Epilepsy is a highly prevalent neurological disease and anti-epileptic drugs (AED) are almost the unique clinical treatment option. A disbalanced brain renin–angiotensin system (RAS) has been proposed in epilepsy and several reports have shown that angiotensin II (Ang II) receptor-1 (ATR1) activation is pro-inflammatory and pro-epileptogenic. In agreement, ATR1 blockage with the repurposed drug losartan has shown benefits in animal models of epilepsy. Processing of Ang II by ACE2 enzyme renders Ang-(1-7), a metabolite that activates the mitochondrial assembly (Mas) receptor (MasR) pathway. MasR activation presents beneficial effects, facilitating vasodilatation, increasing anti-inflammatory and antioxidative responses. In a recent paper published in Clinical Science , Gomes and colleagues ( Clin. Sci. ( Lond. ) (2020) 134 , 2263–2277) performed intracerebroventricular (icv) infusion of Ang-(1-7) in animals subjected to the pilocarpine model of epilepsy, starting after the first spontaneous motor seizure (SMS). They showed that this approach reduced the frequency of SMS, restored animal anxiety, increased exploration, and augmented the hippocampal expression of protective catalase enzyme and antiapoptotic protein B-cell lymphoma 2 (Bcl-2). Interestingly, but surprisingly, Gomes and colleagues showed that MasR expression and mTor activity were reduced in the hippocampus of the epileptic Ang-(1-7) treated animals. These results show that Ang-(1-7) administration could represent a new avenue for developing strategies for the management of epilepsy in clinical settings. However, future work is necessary to evaluate the levels of RAS metabolites and the activity of key enzymes in these experimental interventions to completely understand the therapeutic potential of the brain RAS manipulation in epilepsy.

The key link between renin–angiotensin system (RAS) and COVID-19 is ACE2 (angiotensin-converting enzyme 2), which acts as a double-edged sword, because ACE2 increases the tissue anti-inflammatory response but it is also the entry receptor for the virus. There is an important controversy on several drugs that regulate RAS activity and possibly ACE2, and are widely used, particularly by patients most vulnerable to severe COVID-19. In the lung of healthy rats, we observed that candesartan (an angiotensin type-1, AT1, receptor blocker; ARB) and captopril (an ACE inhibitor; ACEI) up-regulated expression of tissue ACE2 and RAS anti-inflammatory axis receptors (AT2 and Mas receptors). This effect was particularly pronounced in rats with metabolic syndrome (obesity, increased blood pressure and hyperglycemia) and aged rats. Treatment of cultures of human type-II pneumocytes with candesartan or captopril induced up-regulation of ACE2 expression in cells. Treatment with viral spike protein induced a decrease in full-length (i.e. transmembrane) ACE2, an increase in levels of a short intracellular ACE2 polypeptide and an increase in ADAM17 activity in cells, together with an increase in levels of soluble ACE2 and major proinflammatory cytokines in the culture medium. Spike protein-induced changes and levels of spike protein internalization in cells were inhibited by pretreatment with the above-mentioned drugs. The results suggest that these drugs increase ACE2 levels and promote the anti-inflammatory RAS axis in the lung. Furthermore, possible up-regulation of viral entry by the drug-induced increase in expression of transmembrane ACE2 is counteracted by additional mechanisms, particularly by drug-induced inhibition of ADAM17 activity.

Angiotensin converting enzyme 2 (ACE2) is the major enzyme responsible for conversion of Ang II into Ang-(1-7). It also acts as the receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2, which causes Co rona vi rus D isease (COVID)-19. In recognition of the importance of ACE2 and to celebrate 20 years since its discovery, the journal will publish a focused issue on the basic science and (patho)physiological role of this multifunctional protein.

Rho-kinase has relevant functions in blood pressure modulation and cardiovascular remodeling. Rho-kinase activity is determined in circulating leukocytes measuring phosphorylation of its target myosin phosphatase target subunit 1 (MYPT1), but its relationship with Rho-kinase activity in the myocardium and in vasculature in hypertension has not been evaluated. The aim was to determine the degree of association between Rho-kinase cascade activation in circulating leukocytes with cardiac and aortic Rho-kinase pathway activation in a model of hypertension and to analyze it with a cause–effect perspective. Hypertensive deoxycorticosterone (DOCA)-salt rats received the Rho-kinase antagonist fasudil (DOCA-Fas, 100 mg/kg/day, 3 weeks). Results were compared with an untreated DOCA-salt and a sham group. Rho-kinase inhibition reduced significantly blood pressure, cardiac hypertrophy, myocardial collagen and macrophage infiltration, but not aortic wall hypertrophy. Fasudil decreased significantly Rho-kinase activity in peripheral blood mononucleated cells (PBMC), myocardium and aortic wall to similar levels as in the sham group. A significant correlation was found between PBMC Rho-kinase activity and cardiac remodeling, specifically with hypertrophy ( r = 0.51, P ≤0.01), myocardial collagen ( r = 0.40, P ≤0.05) and ED1 immunostaining ( r = 0.48, P ≤0.01). In the untreated hypertensive group, increased levels ( P <0.05) of the proinflammatory molecules p65 NF-κB, vascular cell adhesion molecule 1 and interleukin-6 antibody in the myocardium, aortic wall and PBMC were observed and were reduced with fasudil ( P <0.05). In conclusion, in this hypertension model, Rho-kinase and its pathway activation determined in circulating leukocytes reflect the activation of this pathway in the myocardium and in the aortic wall and are significantly related to myocardial remodeling (hypertrophy, fibrosis and inflammation).

Stroke is a devastating disease that afflicts millions of people each year worldwide. Ischemic stroke, which accounts for ~88% of cases, occurs when blood supply to the brain is decreased, often because of thromboembolism or atherosclerotic occlusion. This deprives the brain of oxygen and nutrients, causing immediate, irreversible necrosis within the core of the ischemic area, but more delayed and potentially reversible neuronal damage in the surrounding brain tissue, the penumbra. The only currently approved therapies for ischemic stroke, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) and the endovascular clot retrieval/destruction processes, are aimed at restoring blood flow to the infarcted area, but are only available for a minority of patients and are not able in most cases to completely restore neurological deficits. Consequently, there remains a need for agents that will protect neurones against death following ischemic stroke. Here, we evaluate angiotensin II (Ang II) type 2 (AT 2 ) receptor agonists as a possible therapeutic target for this disease. We first provide an overview of stroke epidemiology, pathophysiology, and currently approved therapies. We next review the large amount of preclinical evidence, accumulated over the past decade and a half, which indicates that AT 2 receptor agonists exert significant neuroprotective effects in various animal models, and discuss the potential mechanisms involved. Finally, after discussing the challenges of delivering blood–brain barrier (BBB) impermeable AT 2 receptor agonists to the infarcted areas of the brain, we summarize the evidence for and against the development of these agents as a promising therapeutic strategy for ischemic stroke.

The existence of a so-called brain renin-angiotensin system (RAS) is controversial. Given the presence of the blood–brain barrier, angiotensin generation in the brain, if occurring, should depend on local synthesis of renin and angiotensinogen. Yet, although initially brain-selective expression of intracellular renin was reported, data in intracellular renin knockout animals argue against a role for this renin in angiotensin generation. Moreover, renin levels in brain tissue at most represented renin in trapped blood. Additionally, in neurogenic hypertension brain prorenin up-regulation has been claimed, which would generate angiotensin following its binding to the (pro)renin receptor. However, recent studies reported no evidence for prorenin expression in the brain, nor for its selective up-regulation in neurogenic hypertension, and the (pro)renin receptor rather displays RAS-unrelated functions. Finally, although angiotensinogen mRNA is detectable in the brain, brain angiotensinogen protein levels are low, and even these low levels might be an overestimation due to assay artefacts. Taken together, independent angiotensin generation in the brain is unlikely. Indeed, brain angiotensin levels are extremely low, with angiotensin (Ang) I levels corresponding to the small amounts of Ang I in trapped blood plasma, and Ang II levels at most representing Ang II bound to (vascular) brain Ang II type 1 receptors. This review concludes with a unifying concept proposing the blood origin of angiotensin in the brain, possibly resulting in increased levels following blood–brain barrier disruption (e.g. due to hypertension), and suggesting that interfering with either intracellular renin or the (pro)renin receptor has consequences in an RAS-independent manner.

Significant neuroprotective effects of angiotensin II type 2 (AT 2 ) receptor (AT 2 receptor) agonists in ischemic stroke have been previously demonstrated in multiple studies. However, the routes of agonist application used in these pre-clinical studies, direct intracerebroventricular (ICV) and systemic administration, are unsuitable for translation into humans; in the latter case because AT 2 receptor agonists are blood–brain barrier (BBB) impermeable. To circumvent this problem, in the current study we utilized the nose-to-brain (N2B) route of administration to bypass the BBB and deliver the selective AT 2 receptor agonist Compound 21 (C21) to naïve rats or rats that had undergone endothelin 1 (ET-1)-induced ischemic stroke. The results obtained from the present study indicated that C21 applied N2B entered the cerebral cortex and striatum within 30 min in amounts that are therapeutically relevant (8.4–9 nM), regardless of whether BBB was intact or disintegrated. C21 was first applied N2B at 1.5 h after stroke indeed provided neuroprotection, as evidenced by a highly significant, 57% reduction in cerebral infarct size and significant improvements in Bederson and Garcia neurological scores. N2B-administered C21 did not affect blood pressure or heart rate. Thus, these data provide proof-of-principle for the idea that N2B application of an AT 2 receptor agonist can exert neuroprotective actions when administered following ischemic stroke. Since N2B delivery of other agents has been shown to be effective in certain human central nervous system diseases, the N2B application of AT 2 receptor agonists may become a viable mode of delivering these neuroprotective agents for human ischemic stroke patients.

The renin–angiotensin system (RAS) and obesity have been implicated in vascular outward remodeling, including aneurysms, but the precise mechanisms are not yet understood. We investigated the effect of the angiotensin receptor type 1 (AT1-receptor) antagonist telmisartan on aortic outward remodeling in a diet-induced obesity model in mice. C57/Black6J mice were fed either a low-fat diet (LFD) or a high-fat diet (HFD) for 14 weeks. One group of HFD mice was additionally exposed to telmisartan (3 mg/kg per day) for the last 4 weeks. HFD led to aortic outward remodeling, characterized by increased proteolysis, along with structural changes, such as fragmentation of elastic fibers and decreased elastin content. Vascular damage was associated with up-regulation of matrix metalloproteinase (MMP)-2 (MMP-2), MMP-3, MMP-12, cathepsin D, and cathepsin B. HFD aortae exhibited an enhanced inflammatory status, characterized by tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β) colocalized with adipocytes in the adventitia. HFD resulted in a significant increase in aortic dimensions, evident by ultrasound measurements. Telmisartan abolished aortic dilatation and preserved elastin content. HFD induced enhanced expression of aortic MMP-2, MMP-9, and TNF-α was abrogated by telmisartan. Adventitial proteolytic and inflammatory factors were also examined in samples from human abdominal aneurysms. The expression of TNF-α, IL-1β, and MMP-9 was higher in the adventitial fat of diseased vessels compared with healthy tissues. Finally, adipocytes treated with TNF-α showed enhanced MMP-2, MMP-3, and cathepsin D, which was prevented by telmisartan. Taken together, HFD in mice induced aortic dilatation with up-regulation of matrix degrading and inflammatory pathways similar to those seen in human aortic aneurysmatic tissue. The HFD-induced vascular pathology was reduced by AT1-receptor antagonist telmisartan.

Hypertension affects one-third of adults in the Western world and is the most common independent risk factor for cardiovascular disease, and the leading cause of premature death globally. Despite available therapeutic options, approximately half of the hypertensive population taking medication does not achieve adequate blood pressure (BP) control leaving them at increased risk of chronic kidney disease, renal failure, stroke, congestive heart failure, myocardial infarction, aneurysm and peripheral artery disease. New therapeutic options need to be identified for the treatment of hypertension in order to increase the percentage of individuals with controlled BP. There is a growing basic science literature regarding the role of T-cells in the pathogenesis of hypertension and BP control; however, the majority of this literature has been performed exclusively in males despite the fact that both men and women develop hypertension. This is especially problematic since hypertension is well recognized as having distinct sex differences in the prevalence, absolute BP values and molecular mechanisms contributing to the pathophysiology of the disease. The purpose of this article is to review the available literature regarding sex differences in T-cells in hypertension followed by highlighting the potential pathways that may result in sex-specific effects on T-cell activation and differentiation.

The RAS (renin–angiotensin system) is integral to cardiovascular physiology; however, dysregulation of this system largely contributes to the pathophysiology of CVD (cardiovascular disease). It is well established that AngII (angiotensin II), the main effector of the RAS, engages the AT 1 R (angiotensin type 1 receptor) and promotes cell growth, proliferation, migration and oxidative stress, all processes which contribute to remodelling of the heart and vasculature, ultimately leading to the development and progression of various CVDs, including heart failure and atherosclerosis. The counter-regulatory axis of the RAS, which is centred on the actions of ACE2 (angiotensin-converting enzyme 2) and the resultant production of Ang-(1–7) [angiotensin-(1–7)] from AngII, antagonizes the actions of AngII via the receptor Mas, thereby providing a protective role in CVD. More recently, another ACE2 metabolite, Ang-(1–9) [angiotensin-(1–9)], has been reported to be a biologically active peptide within the counter-regulatory axis of the RAS. The present review will discuss the role of the counter-regulatory RAS peptides Ang-(1–7) and Ang-(1–9) in the cardiovascular system, with a focus on their effects in remodelling of the heart and vasculature.

The goal of the present review is to examine the evidence for beneficial actions of manipulation of the RAS (renin–angiotensin system) in stroke, with particular focus on Ang-(1–7) [angiotensin-(1–7)] and its receptor Mas. The RAS appears to be highly involved in the multifactorial pathophysiology of stroke. Blocking the effects of AngII (angiotensin II) at AT 1 R (AngII type 1 receptor), through the use of commonly prescribed ACE (angiotensin-converting enzyme) inhibitors or AT 1 R blockers, has been shown to have therapeutic effects in both ischaemic and haemorrhagic stroke. In contrast with the deleterious actions of over activation of AT 1 R by AngII, stimulation of AT 2 Rs (AngII type 2 receptors) in the brain has been demonstrated to elicit beneficial effects in stroke. Likewise, the ACE2/Ang-(1–7)/Mas axis of the RAS has been shown to have therapeutic effects in stroke when activated, countering the effects of the ACE/AngII/AT 1 R axis. Studies have demonstrated that activating this axis in the brain elicits beneficial cerebral effects in rat models of ischaemic stroke, and we have also demonstrated the cerebroprotective potential of this axis in haemorrhagic stroke using stroke-prone spontaneously hypertensive rats and collagenase-induced striatal haemorrhage. The mechanism of cerebroprotection elicited by ACE2/Ang-(1–7)/Mas activation includes anti-inflammatory effects within the brain parenchyma. The major hurdle to overcome in translating these results to humans is devising strategies to activate the ACE2/Ang-(1–7)/Mas cerebroprotective axis using post-stroke treatments that can be administered non-invasively.

Aortic aneurysms are relatively common maladies that may lead to the devastating consequence of aortic rupture. AAAs (abdominal aortic aneurysms) and TAAs (thoracic aortic aneurysms) are two common forms of aneurysmal diseases in humans that appear to have distinct pathologies and mechanisms. Despite this divergence, there are numerous and consistent demonstrations that overactivation of the RAS (renin–angiotensin system) promotes both AAAs and TAAs in animal models. For example, in mice, both AAAs and TAAs are formed during infusion of AngII (angiotensin II), the major bioactive peptide in the RAS. There are many proposed mechanisms by which the RAS initiates and perpetuates aortic aneurysms, including effects of AngII on a diverse array of cell types and mediators. These experimental findings are complemented in humans by genetic association studies and retrospective analyses of clinical data that generally support a role of the RAS in both AAAs and TAAs. Given the lack of a validated pharmacological therapy for any form of aortic aneurysm, there is a pressing need to determine whether the consistent findings on the role of the RAS in animal models are translatable to humans afflicted with these diseases. The present review compiles the recent literature that has shown the RAS as a critical component in the pathogenesis of aortic aneurysms.

Local and systemic AngII (angiotensin II) levels are regulated by ACE2 (angiotensin-converting enzyme 2), which is reduced in diabetic tissues. In the present study, we examine the effect of ACE2 deficiency on the early cardiac and vascular changes associated with experimental diabetes. Streptozotocin diabetes was induced in male C57BL6 mice and Ace2 -KO (knockout) mice, and markers of RAS (renin–angiotensin system) activity, cardiac function and injury were assessed after 10 weeks. In a second protocol, diabetes was induced in male ApoE (apolipoprotein E)-KO mice and ApoE / Ace2 -double-KO mice, and plaque accumulation and markers of atherogenesis assessed after 20 weeks. The induction of diabetes in wild-type mice led to reduced ACE2 expression and activity in the heart, elevated circulating AngII levels and reduced cardiac Ang-(1–7) [angiotensin-(1–7)] levels. This was associated structurally with thinning of the LV (left ventricular) wall and mild ventricular dilatation, and histologically with increased cardiomyocyte apoptosis on TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) staining and compensatory hypertrophy denoted by an increased cardiomyocyte cross-sectional area. By contrast Ace2 -KO mice failed to increase circulating AngII concentration, experienced a paradoxical fall in cardiac AngII levels and no change in Ang-(1–7) following the onset of diabetes. At the same time the major phenotypic differences between Ace2 -deficient and Ace2 -replete mice with respect to BP (blood pressure) and cardiac hypertrophy were eliminated following the induction of diabetes. Consistent with findings in the heart, the accelerated atherosclerosis that was observed in diabetic ApoE -KO mice was not seen in diabetic ApoE / Ace2 -KO mice, which experienced no further increase in plaque accumulation or expression in key adhesion molecules beyond that seen in ApoE / Ace2 -KO mice. These results point to the potential role of ACE2 deficiency in regulating the tissue and circulating levels of AngII and their sequelae in the context of diabetes, as well as the preservation or augmentation of ACE2 expression or activity as a potential therapeutic target for the prevention of CVD (cardiovascular disease) in diabetes.

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.

Modulation of the RAS (renin–angiotensin system), in particular of the function of the hormones AngII (angiotensin II) and Ang-(1–7) [angiotensin-(1–7)], is an important target for pharmacotherapy in the cardiovascular system. In the classical view, such modulation affects cardiovascular cells to decrease hypertrophy, fibrosis and endothelial dysfunction, and improves diuresis. In this view, excessive stimulation of AT 1 receptors (AngII type 1 receptors) fulfils a detrimental role, as it promotes cardiovascular pathogenesis, and this is opposed by stimulation of the AT 2 receptor (angiotensin II type 2 receptor) and the Ang-(1–7) receptor encoded by the Mas proto-oncogene. In recent years, this view has been broadened with the observation that the RAS regulates bone marrow stromal cells and stem cells, thus involving haematopoiesis and tissue regeneration by progenitor cells. This change of paradigm has enlarged the field of perspectives for therapeutic application of existing as well as newly developed medicines that alter angiotensin signalling, which now stretches beyond cardiovascular therapy. In the present article, we review the role of AngII and Ang-(1–7) and their respective receptors in haematopoietic and mesenchymal stem cells, and discuss possible pharmacotherapeutical implications.

AngII (angiotensin II) induces atherosclerosis and AAAs (abdominal aortic aneurysms) through multiple proposed mechanisms, including chemotaxis. Therefore, we determined the effects of whole-body deficiency of the chemokine receptor CCR2 (CC chemokine receptor 2) on these diseases. To meet this objective, apoE (apolipoprotein E) −/− mice that were either CCR2 +/+ or CCR2 −/− , were infused with either saline or AngII (1000 ng·kg −1 of body weight·min −1 ) for 28 days via mini-osmotic pumps. Deficiency of CCR2 markedly attenuated both atherosclerosis and AAAs, unrelated to systolic blood pressure or plasma cholesterol concentrations. During the course of the present study, we also observed that AngII infusion led to large dilatations that were restricted to the ascending aortic region of apoE −/− mice. The aortic media in most of the dilated area was thickened. In regions of medial thickening, distinct elastin layers were discernable. There was an expansion of the distance between elastin layers in a gradient from the intimal to the adventitial aspect of the media. This pathology differed in a circumscribed area of the anterior region of ascending aortas in which elastin breaks were focal and almost transmural. All regions of the ascending aorta of AngII-infused mice had diffuse medial macrophage accumulation. Deficiency of CCR2 greatly attenuated the AngII-induced lumen dilatation in the ascending aorta. This new model of ascending aortic aneurysms has pathology that differs markedly from AngII-induced atherosclerosis or AAAs, but all vascular pathologies were attenuated by CCR2 deficiency.

Intervention in the RAAS (renin–angiotensin–aldosterone system) is one of the leading pharmacotherapeutic strategies, among others, used for the treatment of cardiovascular disease to improve the prognosis after myocardial infarction and to reduce hypertension. Recently, regenerative progenitor cell therapy has emerged as a possible alternative for pharmacotherapy in patients after myocardial infarction or ischaemic events elsewhere, e.g. in the limbs. Angiogenic cell therapy to restore the vascular bed in ischaemic tissues is currently being tested in a multitude of clinical studies. This has prompted researchers to investigate the effect of modulation of the RAAS on progenitor cells. Furthermore, the relationship between hypertension and endothelial progenitor cell function is being studied. Pharmacotherapy by means of angiotensin II type 1 receptor antagonists or angiotensin-converting enzyme inhibitors has varying effects on progenitor cell levels and function. These controversial effects may be explained by involvement of multiple mediators, e.g. angiotensin II and angiotensin-(1–7), that have differential effects on mesenchymal stem cells, haematopoietic progenitor cells and endothelial progenitor cells. Importantly, angiotensin II can either stimulate endothelial progenitor cells by improvement of vascular endothelial growth factor signalling, or invoke excessive production of reactive oxygen species causing premature senescence of these cells. On the other hand, angiotensin-(1–7) stimulates haematopoietic cells and possibly also endothelial progenitor cells. Furthermore, aldosterone, bradykinin and Ac-SDKP ( N -acetyl-Ser-Asp-Lys-Pro) may also affect progenitor cell populations. Alternatively, the variability in effects of angiotensin II type 1 receptor and angiotensin-converting enzyme inhibition on cardiovascular progenitor cells might reflect differences between the various models or diseases with respect to circulating and local tissue RAAS activation. In the present review we discuss what is currently known with respect to the role of the RAAS in the regulation of cardiovascular progenitor cells.

In the present issue of Clinical Science , Brown and co-workers report preliminary results of Ang I (angiotensin I) immunization in humans. They demonstrate the presence of antibodies in human plasma and report that the procedure is well tolerated, but the blood pressure does not fall. The first attempts to actively immunize against components of the renin–angiotensin system were performed by Goldblatt in the 1950s. In our experience, active immunization against renin was associated with a complete inhibition of endogeneous plasma renin activity and a decrease in blood pressure, followed by the progressive development of a juxtaglomerular autoimmune nephritis. In contrast neither blood pressure nor aldosterone secretion were significantly modified by Ang I immunization. Moreover, Ang I-immunized animals continued to respond to the pharmacological inhibition of renin–angiotensin system. These data provide evidence of the inability of antibodies to target Ang I within tissues.

Immunization against components of the renin–angiotensin system offers a potential alternative to daily medication in some patients with hypertension or heart failure. Our primary objective was to determine whether a sustained antibody titre to Ang I (angiotensin I) can be achieved in hypertensive patients. The secondary objective was to determine whether the antibodies block the renin system. Patients ( n =27) with essential hypertension responsive to an ACEi (angiotensin-converting enzyme inhibitor) or ARB (angiotensin blocker) were randomly assigned to receive three or four injections of the Ang I vaccine PMD3117 or aluminium hydroxide (Alhydrogel™) over a 6 week period. Antibody titre was measured prior to each injection and every 30 days until disappearance. Indices of renin blockade were changes in renin and aldosterone (blood and urine) and a within-patient comparison of the pre- and post-vaccination rise in 24 h ambulatory blood pressure after 2 weeks of withdrawal of ACEi or ARB. The anti-(Ang I) antibody titre rose from the second injection in both regimes and peaked on day 64. Median half-life was 85 (95% CI, 44 and 153) days (where CI is confidence interval). Vaccination did not influence blood pressure, but significantly blunted the fall in plasma renin following withdrawal of ACEi or ARB. At 42 days after the first injection, aldosterone excretion was decreased by PMD3117 to 6 (95% CI, 1 and 31)% of values in patients receiving Alhydrogel™ ( P =0.012). In patients with essential hypertension, PMD3117 generated a prolonged antibody response to Ang I. Biochemical measurements show evidence of blockade of the renin system, but higher titres will be required to achieve a decrease in blood pressure.

Continuous intra-arterial administration of a selective endothelin-converting enzyme (ECE) inhibitor CGS 35066 at a dose of 30mg/kg decreased the mean arterial blood pressure (MABP) in conscious unrestrained normotensive rats and spontaneously hypertensive rats (SHRs). At that dose, the magnitude of the antihypertensive effects was greater in SHRs than in normotensive rats. Additional administration of an angiotensin-converting enzyme (ACE) inhibitor benazapril (lotensin) further reduced MABP in normotensive rats and completely blocked hypertension in SHRs. However, when the selective ECE inhibitor was subsequently removed, blood pressure was less inhibited in normotenive rats whereas it remained strongly inhibited in SHRs by the ACE inhibitor alone. These results imply that simultaneous treatment with benazepril and CGS 35066 gave additive antihypertensive effects in normotensive rats but not in SHRs, when both compounds were administered at a dose of 30mg/kg. Our results suggest that: (i) the endothelin (ET) system together with the renin–angiotensin system contribute to the maintenance of blood pressure in normal healthy rats; (ii) while an ECE inhibitor acts as an antihypertensive agent on its own, the sole efficacy of ACE inhibitor at that dose is sufficient to block MABP without the participation of the ET system in SHR.

The present study was designed to prospectively test the hypothesis that gene polymorphisms of the renin-angiotensin system are associated with recurrent restenosis after repeated percutaneous transluminal coronary angioplasty. Five hundred and eleven patients after first successful angioplasty were characterized with respect to the angiotensinogen M235T, angiotensin-converting enzyme insertion/deletion and angiotensin II type 1 receptor A1166C gene polymorphisms. In 164 of these patients repeated angioplasty on a restenotic lesion was performed. After repeated angioplasty, 46 patients had recurrent restenosis as defined by a greater than 50% progression of residual stenosis. In the recurrent restenosis group there was a statistically significant higher percentage of patients receiving cholesterol-lowering drugs compared with the group of patients without recurrent restenosis. The two groups of patients did not differ with respect to procedural and angiographic parameters. There were significantly more carriers of the angiotensinogen 235T allele in the recurrent restenosis group than in the control group without recurrent restenosis. No differences between the two groups were found with respect to the other gene polymorphisms investigated. According to the results of a multifactorial analysis of variance, only the 235T allele of the angiotensinogen gene and not cholesterol drug therapy independently affected the increase of stenosis at follow-up angiography. In conclusion, the angiotensinogen 235T allele may be an independent predictor for recurrent restenosis after repeated angioplasty.

The objective of the present study was to determine the autonomic effects of angiotensin II (AT 1 ) receptor blocker therapy in heart failure. In a randomized double-blind cross-over study, we compared the effects of candesartan and placebo on baroreflex sensitivity and on heart rate variability at rest, during stress and during 24h monitoring. Acute effects were assessed 4h after oral candesartan (8mg) and chronic effects after 4 weeks of treatment (dose titrated to 16mg daily). The study group comprised 21 patients with heart failure [mean (S.E.M.) ejection fraction 33% (1%)], in the absence of angiotensin-converting enzyme (ACE) inhibitor therapy. We found that acute candesartan was not different from placebo in its effects on blood pressure or mean RR interval. Chronic candesartan significantly reduced blood pressure [placebo, 137 (3)/82 (3)mmHg; candesartan, 121 (4)/75 (2)mmHg; P <0.001; values are mean (S.E.M.)], but had no effect on mean RR interval [placebo, 857 (25)ms; candesartan, 857 (21)ms]. Compared with placebo there were no significant effects of acute or chronic candesartan on heart rate variability in the time domain and no consistent effects in the frequency domain. Baroreflex sensitivity assessed by the phenylephrine bolus method was significantly increased after chronic candesartan [placebo, 3.5 (0.5)ms/mmHg; candesartan, 4.8 (0.7)ms/mmHg; P <0.05], although there were no changes in cross-spectral baroreflex sensitivity. Thus, in contrast with previous results with ACE inhibitors, angiotensin II receptor blockade in heart failure did not increase heart rate variability, and there was no consistent effect on baroreflex sensitivity.

Angiotensin II (Ang II) is a multi-functional hormone that plays a major role in regulating blood pressure and cardiovascular homoeostasis. The actions of Ang II are mediated by at least two receptor subtypes, designated AT 1 and AT 2 . In addition, other angiotensin receptors have been identified which may recognize other angiotensin peptide fragments; however, until now only the AT 1 and AT 2 receptor have been cloned in animals or humans. Most of the well-described actions of Ang II, such as vasoconstriction, facilitation of sympathetic transmission, stimulation of aldosterone release and promotion of cellular growth are all mediated by the AT 1 receptor. Much less is known about the function of the AT 2 receptor, but recent studies suggest that it may play a role in mediating anti-proliferation, cellular differentiation, apoptosis and vasodilatation. In this review, we discuss recent advances in our understanding of Ang II receptors, in particular, their distribution, signalling and function.

We examined the ability of the new non-peptide angiotensin II receptor antagonist irbesartan to inhibit AT 1 receptors in vivo in the rat kidney following oral administration, compared with the prototype drug losartan. Male Sprague–Dawley rats (250–300 g) were gavaged with either irbesartan or losartan at doses of 1, 3, 10, 30 or 100 mg/kg, or with corresponding vehicle. Rats were killed at 0, 1, 2, 8, or 24 h after drug administration, trunk blood was collected and the kidneys were removed. The effects of irbesartan and losartan on angiotensin II receptor binding were determined by quantitative in vitro autoradiography using the specific radioligand 125 I-[Sar 1 ,Ile 8 ]angiotensin II. High levels of angiotensin II receptor binding in the rat kidney were demonstrated in the glomeruli and inner stripe of the outer medulla, which was attributed to AT 1 receptors. At 1 h after dosing, irbesartan (1–100 mg/kg) and losartan (1–30 mg/kg) significantly inhibited AT 1 receptor binding in all anatomical areas of the kidney, in a dose-dependent manner, with a maximal effect at 100 mg/kg and 30 mg/kg respectively. For a 10 mg/kg dose, inhibition of AT 1 receptor binding was maximal around 1–2 h after oral administration of losartan, whereas maximal binding occurred between 2 and 8 h for irbesartan; both drugs produced persistent tissue blockade at 24h. In radioligand binding studies, irbesartan, losartan and EXP3174 (1×10 -10 to 1×10 -5 M) displaced 125 I-[Sar 1 ,Ile 8 ]angiotensin II binding from renal AT 1 receptors in a concentration-dependent manner, with a rank order of potency of irbesartan > EXP3174 > losartan. The concentration required to displace 50% of radioligand binding (IC 50 ) by irbesartan, EXP3174 and losartan was 1.00±0.2 nM, 3.5±0.4 nM and 8.9±1.1 nM respectively. In conclusion, the findings of the present study suggest that irbesartan and losartan produce effective and sustained inhibition of AT 1 receptors in vivo in the kidney following oral administration. However, irbesartan appears less potent, with respect to dosage, than losartan in vivo , despite having a higher affinity for AT 1 receptors in vitro . The reason for this apparent discrepancy is unclear, but it may reflect the slower onset of action of irbesartan and its rate of tissue accessibility. Inhibition of angiotensin II receptors in target tissues such as the kidney may represent an important action of AT 1 receptor antagonists, which may contribute to the beneficial effects of these agents in the clinical setting.

The therapeutic benefit of percutaneous transluminal coronary angioplasty (PTCA) is limited by restenosis in 30–40% of patients. The underlying mechanisms are currently not well understood. Besides clinical and angiographic variables, genetic factors may be involved. In the present study, we investigated the associations between the angiotensinogen T174M and M235T, the angiotensin I-converting enzyme (ACE) I/D and the angiotensin II type 1 receptor A1166C gene polymorphisms and restenosis in 511 patients who had undergone successful PTCA (without stenting) and follow-up angiography. Clinical and angiographic variables were also considered as possible predictors of restenosis. Stenosis severity was estimated by visual inspection of the angiograms. Altogether, 160 patients had restenosis, as defined by a greater than 50% reduction in the diameter of the dilated segment at follow-up angiography compared with the findings immediately following angioplasty. There were significantly more carriers of the angiotensinogen 235T allele and more patients with the ACE DD genotype in the restenosis group than in the no restenosis group, but only the angiotensinogen 235T allele (and not the ACE DD genotype) remained significantly associated with restenosis following multifactorial analyses. No differences between the two groups were found with respect to the other gene polymorphisms. Patients who subsequently developed restenosis had a higher degree of stenosis and more severe lesions before PTCA, as well as less residual stenosis immediately after PTCA. We conclude that the angiotensinogen M235T gene polymorphism may be an independent predictor of restenosis after PTCA.

1. We have reported that the renin-angiotensin system is activated in acute asthma, and also by high-dose nebulized β 2 -agonists. The contribution of other possible stimuli such as hypoxia is unknown. The present study examined the effect of hypoxia alone and also combined with β 2 -agonists on the activity of the renin-angiotensin system. 2. In a double-blind crossover study, eight healthy subjects were randomized to inhale a hypoxic (FiO 2 = 12%) or normoxic mixture for a period of 30 min, with either nebulized salbutamol (5 mg) or placebo administered into the circuit after 10 min. Plasma renin, angiotensin II and serum angiotensin-converting enzyme were measured at baseline and at intervals up to 2 h. Pulse rate and oxygen saturation were monitored continuously throughout the study. 3. After hypoxia alone, there was no change in the levels of plasma renin or angiotensin II. When salbutamol was added to the hypoxic mixture, there was a significant rise in plasma renin and angiotensin II [mean (SEM) maximal increase in angiotensin II of 5.6 (2.9)pg/ml and renin of 15.5 (6.3) μ-units/ml at 60 min, P < 0.05 compared with normoxia]. When salbutamol was administered in the normoxic mixture, plasma renin and angiotensin II also increased but this effect was similar to the effect of salbutamol in the hypoxic mixture. Serum angiotensin-converting enzyme levels were unaffected by hypoxia or salbutamol. 4. We conclude from these results that there is activation of the renin—angiotensin system in healthy subjects by salbutamol, but not hypoxia. In addition, the effect of salbutamol on the renin—angiotensin system is not influenced by the presence of hypoxia. As similar levels of hypoxia occur in acute exacerbations of asthma, it seems unlikely that hypoxia is contributing to activation of the renin—angiotensin system in acute severe asthma.

1. Decreased pressor sensitivity to angiotensin II occurs in cirrhosis, but the mechanism remains unclear. 2. Angiotensin II dose-response studies were performed in conscious, chronically instrumented cirrhotic and control rats, and angiotensin II concentration-response studies were performed in isolated blood vessels obtained from similar groups of animals. 3. Cirrhotic rats demonstrated a significantly decreased pressor response to angiotensin II (5-80 ng/kg intravenously). However, angiotensin II-generated tension in thoracic aortic rings isolated from cirrhotic rats and studied in vitro was not impaired. These findings are consistent with the concept that circulating vasodilator substances in cirrhosis rather than an abnormality intrinsic to vascular smooth muscle cells are responsible for the decreased pressor sensitivity to angiotensin II in vivo. 4. Pretreatment with the cyclo-oxygenase inhibitor indomethacin (3 mg/kg intravenously) restored pressor sensitivity to angiotensin II to normal, suggesting that cyclo-oxygenase products, possibily vasodilator prostaglandins, may be involved in mediating pressor resistance to this hormone in vivo.

1. Cardiovascular reactivity, blood vessel morphology, blood pressure and the activity of the renin—angiotensin system were determined in the 3-week-old spontaneously hypertensive (SHR), Wistar—Kyoto (WKY) and outbred Wistar (WIS) rat. 2. In an isolated perfused mesenteric artery preparation the SHR had a significantly increased maximum response to KCl and noradrenaline ( P < 0.02) compared with the WKY. Using a myograph, vascular structure was measured over a range of resistance arteries and showed a significant correlation between lumen diameter and both media cross-sectional area and thickness, with the regression line for the SHR shifted upwards indicating both increased media area and thickness. This was associated with a slight, but significant, narrowing of the lumen ( P < 0.01) and an increased media/lumen ratio (0.049 ±0.01, 0.034 ±0.007, 0.036 ±0.008 for SHR, WKY and WIS, respectively, means ±sd P < 0.001). The SHR had a greater heart/body weight ratio than either the WKY or the WIS ( P < 0.001). 3. Both mesenteric artery and membrane protein content were higher in the SHR, indicating an increase in cell size or number. 4. Plasma renin activity (means ±sd) was lower in the SHR (1.0 ± 0.7 pmol of angiotensin I h −1 ml −1 ) than in the WKY (2.2±1.2 pmol of angiotensin I h −1 ml −1 , P < 0.001) but not different from that in the WIS (1.2±0.8 pmol of angiotensin I h −1 ml −1 ). Mesenteric artery vascular renin concentration was also lower in the SHR ( P = 0.06). Plasma angiotensin II concentration (mean±sd) was similarly lower in the SHR (11.9 ±3.8 fmol/ml) than in the WKY (18.8 ± 6.2 fmol/ml, P < 0.001) but not different from that in the WIS (14.5 ±5.8 fmol/ml). There was no difference in angiotensin II receptor number or affinity between the three rat strains. 5. Quiescent intra-arterial blood pressure was significantly higher in the SHR both 1 and 2 days after cannula insertion. On day 2 the pressure (mean ± sd) in the SHR was 112.7 ± 19.9 mmHg, in the WKY 81.1 ± 14.4 mmHg and in the WIS 75.1 ± 7.8 mmHg ( P < 0.001). 6. These data indicate the presence of marked vascular and cardiac hypertrophy in the SHR at a very early period in its development. Blood pressure is elevated and there is no overactivity of the renin system. We conclude that, at this time, there is no prehypertensive phase nor is there evidence of angiotensin II-mediated pressure-independent mechanism in the hypertrophic development.

1. Active plasma renin concentration but not total renin concentration is reduced in women with pregnancy-induced hypertension compared with normotensive pregnant women. This study was conducted to determine whether women with pregnancy-induced hypertension are able to stimulate release of active renin. 2. Active plasma renin concentration was measured as the generation of angiotensin I at physiological pH in the presence of excess renin substrate, and total renin concentration was determined in the same way after trypsin activation. Inactive plasma renin concentration was calculated as the difference between total renin and active plasma renin concentrations. 3. Resting active plasma renin concentration was significantly greater in third-trimester primigravidae compared with normotensive non-pregnant women and active plasma renin and total renin concentrations rose significantly without a fall in inactive plasma renin concentration in both groups after 2 h ambulation, suggesting increased release of active plasma renin and not conversion of circulating inactive to active renin. These responses were blunted in women taking oral contraceptives. 4. Although the active plasma renin concentration was significantly reduced in third-trimester primigravidae with pregnancy-induced hypertension, total renin concentration was not significantly different compared with normotensive women of similar gestation and in both groups 30 min 60° head-up tilt increased active but not inactive plasma renin concentration. 5. These studies show that in normal pregnancy active plasma renin concentration can be stimulated to a similar extent as in non-pregnant women, despite a higher resting level. This appears to be due to increased secretion of active plasma renin rather than conversion of circulating inactive to active renin. Women with pregnancy-induced hypertension are also still able to stimulate secretion of active renin despite resting concentrations similar to those of non-pregnant women. These data suggest that in pregnancy-induced hypertension basal secretion of active renin is prematurely reset to that in the non-pregnant state but that secretion of active renin responds normally to posture.

1. The fall in renal sodium excretion after dietary sodium restriction is prompt and reproducible. The importance of increased aldosterone secretion during the early phase (within 48 h) of this response is unclear. Using two indirect measures of aldosterone secretion (in urine and saliva), we have tried to relate changes in excretion and concentration of this hormone to renal sodium excretion during the abrupt transition from a normal (approximately 150 mmol/day) or high (260 mmol/day) to a low (5–25 mmol/day) sodium intake in 11 and seven male volunteers, respectively. 2. All subjects showed reduced renal sodium excretion within 36 h of dietary restriction, but the times at which increases in renal aldosterone excretion, saliva aldosterone concentration and plasma renin activity became statistically significant varied widely (8–72 h, 2.5–>62.5 h and 38 h for renal aldosterone secretion, saliva aldosterone concentration and plasma renin activity, respectively). Circadian fluctuations in saliva aldosterone concentration were apparent and increased in amplitude during sodium restriction. 3. Urine flow rate tended to increase on the first day of sodium restriction and this reached statistical significance in the group initially on a high sodium intake (64.0 ± 8.8 to 84.3 ± 11.2 ml/h, P <0.01); although the pattern of urine flow did correlate with plasma arginine vasopressin concentration ( r = −0.49, P <0.01), there was no significant decrease in mean plasma arginine vasopressin concentration [1.15 (0.92–1.44) to 0.90 (0.72–1.12) pmol/l, P = 0.08; geometric mean and 95% confidence limits]. Renal arginine vasopressin excretion fell significantly after the change from a normal or high to a low sodium diet [2.70 (2.38–8.69) to 2.19 (1.72–4.00) and 3.80 (2.92–5.01) to 2.50 (1.26–2.35) pmol/h, respectively, P <0.05]; in four subjects assayed, plasma atrial natriuretic peptide concentration also fell significantly [20.1 (16.3–24.9)to 13.1 (10.6–16.2) pmol/l, P <0.05]. 4. We conclude that after acute dietary sodium withdrawal: (1) unless enhanced renal sensitivity to aldosterone develops rapidly, increased secretion alone is unlikely to account for the initial decline in renal sodium excretion; (2) decreased atrial natriuretic peptide secretion may have a permissive role in ‘low-sodium’ adaptation; (3) the early ‘low-sodium’ diuresis is probably vasopressin-dependent and is an important mechanism in the preservation of normal plasma osmolality.

1. An oral water load of 20 ml/kg body wt. was given to eight patients with nephrotic syndrome before and after remission of the syndrome, and to 13 healthy control subjects. Urine volume ( D ), free water clearance ( C water ), plasma concentrations of arginine vasopressin (AVP), angiotensin II (ANG II) and aldosterone (Aldo), were determined before and three times during the first 4 h after loading. 2. D and C water increased to a significantly lower level ( P < 0.01) after water loading in patients with nephrotic syndrome than in control subjects, but D and C water were normal after remission of the syndrome. The maximum increase in C water (ΔC water max. ) was 1.07 ml/min (median) before remission and 7.93 ml/min after, compared with 8.01 ml/min in the control group. 3. Creatinine clearance ( C cr ) increased significantly after remission (63 ml/min to 88 ml/min, P < 0.01), and the fractional excretion of sodium was enhanced. AVP was higher in the nephrotic syndrome both before (2.9 pmol/l) and after remission (2.9 pmol/l) compared with the control group (1.8 pmol/l). ANG II and Aldo did not change after remission and remained at the same level as in the control group. 4. The elevation in ΔC water max after remission was accompanied by an increase in C cr in all patients and ΔC water max. and C cr were significantly correlated (ρ = 0.600, n = 16, P < 0.05). No relationship was found between the change in Δ C water max. and ANG II and Aldo. 5. AVP was significantly suppressed in patients with nephrotic syndrome before remission, but not after remission nor in control subjects, so that although AVP did not differ in nephrotic patients before and after remission, AVP cannot be excluded as a contributory factor to the reduction in C water in the nephrotic syndrome. 6. It is concluded that patients with nephrotic syndrome excrete an oral water load slower than control subjects and that the excretion rate is normal after remission of the syndrome. It is suggested that the normalization of C water may be attributed to an increase in glomerular filtration rate or a decrease in proximal tubular sodium reabsorption, although a possible role for AVP has not been excluded.

1. The pressor responses in the pithed rat to α-adrenoceptor agonists can be modified by alterations in arterial blood gas levels or by drugs which interfere with excitation-contraction coupling processes in the vascular smooth muscle, e.g. Ca 2+ -entry blockers or angiotensin converting enzyme (ACE) inhibitors. However, the extent of these influences depends on which agonist is used. 2. The pressor response to intravenous injection of α-adrenoceptor agonists consists of two phases: an initial rapid but transient response (phase I) is followed by a response of slower onset but longer duration (phase II). We have examined the effects of manipulation of arterial blood gases, a Ca 2+ -entry blocker, nifedipine, and an ACE inhibitor, teprotide, on the pressor responses to a series of α-adrenoceptor agonists. In each case, the effects showed selectivity for one or other of the two phases and the differences in susceptibility between agonists could be explained by the relative sizes of the two phases in their responses. In general, phase II was more susceptible to alkalosis, nifedipine and teprotide, so that drugs in which this component predominated were more susceptible to these factors. In contrast there was no direct correlation with the receptor subtypes activated by the agonists. 3. The results are discussed in relation to the modulation of adrenergic responses by physiological factors and drugs which disturb them.

1. Plasma renin reactivity (PRR) is the rate of angiotensin I production after addition of renin to plasma, minus endogenous renin activity. PRR is increased in plasma of patients with renal failure compared with that of normal subjects. The present study was carried out to determine if increased PRR in uraemic plasma is related to differences of endogenous active or inactive renin, endogenous renin substrate, or pH of the incubation in vitro. 2. PRR in plasma of ten uraemic patients was greater ( P <0.02) than that in plasma of ten normal subjects in incubations carried out at pH 7.4 and 5.7. 3. Increased PRR was not accounted for by differences of endogenous active and inactive renin activity. 4. After addition of renin, renin concentration (measured by direct radioimmunoassay) did not differ in normal and uraemic plasma. 5. Renin substrate concentration, measured both indirectly and by direct radioimmunoassay, also did not differ in normal and uraemic plasma. 6. Increased PRR in uraemic plasma is not related to alterations of renin or renin substrate concentrations. These observations are consistent with our earlier hypothesis that there is a deficiency of a renin inhibitor in uraemic plasma.

1. The systemic circulation at rest and during exercise was studied in ten normal male volunteers, after placebo on one occasion and after acute intravenous administration of the serotonergic antagonist ketanserin on another occasion. The effects of ketanserin on the components of the renin—angiotensin—aldosterone system, on plasma catecholamines and on exercise capacity for graded uninterrupted exercise were also investigated. 2. At rest in recumbency rapid intravenous injection of 10 mg of ketanserin, followed by a continuous infusion of 2 mg/h, produced an acute but transient fall in mean intra-arterial pressure of 6 mmHg compared with placebo. After 15 min the mean arterial pressure with ketanserin was within 2 mmHg of the mean pressure with placebo. In the sitting position both at rest and up to 30% of maximal work rate, the mean arterial pressure during ketanserin did not differ from the pressure on placebo. However, at higher levels of physical activity the rise in mean arterial pressure was lower with ketanserin; the pressure achieved with placebo was 7.5 mmHg higher at maximal work rate. Heart rate and cardiac output were significantly higher during ketanserin. 3. When the subjects were lying down and resting, plasma noradrenaline and adrenaline levels, plasma renin activity and angiotensin II concentration were not affected by ketanserin; however, these values were higher in the sitting position both at rest and during exercise. Plasma aldosterone was reduced by ketanserin during exercise and also when the subject was resting in the recumbent position. 4. Exercise capacity as measured by peak oxygen uptake was similar during ketanserin (3.09 ± se 0.12 litres/min) and during placebo (3.11 ± 0.13). 5. The data suggest that 5-hydroxytryptamine can have only a small role, if any, in pressure homoeostasis in sodium replete man at rest in recumbency. At moderate and heavy levels of exercise, the results are compatible with a role for 5-hydroxytryptamine in pressure regulation. Activation of the sympathetic nervous system by ketanserin is suggested by increases of plasma catecholamines, heart rate, cardiac output and plasma renin. The suppression of plasma aldosterone suggests that 5-hydroxytryptamine may have a role in the regulation of aldosterone secretion which is independent of angiotensin II.

1. Systemic, humoral and renal responses to isotonic volume expansion (1800 ml in 3 h) were assessed in normal subjects and patients with normal renin essential hypertension before and during captopril administration. 2. Essential hypertensive subjects had a greater natriuretic and diuretic response to volume expansion than had normotensive subjects. 3. Captopril induced a fall in pre-saline mean arterial pressure more marked in hypertensive (20 ± 3 mmHg) than in normotensive subjects (9 ± 2 mmHg) and did not produce any change in sodium balance. 4. Captopril exaggerated the response of arterial pressure to volume expansion since mean arterial pressure increased more markedly after than before captopril in both normotensive (18.7 ± 3.8%) and hypertensive subjects (16.9 ± 3.7%). 5. Captopril blunted the exaggerated natriuretic response to volume expansion observed in patients with essential hypertension, whereas the renal response was unchanged in normotensive subjects.

1. The role of prostaglandins and angiotensin II in blood flow regulation was studied in conscious rabbits subjected to mild haemorrhage. 2. Haemorrhage caused a 13% fall in arterial pressure and a 21% fall in cardiac output, responses which were unchanged by sodium meclofenamate, an inhibitor of prostaglandin synthesis, or captopril, an inhibitor of the angiotensin converting enzyme. 3. Haemorrhage doubled plasma adrenaline and noradrenaline levels. Plasma renin activity trebled after haemorrhage and was further elevated by captopril. 4. Renal blood flow was maintained after haemorrhage alone. Meclofenamate given immediately after haemorrhage caused a 31% fall in renal blood flow. Captopril given immediately after haemorrhage caused renal vasodilation, but when given after meclofenamate augmented renal vasoconstriction. 5. Splenic vasoconstriction was seen after haemorrhage and meclofenamate, and subsequently was augmented by captopril. 6. Results suggest that prostaglandins variably modulate regional blood flow in conscious rabbits subjected to mild haemorrhage. Enhanced sympathc—adrenal activity increases reno-vascular and splenic dependence on vasodilator prostaglandins, but not that of coronary, cerebral, hepatic or adrenal circulations. Renal and splenic vasoconstriction seen with meclofenamate are not due to circulating angiotensin II.

1. Plasma cortisol at 08.00 hours was significantly higher ( P < 0.005) in patients with high-renin essential or renovascular hypertension (22.6 ± 1.6 μg/100 ml) than in patients with normal-renin (15.4 ± 1.2) or low-renin (11.9 ± 1.2) forms of hypertension. 2. Plasma cortisol at 12.00 or 16.00 hours did not differ significantly among the three groups; thus the diurnal swing in plasma cortisol was steepest in patients with high plasma renin. 3. Among all patients studied, there was a direct relationship between 08.00 hours plasma cortisol and ambulatory plasma renin activity ( r = 0.65, P < 0.001). 4. In patients with high-renin values, 08.00 hours plasma cortisol fell by 39 ± 6% after 10 days treatment with the converting enzyme inhibitor captopril. No consistent decreases were observed in the normal- or low-renin groups. 5. We conclude that the renin—angiotensin system may interact with the pituitary—adrenal axis to influence circulating levels of cortisol. This effect might conceivably contribute to the pathogenesis of certain high-renin states.

1. Systemic, humoral and renal responses to isotonic volume expansion (1800 ml in 3 h) were assessed in normal subjects before and during captopril administration. 2. Captopril, which otherwise induced a decrease in pre-saline mean arterial pressure (MAP), unmasked the volume-dependence of MAP, which increased linearly during volume expansion (+ 18.7 ± 3.8% at the end of volume expansion). 3. Captopril prevented the fall in plasma aldosterone produced by volume expansion but did not modify the natriuretic response to saline. 4. These results suggest that intrarenal rather than circulating angiotensin II may be one of the determinants of the natriuretic response to volume expansion in normal man.

1. Nuclei were isolated from rat liver and spleen by a standard technique which preserved the nuclear membrane. Electron microscopy, DNA/protein ratios and 5′-nucleotidase determinations confirmed the purity of the preparation. 2. Both liver and spleen nuclei specifically bound 125 I-labelled angiotensin II (ANG II) with high affinity ( K d ≅ 1.0 nmol/l). Saralasin ANG III and ANG II competed with tracer for ligand whereas ANG I did so less effectively and neurotensin not at all. 3. These results suggest the presence of specific nuclear intracellular ANG II receptors and raise important questions regarding the mechanism of action of this peptide.

1. Angiotensin-converting enzyme (ACE) activity was threefold greater in isolated cerebral microvessels obtained from rabbit brain than rat brain. 2. ACE activity was distributed throughout the cerebral microvasculature, since differences were not found between preparations enriched in capillaries as compared with those enriched in arterioles and venules. 3. Aortic tissue from rat and rabbit had little ACE activity compared with the microvessels. 4. ACE activity was tightly associated with endothelial cells and was not released by heparin under conditions where lipoprotein lipase was effectively removed.

1. The pressor and heart rate response to angiotensin II, noradrenaline, isoprenaline, tyramine and β-phenylethylamine were examined before and after bile-duct ligation in conscious trained dogs. 2. The pressor response to angiotensin II was markedly suppressed after bile-duct ligation, although responses to noradrenaline and the indirectly acting sympathomimetic amines were only slightly reduced. 3. Bradycardia, in response to the pressor drugs, and tachycardia, in response to isoprenaline, were unchanged after bile-duct ligation. 4. Refractoriness to the pressor action of angiotensin after chronic bile-duct ligation in the present study is similar to that reported previously by others in patients with liver cirrhosis. 5. No evidence was found in the bile-duct ligated dog to support a role of false neurotransmitters as mediators of the circulatory disturbances associated with liver injury.

1. Successive infusions of SQ 20 881 given intra-arterially (i.a.) to the kidney at 0.4 and 0.8 μg min −1 kg −1 for 50 min each did not alter renal blood flow and renal vascular resistance in spite of 40–47% blockade of the angiotensin I (ANG I i.a.)-induced vasoconstrictor response. 2. SQ 20 881 administered intravenously (i.v., 0.5 mg/kg) after the higher intra-arterial dose did not further decrease the renal response to ANG I (i.a.), but caused an increase in renal blood flow and a decrease in renal vascular resistance. 3. These results indicate that SQ 20 881 has limited efficacy in blocking the renal response to ANG I (i.a.). Under the conditions of these experiments, the renal vasodilator response to SQ 20 881 appears to be due to inhibition of extrarenal rather than intrarenal converting enzyme.

1. Angiotensin-converting enzyme inhibitors can attenuate reflex sympathetic vasoconstriction in vivo. We have investigated the effects of captopril (SQ 14 225) on adrenergic vasoconstrictor mechanisms in isolated, Krebs-Ringer solution perfused, rat mesenteric arteries. 2. Low concentrations of captopril (2 × 10 −6 mol/l) did not alter the vasoconstrictor response evoked by sympathetic nerve stimulation. 3. Exogenous angiotensin I and II did not have a direct vasoconstrictor effect, but caused dose-related increases in the amplitude of responses induced by nerve stimulation. 4. The potentiating effect of angiotensin I was antagonized by captopril (6.7 × 10 −8 –2 × 10 −6 mol/l) and by saralasin (10 −8 mol/l). The potentiating effect of angiotensin II was antagonized by saralasin only. 5. In the absence of exogenous peptides high concentrations of captopril (1 × 10 −4 –3 × 10 −4 mol/l) antagonized vasoconstrictor responses evoked by sympathetic nerve stimulation and exogenous noradrenaline, but not those evoked by potassium chloride. 6. These results indicate that captopril can have two types of inhibitory effect at the adrenergic neuro-effector junction. High concentrations antagonize responses to noradrenaline and nerve stimulation. This effect is independent of peptide hormones and is unlikely to occur in vivo. Lower concentrations block the local vascular conversion of angiotensin I into II. As angiotensin II is an important peripheral amplifier of adrenergic vasoconstriction, this effect will also reduce sympathetic vasoconstrictor tone. This latter interaction could explain the inhibitory effect of converting enzyme inhibitors on sympathetic reflexes.

1. The acute effects of a single oral dose of captopril on blood pressure, pulse rate and circulating levels of angiotensin I (ANG I), angiotensin II (ANG II), renin, bradykinin and catecholamines were studied in three groups: eight normal subjects, six salt-depleted normal subjects and 16 patients with essential hypertension. 2. Captopril treatment did not cause any significant fall in supine blood pressure in salt-replete normal subjects or patients with untreated essential hypertension but was associated with a fall in mean blood pressure from 85 ± 2 to 75 ± 2 mmHg in salt-depleted normal subjects and from 131 ± 7 to 117 ± 5 mmHg in patients with essential hypertension treated with diuretics. There was no change in pulse rate in any group. 3. Hormonal responses to captopril were qualitatively similar in the three groups and consisted of significant falls in ANG II with corresponding increases in ANG I and plasma renin concentration. The changes in plasma renin concentration and ANG I were greater in salt-depleted normal subjects (mean values at 90 min were 1140% and 990% of basal levels respectively) than in salt-replete normal subjects (410%, 190%) and were blunted in patients with essential hypertension (140%, 120%). Blood bradykinin, noradrenaline and adrenaline concentrations did not change after captopril in any group. 4. The parallel fall in blood pressure and ANG II levels in salt-depleted normal subjects is consistent with maintenance of blood pressure by increased levels of ANG II in sodium depletion. 5. The failure of captopril to reduce acutely blood pressure in patients with essential hypertension despite suppression of plasma ANG II and without change in circulating bradykinin confirms that the renin-angiotensin system does not play a primary role in essential hypertension.

1. Renin was measured in individual juxtaglomerular apparatuses before and after acidification in vitro. . 2. Active renin increased with delivery of extra sodium by microperfusion to the macula densa and this increase was similar to that achieved with acidification. 3. In rats pretreated with an inhibitor of protein synthesis active renin increased when extra sodium was delivered to the macula densa. 4. Salt intake changed the amount of renin present in the juxtaglomerular apparatus. In rats on a high salt intake the total renin was low and was all in an active form.

1. The effects of prostaglandin (PG) E 1 , PGE 2 and PGF 2α on plasma renin substrate concentration in rats and renin substrate production by perfused rat liver were investigated. 2. After bilateral nephrectomy, both plasma renin substrate concentration and renin substrate production were remarkably elevated. 3. The increase in plasma renin substrate level and production of renin substrate by the liver after nephrectomy was markedly suppressed by the treatment with PGE 1 or PGE 2 . 4. In contrast PGF 2α had no suppressive effect on renin substrate synthesis. 5. These findings suggest that PGE 1 and PGE 2 might be inhibitory factors in the regulation of renin substrate synthesis.

1. Captopril given for 5 days caused a fall in blood pressure in normotensive subjects. The percentage fall in mean supine pressure was greatest on a low sodium diet (10 mmol/day), 19.6%, least on a high sodium diet (350 mmol/day), 11%, and in between on a normal sodium diet (120 mmol/day), 16.5%. 2. Captopril caused a marked fall in plasma aldosterone in normal subjects on all three sodium intakes. 3. Captopril caused an increase in sodium excretion on the normal (120 mmol/day) and low (10 mmol/day) sodium diet but not the high sodium diet. 4. These results suggest that the renin-angiotensin-aldosterone system is a normal mechanism for maintaining blood pressure and aldosterone secretion in normotensive man. The system may also be involved in the maintenance of sodium balance. 5. These results may lead to a better understanding of the role of the renin-angiotensin-aldosterone system in the maintenance or causation of high blood pressure in essential hypertension.

1. By immunoperoxidase technique, immunoreactive angiotensin II (ANG II) was located in the cell bodies of many magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus and their pathways to median eminence and posterior pituitary gland in the rat. 2. Like vasopressin and its neurophysin, but not oxytocin, ANG II was also found in parvocellular neurons in the suprachiasmatic nucleus. 3. Analysis of these peptides in the same magnocellular neurons reveals that ANG II is localized primarily in vasopressin cells. 4. Like vasopressin and its precursor, ANG II is deficient in homozygous Brattleboro rats with diabetes insipidus. 5. In adrenalectomized rats increases in vasopressin and its neurophysin in median eminence are associated with increases in ANG II. 6. The data suggest that the ANG II demonstrated shares antigenic determinants with the vasopressin precursor, or is regulated in a similar way to vasopressin in the same neurons.

1. To investigate the non-angiotensin effects of converting enzyme inhibition, angiotensin II was infused intravenously at 30 ng/min for 9 days in conscious rats to produce moderate blood pressure elevation. One group was given captopril (SQ 14 225) by gavage (100 mg/kg twice daily) and the other glucose. 2. After 7 days of captopril administration, enzyme blockade was confirmed by a tenfold greater depressor sensitivity to exogenous bradykinin and a markedly decreased plasma angiotensin converting enzyme activity. 3. Mean arterial pressure, heart rate and plasma renin activity were not different between captopril and glucose-treated groups in the presence of angiotensin II. Metabolic studies also revealed no long-term differences in water and food intake, weight change or sodium and potassium metabolism. 4. These findings suggest that, in the presence of angiotensin II, there is no detectable haemodynamic or metabolic effect of converting enzyme inhibition in rats and, therefore, that bradykinin plays little or no role in its long-term antihypertensive action.