring denoted LP rats) (w/w) protein from conception until birth. At 4 weeks of age, male offspring were anaesthetized and prepared for the study of renal function, during which animals received saline alone, a bolus of enalapril (5 mg·kg -1 ) or a bolus of enalapril followed by an infusion of angiotensin II (30 ng·min -1 ·kg -1 ). Under control conditions, renal haemodynamic and tubular function did not differ. However, when challenged with angiotensin II, LP rats responded with a greater decrease in glomerular filtration rate than did NP rats [NP, 2.0±0.2 ml·min -1 ·g -1 kidney weight ( n =9); LP, 1.0±0.2 ml·min -1 ·g -1 kidney weight ( n =5); P <0.05]. Renal electrolyte excretion did not differ. LP rats had significantly fewer glomeruli than NP rats ( P <0.01). Renal angiotensin II AT 1 receptor expression was increased ( P <0.01) by 24% in LP rats. It is concluded that blood pressure may be elevated in LP rats in order to maintain glomerular filtration rate against a background of fewer nephrons. Increased AT 1 receptor expression, which may arise as a result of the direct effect of protein restriction or in response to the reported decrease in renal tissue angiotensin II concentration, could also contribute to the elevated blood pressure of this model.

Transgenic overexpression of erythropoietin (Epo) in mice increases haematocrit to a mean of 80% in adult mice, leading to an increase in blood viscosity and volume. As a consequence, renal tissue endothelin-1 (ET-1) concentrations are significantly elevated in erythropoietin-overexpressing (Epo+) mice (mean±S.E.M; Epo+, 798±71; Epo-, 400±25pg/g tissue; P <0.01). To investigate the pattern of expression of the primary translation product of the ET-1 gene, prepro-ET-1, in kidneys of (Epo+) mice, we generated crossbred mice overexpressing the human EPO gene with mice carrying a reporter gene construct expressing the LacZ gene under the control of the human prepro-ET-1 promotor sequence (LacZ+/Epo+). For comparison, we generated (LacZ+/Epo-) mice from the same strains. After Bluo-Gal staining of frozen kidney sections ( n = 10 in each group), intracellular blue precipitates as indicators of prepro-ET-1 promotor activity were detectable in tubular and vascular endothelium and glomerular cells in (LacZ+/Epo-) as well as (LacZ+/Epo+) mice. Comparison of the amount of blue precipitates by semiquantitative scoring showed a significant increase in reporter gene activity in tubular epithelium of (LacZ+/Epo+) mice (mean±S.E.M.; LacZ+/Epo+, 1.64±0.18; LacZ+/Epo-, 1.00±0.19; P <0.05). Reporter gene activity was not significantly elevated in epithelium of small intrarenal arteries of (LacZ+/Epo+) mice (mean±S.E.M.; LacZ+/Epo+, 0.86±0.14; LacZ+/Epo-, 0.38±0.21; P = 0.08) and was similar in glomerular cells (mean±S.E.M.; LacZ+/Epo+, 1.28±0.16; LacZ+/Epo-, 1.14±0.21; P = 0.6). The main source of elevated ET-1 tissue concentration in kidneys of (Epo+) mice therefore seems more likely to be tubular than vascular endothelium or glomerular cells.

Endothelin (ET)-converting enzyme (ECE) is a rate-limiting step in ET-1 generation, and its expression and activity are increased significantly with the development of congestive heart failure (CHF). The selective enzymic inhibition of ET-1 formation thus seems to be a very important target in the prevention of CHF. We evaluated the chronic effects of a specific ECE inhibitor, FR901533 (0.3mg·kg -1 ·h -1 , n = 5) on cardiac, hormonal, and body fluid balance in dogs with CHF induced by rapid right ventricular pacing (270beats/min, 22 days). Vehicle dogs were given placebo ( n = 5). Despite no significant difference in blood pressure, FR901533 decreased pulmonary capillary wedge pressure and increased cardiac output compared with the vehicle. FR901533 prevented the reduction of urine flow rate and urinary sodium excretion in association with an increase in the glomerular filtration rate and renal plasma flow compared with the vehicle. FR901533 also suppressed significantly the elevation of plasma atrial natriuretic peptide and aldosterone levels which is an established prognostic factor in CHF. These results indicate that the role of ECE in CHF is important and that chronic ECE inhibition could possess therapeutic potential in the treatment of CHF not only on haemodynamics but also in the prevention of fluid retention.

Aldosterone-induced hypertension is associated with renal damage that may be mediated by endothelin-1 (ET-1). We evaluated whether inflammatory cell infiltration and DNA-binding activity of the transcription factors nuclear factor κB (NF-κB) and activator protein-1 (AP-1) were increased in kidneys from aldosterone-infused rats. The role of ET-1 in these processes was evaluated by treating rats with the ET A -receptor blocker, BMS 182874. Rats were infused with aldosterone (0.75 µ g/h) via a mini-osmotic pump and were given 1% NaCl in the drinking water in the absence and presence of BMS 182874 or of the aldosterone receptor blocker, spironolactone. Renal sections were used to assess inflammatory cell infiltration, which was identified immunocytochemically using monoclonal antibodies against macrophages (ED1+). Electrophoretic mobility shift assays evaluated the DNA-binding activity of NF-κB and AP-1 in renal tissue. Systolic blood pressure (BP) was increased in the aldosterone-infused group compared with controls (123±6 versus 110±10mmHg, P <0.05). BMS 182874 and spironolactone significantly decreased BP ( P <0.05). Macrophage infiltration was increased in the kidneys of aldosterone-infused rats compared with controls. Renal binding activity (arbitrary units) of AP-1, in contrast with that of NF-κB, increased in aldosterone-infused rats compared with control rats (AP-1, 4.2±0.3 versus 1.0±0.1, P <0.05; NF-κB, 1.6±0.5 versus 1.2±0.5). BMS 182874 and spironolactone decreased macrophage infiltration (by 70% and 50% respectively) and AP-1 binding activity (1.0±0.3 and 0.8±0.3 respectively). In conclusion, kidneys from aldosterone-infused rats exhibited macrophage infiltration and increased AP-1 DNA-binding activity. These processes were attenuated by BMS 182874. Our findings suggest that renal damage in aldosterone-dependent hypertension is associated with inflammatory processes that are mediated in part via ET-1.

Endothelin-1 (ET-1) and atrial natriuretic peptide (ANP) play important roles in the regulation of body fluid balance in congestive heart failure (CHF). Renal production of ET-1 increases in CHF and it is a significant independent predictor of sodium excretion. ANP inhibits the ET system through cGMP, a second messenger of ANP. However, in severe CHF, plasma cGMP levels reached a plateau despite the activation of ANP secretion. Thus, ANP does not seem to sufficiently oppose exaggerated ET-1 actions in severe CHF, partially due to the accelerated degradation of cGMP, through phosphodiesterase type 5 (PDE5). We examined the chronic effects of a PDE5 inhibitor, T-1032 (1mg/kg per day, n = 5), on renal function and renal production of ET-1 in dogs with CHF induced by rapid ventricular pacing (270beats/min). Vehicle dogs were given a placebo ( n = 5) and normal dogs ( n = 5) served as normal controls without pacing. In this experimentally produced CHF, plasma levels of ET-1, ANP and cGMP were elevated and renal production of cGMP was increased compared with the normal group, associated with increases in renal expression of preproET-1 mRNA and the number of ET-1-positive cells in glomeruli. In the T-1032 group, systemic and renal production of cGMP were further increased compared with the vehicle group despite no significant difference in plasma ANP levels between the two groups. Subsequently, the agent significantly improved urine flow rate, sodium excretion rate and glomerular filtration rate (GFR) associated with reductions in renal expression of preproET-1 mRNA and the number of ET-1-positive cells compared with the vehicle group. Moreover, there was a significant negative correlation between the number of ET-1-positive cells and GFR ( r =-0.802 and P <0.001 respectively). Our results indicate that chronic PDE5 inhibition ameliorates the antagonistic relationship between renal ANP and ET-1 through the cGMP pathway, subsequently preventing renal dysfunction during the progression of CHF.

Potassium channels are ubiquitous, being present in all living organisms. These proteins share common structural elements, which confer common functional features. In general, all K + channels have a high selectivity for K + , and are blocked by cations of similar dimensions, such as Cs + and Ba 2+ . Mutations in the pore region tend to lead to either the total loss of function or K + selectivity. We have made mutations to one of the most highly conserved residues of the pore, glycine-143, of the inward rectifier ROMK1 (Kir1.1), and examined the resulting channel properties in the Xenopus oocyte expression system with a two-electrode voltage clamp. Mutations G143A and G143R resulted in failure to express functional channels. Co-injection of wild-type ROMK1 cRNA with these mutants led to rescue of channel function, which was different from wild-type ROMK1. In both mutants, the sensitivity to Ba 2+ and Cs + was increased, the rate of onset of block by Ba 2+ was enhanced, and the selectivity to potassium was reduced. Whereas the crystallographic evidence shows that cations bind to the carbonyl backbone of the pore-lining residues, the present results indicate that the side chains of these amino acids, which face away from the pore lining, also affect permeation.

Adrenomedullin is a vasodilator peptide produced in various organs, including heart and kidney. A novel adrenomedullin receptor complex has recently been identified, namely the calcitonin receptor-like receptor (CRLR) and receptor-activity modifying protein (RAMP) 2. In the present study, we have examined gene expression of RAMP2, CRLR and adrenomedullin in hearts and kidneys of rats with congestive heart failure caused by coronary artery ligation. Partial cloning was performed to determine the rat RAMP2 nucleotide sequence. Messenger RNA levels were then determined using competitive, quantitative reverse transcription-PCR techniques. Significantly increased expression levels (means±S.E.) of RAMP2, CRLR and adrenomedullin mRNA were found in the atrium (1.8±0.2-fold, 1.8±0.2-fold and 2.1±0.1-fold, respectively, compared with sham operated rats) and in the ventricle (1.4±0.1-fold, 1.3±0.03-fold and 3.0±0.5-fold respectively). On the other hand, expression levels of RAMP2, CRLR and adrenomedullin mRNAs were not significantly changed in the kidney. These findings suggest potential roles of locally-produced and locally-acting adrenomedullin in the failing heart.

A side-effect of the immunosuppressive drug FK506 (Prograf; tacrolimus) is hypomagnesaemia. We have investigated the effects of short-term (7-day) treatment of rats with FK506, using a protocol designed to indicate whether there are modifications in the renal tubular handling of magnesium and other electrolytes, or in the tissue deposition of magnesium, which may account for the hypomagnesaemia. We have also investigated whether parathyroid hormone has a role in the observed hypomagnesaemia. Two studies have been performed; in the first we administered FK506 (0.5 mgċkg -1 body weightċday -1 ) or vehicle by intraperitoneal injection for 7 days, and then housed the rats in metabolic cages for the 24 h collection of urine. At the end of the metabolic cage period, the animals were anaesthetized, and blood and tissue samples were taken for analysis. In the second set of experiments the dosage regime was identical, but at the end of the treatment period the animals were anaesthetized for implantation of arterial and venous cannulae, and then received a saline (plus inulin) infusion for 6 h, during which time blood and urine samples were collected. The dose of FK506 employed did not decrease the glomerular filtration rate. FK506 elicited hypomagnesaemia in both sets of experiments, accompanied by inappropriately high fractional excretion of magnesium. There was also evidence of disruption of the normal renal reabsorption of calcium, but this did not result in hypocalcaemia. Plasma parathyroid hormone activity was not significantly different between the two groups, and there was no evidence of altered tissue content of magnesium in kidney, liver, heart, skeletal muscle or bone. The study confirms that hypomagnesaemia is a significant side-effect of FK506, even at a relatively low dose which did not decrease the glomerular filtration rate. The effect is not due to a decrease in parathyroid hormone release, or to translocation of magnesium from plasma to tissues, but does reflect decreased renal tubular magnesium (and calcium) reabsorption.

In the present study we have characterized the evolution of changes in systemic haemodynamics (thermodilution in conscious animals) and sodium balance (metabolic cages) in a model of liver cirrhosis induced by chronic bile duct ligation (BDL). Mean arterial pressure (BDL, 111.5±4.7 mmHg; sham-operated, 122.9±3.0 mmHg) and peripheral vascular resistance (BDL, 2.63±0.08 units; sham-operated, 2.93±0.09 units) were lower in BDL rats from day 12 after surgery and decreased progressively throughout the following days. Portal hypertension was evident earlier in BDL rats and was maintained throughout the study period. Cardiac index (BDL, 58.8±3.9 ml·min -1 ·100 g -1 ; sham-operated, 43.9±1.5 ml·min -1 ·100 g -1 ) and stroke volume (BDL, 147.2±12.7 ml·beat -1 ·100 g -1 ; sham-operated, 109.0±4.2 ml·beat -1 ·100 g -1 ) were significantly elevated in the BDL rats only from day 18 after surgery. There were no significant differences in sodium balance between the groups until day 16 after surgery, at which time BDL animals started to retain significantly more sodium than the controls. Sodium retention increased progressively, and at day 20 BDL rats had retained 0.7 mmol/100 g more than the control animals (accumulated retention: BDL, 2.2±0.2 mmol/100 g; sham-operated, 1.5±0.2 mmol/100 g). Plasma renin activity and aldosterone concentration were not elevated in the BDL animals at days 12, 16 or 20 after surgery. These data indicate that the BDL rat model shows early portal hypertension, peripheral vasodilation and arterial hypotension, several days before sodium retention is detectable, and in the absence of changes in plasma levels of renin and aldosterone. Overall, these data suggest that, in the BDL rat model, sodium retention is secondary to portal hypertension and peripheral vasodilation.

Nabumetone, a newer non-steroidal anti-inflammatory drug (NSAID) which preferentially blocks cyclo-oxygenase-2 activity, may be less nephrotoxic than indomethacin. This study tested whether nabumetone has effects different from those of indomethacin on exercise-induced changes in renal function and the renin–aldosterone system. In a randomized fashion, ten subjects were studied after indomethacin (100 mg), nabumetone (1 g) or no medication (control) administered orally at 22.00 hours on the day before each study day, and again at 8.00 hours upon arrival at the laboratory. Renal function was studied at baseline, during graded 20-min exercise sessions at 25%, 50% and 75% of the maximal oxygen uptake rate, and subsequently during two 1-h recovery periods. Heart rate, arterial blood pressure, cardiac output and plasma catecholamines at rest and during exercise were not altered by indomethacin or nabumetone. Indomethacin decreased urinary rates of excretion of 6-oxo-prostaglandin F 1α (6-oxo-PGF 1α ) and thromboxane B 2 in all study periods. Nabumetone decreased 6-oxo-PGF 1α excretion during and after exercise. Excretion rates for PGE 2 did not change. Neither indomethacin nor nabumetone changed baseline values or exercise-induced decreases in renal plasma flow or glomerular filtration rate. Indomethacin, but not nabumetone, decreased sodium excretion, urine flow rate and free water clearance. The renal response to exercise, however, remained unchanged. In contrast with nabumatone, indomethacin decreased the plasma renin concentration. Thus, during exercise, nabumetone may decrease the excretion of 6-oxo-PGF 1α by inhibition of cyclo-oxygenase-1 or by inhibition of specific exercise-induced activation of cyclo-oxygenase-2, or both. None of the drugs changed the renal response to exercise. Inhibition by indomethacin of angiotensin II and thromboxane A 2 synthesis may, during exercise, counterbalance renal vasoconstriction caused by blockade of vasodilatory prostaglandins.

Cyclosporin A (CsA) may exert its cytotoxic effects by altering the activity of different plasma membrane transport systems. Although CsA may act at the gene level, it has been also suggested that it can directly alter transport processes at the plasma membrane. To examine this possibility in a physiological context, we determined Na + /K + -ATPase activity in erythrocytes from two groups of subjects receiving CsA treatment: group I consisted of kidney transplant patients, and group II comprised patients with steroid-resistant idiopathic nephrotic syndrome. Group I patients showed a marked decrease (35%) in the activity of the Na + /K + -ATPase in erythrocytes immediately after surgery, before the initiation of CsA treatment. The activity remained low 2 days after the introduction of CsA, but had recovered to the original (pre-surgery) value 1 month later. Group II patients showed the same pattern of erythrocyte Na + /K + -ATPase activity as those in group I. When the blood CsA levels from all patients were plotted against the corresponding erythrocyte Na + /K + -ATPase transport activity, a significant linear correlation was found. Higher levels of CsA in the blood were correlated significantly with increased Na + /K + -ATPase activities. The blood sodium concentration was also correlated positively with both erythrocyte Na + /K + -ATPase activity and blood CsA concentration. Thus CsA treatment is not associated with inhibition of the Na + /K + -ATPase in erythrocytes.

1. Following the observation that brain natriuretic peptide enhances the urinary excretion rate of endothelin-1, the relationship between natriuretic peptides and urinary endothelin-1 was further investigated. Six healthy volunteers received, on three different occasions, increasing doses of atrial or C-type natriuretic peptide (0, 2 and 4 ;pmol·min -1 ·kg -1 for 1 ;h each), or placebo. 2. Atrial natriuretic peptide caused significant increases in the urinary excretion of cGMP, sodium and endothelin-1, without affecting plasma endothelin-1, renal plasma flow, glomerular filtration rate and urine flow rate. C-type natriuretic peptide did not modify any of these parameters. During atrial natriuretic peptide infusion, urinary endothelin-1 directly correlated with plasma atrial natriuretic peptide, urinary cGMP and sodium excretion. 3. These results indicate that enhancement of the urinary excretion of endothelin-1 by natriuretic peptides is dose-dependent and somewhat related to their ability to bind to natriuretic peptide receptors A, activate guanylate cyclase and induce a natriuretic response.

1. Renal specific targeting of the non-steroidal anti-inflammatory drug naproxen was obtained by coupling to the low-molecular-mass protein lysozyme. A previous study showed that conjugation to lysozyme resulted in a 70-fold increase of naproxen accumulation in the kidney with a subsequent renal release of the active metabolite naproxen–lysine. 2. In the present study we questioned whether naproxen–lysozyme is active in the rat kidney, inhibiting the urinary excretion of prostaglandin E 2 and renal sodium and water excretion in salt-restricted baseline conditions as well as during frusemide treatment. 3. A high dose of free naproxen (10 ;mg·day -1 ·kg -1 ) did not affect prostaglandin E 2 excretion in baseline conditions (naproxen, 11±1 ;ng/8 ;h; vehicle, 13±4 ;ng/8 ;h), whereas sodium and water excretion were, respectively, 3.0 and 1.6 times lower in the naproxen group ( P < 0.05). Naproxen completely prevented the frusemide-induced increase (3-fold) in prostaglandin E 2 excretion (naproxen 6.6±1.1 ;ng/8 ;h, vehicle 40±12 ;ng/8 ;h, P < 0.005). Frusemide-stimulated natriuresis and diuresis were, respectively, 1.6 ( P < 0.05) and 1.8 times ( P < 0.005) lower in the naproxen group. 4. A dose of 2 ;mg·day -1 ·kg -1 lysozyme-conjugated naproxen did not affect prostaglandin E 2 excretion in baseline conditions (conjugate, 18±2 ;ng/8 ;h; vehicle, 24±5 ;ng/8 ;h). The conjugate also had no effect on sodium and water excretion. However, the naproxen conjugate completely prevented the frusemide-induced increase (2-fold) in prostaglandin E 2 excretion (conjugate, 16±3 ;ng/8 ;h; vehicle, 48±13 ;ng/8 ;h, P < 0.05). Surprisingly, frusemide-induced natriuresis and diuresis were not affected by the conjugate. 5. In conclusion, a renal specific delivery of the non-steroidal anti-inflammatory drug naproxen using lysozyme results in an inhibitory effect on renal prostaglandin E 2 synthesis but does not affect the excretion of sodium and water, in contrast to free naproxen.

1. Arginine can be produced in the kidney from citrulline. An important source of circulating citrulline is the intestinal breakdown of glutamine. Consequently, partial enterectomy leads to decreased plasma citrulline levels. The aim of the present study was to investigate the effect of diminished arterial citrulline levels on renal arginine production and total-body free arginine pools. 2. Renal amino acid metabolism was studied 24 ;h after 75% small bowel resection in rats fasted overnight (16 ;h) ( n = 12; total fast 40 ;h). Sham-operated ( n = 9) and non-operated 16-h and 40-h fasted controls were studied in parallel ( n = 8/ n = 7). During anaesthesia, l -(2,3- 3 H)-arginine and para -aminohippuric acid were infused until steady state. Subsequently, arterial and renal venous blood samples were taken. Concentrations of para -aminohippurate and amino acids and specific activity of arginine and citrulline were measured to calculate renal plasma flow, net renal uptake or release, and unidirectional influx or efflux of arginine and citrulline, as well as whole-body arginine turnover. 3. Arterial citrulline was decreased in enterectomized rats compared with sham-operated rats (23±3 versus 44±6 ; μ M). Net renal citrulline uptake and arginine release were almost stoichiometric (-36±7 and 38±6 ;nmol·min -1 ·100 ;g -1 body weight respectively in sham-operated rats) and were both diminished by 50% in enterectomized versus sham-operated rats. In all groups, net renal arginine production accounted for less than 10% of whole-body rate of arginine appearance (488 ;nmol·min -1 ·100 ;g -1 body weight in the sham group). Despite decreased net renal citrulline consumption and renal arginine production in enterectomized rats, whole-body rate of arginine appearance and arterial arginine did not change significantly. 4. In conclusion, net renal arginine production is reduced 24 ;h after 75% enterectomy in fasted rats. However, this does not have important effects on whole-body arginine production.