This short article provides a comment on the recent letter by G. Bhave regarding our hypothesis paper [ Clinical Science (2018) 132, 2609–2613 ].

Using changes in tissue [Na + ] concentration alone as done with Na + MRI may not accurately quantitate excess tissue Na + , particularly in cellular tissues. However, individually quantitating alterations in tissue Na + and water content as possible with ashing studies may still accurately quantitate excess tissue Na + in these situations. Furthermore, when tissue [Na + ] exceeds plasma [Na + ], excess tissue Na + must be present.

Hypertonic Na + accumulation in peripheral tissues is a recently described phenomenon: it has been associated with ageing, hypertension, diabetes, chronic kidney disease and heart failure, but its clinical meaning has yet to be determined. This concept conflicts with the classic physiological paradigm of constant balance between salt intake and excretion, and its water-independent nature is still a matter of debate. We developed a theoretical model explaining changes in the chemical composition of tissues as a function of extracellular volume fraction and excess extracellular fluid, i.e. oedema. The model suggests that the proportional increase in absolute Na + content and concentration due to different degrees of oedema is higher than the parallel increase in water content, thus making Na + a more sensitive index to detect this oedema. Our model would explain some of the recent findings of high tissue Na + content in pathological conditions. More importantly, it prompts the reappraisal of tissue Na + analysis from being a topic of niche interest to a potential diagnostic tool with broad applicability in the investigation of subclinical systemic and localized oedema.

Current guidelines recommend low dietary salt intake (LDS) in patients with diabetes to reduce blood pressure (BP). However, low salt intake has been associated with higher mortality rates in people with diabetes. Our aim is to examine the effect of angiotensin II receptor blocker (ARB), telmisartan, with and without dietary sodium chloride (NaCl) supplementation, on BP [mean arterial pressure (MAP)], plasma renin activity (PRA), serum aldosterone level and estimated glomerular filtration rate (eGFR) in hypertensive patients with type 2 diabetes. In a randomized, double-blind, placebo-controlled study (RCT), 28 patients with type 2 diabetes, treated with telmisartan (40 mg daily), received 2 weeks of placebo or NaCl capsules (100 mmol/24 h). Following a 6-week washout, the protocol was repeated in reverse. Twenty-four-hour urinary sodium excretion (24hUNa), ambulatory BP (ABP) monitoring and blood tests were performed before and after each study phase. The telmisartan-associated increase in PRA was blunted by approximately 50% during salt supplementation compared with placebo; median PRA was 2.3 μg/l/h with placebo compared with 1.7 μg/l/h with salt ( P <0.001). A trend towards blunting of ARB induced increases in serum aldosterone was also demonstrated. Salt supplementation significantly reduced the MAP lowering effects of telmisartan ( P <0.05). The present study demonstrates that salt supplementation blunts the telmisartan induced increase in PRA in patients with type 2 diabetes.

HBP (high blood pressure) is the leading risk of death in the world. Unfortunately around the world, blood pressure levels are predicted to become even higher, especially in developing countries. High dietary salt is an important contributor to increased blood pressure. The present review evaluates the association between excess dietary salt intake and the importance of a population-based strategy to lower dietary salt, and also highlights some salt-reduction strategies from selected countries. Evidence from diverse sources spanning animal, epidemiology and human intervention studies demonstrate the association between salt intake and HBP. Furthermore, animal studies indicate that short-term interventions in humans may underestimate the health risks associated with high dietary sodium. Recent intervention studies have found decreases in cardiovascular events following reductions in dietary sodium. Salt intake is high in most countries and, therefore, strategies to lower salt intake could be an effective means to reduce the increasing burden of HBP and the associated cardiovascular disease. Effective collaborative partnerships between governments, the food industry, scientific organizations and healthcare organizations are essential to achieve the WHO (World Health Organization)-recommended population-wide decrease in salt consumption to less than 5 g/day. In the milieu of increasing cardiovascular disease worldwide, particularly in resource-constrained low- and middle-income countries, salt reduction is one of the most cost-effective strategies to combat the epidemic of HBP, associated cardiovascular disease and improve population health.

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.

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.

The increase in the intracellular Na + concentration ([Na + ] i ) during myocardial ischaemia is crucial for ischaemia/reperfusion cell injury, and the cardiac subtype of the Na + /H + exchanger (NHE-1) has been shown to be a major pathway for Na + loading. While the importance of glycolytically derived ATP for the optimal functioning of membrane transporters and channels has been suggested, whether NHE-1 is actually activated during myocardial ischaemia remains controversial. Here we examined whether the activity of NHE-1 is predominantly dependent on intracellular ATP generated by glycolysis, and whether the additional inhibition of glycolysis can affect the increase in [Na + ] i during the inhibition of oxidative phosphorylation in intact guinea pig ventricular myocytes. The selective inhibition of glycolysis by 2-deoxyglucose prevented the recovery of intracellular pH and the transient increase in [Na + ] i following intracellular acidosis induced by a NH 4 Cl pre-pulse. During severe metabolic inhibition (SMI; induced by amobarbital and carbonyl cyanide m-chlorophenylhydrazone in a glucose-free perfusate), most myocytes changed from rod-shaped to contracted forms by ~ 15 min. [Na + ] i increased linearly until rigor contracture occurred, but after rigor contracture the rate of increase was blunted. The increase in [Na + ] i during SMI was suppressed significantly by an inhibitor of NHE-1, hexamethylene amiloride. The increase in the intracellular Mg 2+ concentration, which can reciprocally indicate depletion of intracellular ATP, was small during the initial 10 min of SMI, but became larger from just a few minutes before rigor contracture. In the presence of 2-deoxyglucose, the time to rigor during SMI was shortened, but the increase in [Na + ] i before rigor contracture was not significant, and was much less than that in the absence of 2-deoxyglucose. It is concluded that ATP generated by glycolysis is essential to activate NHE-1, and that the dependence of NHE-1 on glycolysis might affect the increase in [Na + ] i observed during myocardial ischaemia.

The benefits of tailoring therapy with vasodilators in patients with severe heart failure are well documented, but this may lead to neurohormonal activation and sodium retention. Renal dopamine has local natriuretic actions and interacts with other hormones involved in renal sodium handling. The aim of the present work was to determine the effects of arterial underfilling induced by vasodilator therapy on renal sodium handling, neurohormonal activation and the activity of the renal dopaminergic system in patients with severe heart failure. For this purpose we monitored haemodynamic parameters, plasma levels of type B natriuretic peptide (BNP), catecholamines, aldosterone, renin activity (PRA), sodium and creatinine, and urinary excretion of sodium, creatinine, l -DOPA, dopamine and its metabolites, before initiation of sodium nitroprusside therapy and every 6 h thereafter (for 42 h), and again after 5 days of angiotensin-converting enzyme (ACE) inhibition, in 10 male patients with severe heart failure. The results of nitroprusside therapy were a marked increase in cardiac index and a substantial decrease in systemic vascular resistance index. Plasma levels of BNP decreased significantly, while PRA, noradrenaline and aldosterone showed marked increases, resulting in a substantial reduction in urinary sodium excretion. Creatinine clearance was not affected. Urinary dopamine and dopamine metabolites increased in response to nitroprusside therapy. After 5 days of ACE inhibition, urinary sodium returned to baseline values, while urinary dopamine was markedly reduced. These results suggest that the renal dopaminergic system is activated in patients with severe heart failure by stimuli leading to sodium renal reabsorption.

The purpose of the present study was to evaluate prospectively blood pressure and the renal haemodynamic response to salt during the normal menstrual cycle. A total of 35 healthy normotensive young women not on oral contraceptives were enrolled; 17 were studied in the follicular phase and 18 in the luteal phase of the menstrual cycle. The women in each group were then randomly allocated to receive a low-sodium (40 mmol/day) or a high-sodium (250 mmol/day) diet for a 7-day period in two consecutive menstrual cycles. At the end of each dietary period, 24 h ambulatory blood pressure, urinary sodium excretion, plasma renin activity, plasma catecholamine levels and renal haemodynamics were measured. Our results show that the blood pressure response to salt is comparable during the luteal and the follicular phases of the normal menstrual cycle and is characterized by a salt-resistant pattern. In the kidney, effective renal plasma flow was significantly greater and the filtration fraction lower ( P < 0.05) after salt loading in women studied in the luteal phase compared with women investigated in the follicular phase. This study thus demonstrates that the female hormone status does not affect the blood pressure response to sodium in young normotensive women. However, in contrast with systemic haemodynamics, the renal response to salt varies during the normal menstrual cycle, suggesting that female sex hormones play a role (direct or indirect) in the regulation of renal haemodynamics.

The effect of a continuous infusion of human brain natriuretic peptide, 2 ;pmol·min -1 ·kg -1 , during 60 ;min was studied in nine patients with congestive heart failure and in 10 healthy control subjects. Brain natriuretic peptide increased from 1.6 to 101 ;pmol/l in control subjects and from 25 to 173 ;pmol/l in congestive heart failure during infusion. Urinary sodium excretion increased significantly in both congestive heart failure (60%) and control subjects (71%), but the absolute increase was significantly lower in congestive heart failure (27 ; μ mol/min) than in control subjects (190 ; μ mol/min). Urinary flow rate did not change. The lithium clearance technique was used to evaluate the segmental tubular function; the distal fractional reabsorption of sodium decreased significantly less in congestive heart failure (DFR Na : -0.8%) than in control subjects (DFR Na : -3.7%). Baseline values for glomerular filtration rate and renal plasma flow were reduced in congestive heart failure, but brain natriuretic peptide induced no significant changes between congestive heart failure and control subjects. Brain natriuretic peptide induced the same absolute increase in secondary messenger cGMP in plasma and urine in both patients and healthy subjects. It is concluded that the natriuretic response to brain natriuretic peptide infusion was impaired in patients with congestive heart failure compared with healthy subjects, and it is likely that the impaired natriuretic response was caused by a reduced responsiveness in the distal part of the nephron.

1. Although in blood cells decreased magnesium concentrations and increased sodium concentrations in essential hypertension have often been described, only sparse data exist on cellular magnesium or sodium content and exchange in vascular smooth muscle cells. 2. Therefore in aortic smooth muscle cells from 10 spontaneously hypertensive rats (SHR) of the Münster strain and 10 normotensive Wistar–Kyoto rats (WKY) aged 3 and 8–10 months, the intracellular magnesium and sodium content was measured. 3. Electron-probe X-ray microanalysis was used to determine intracellular Mg 2+ and Na + concentrations in aortic cryosections 3 ; μ m thick. The Mg 2+ content was 47±13 ;mmol/kg dry weight in SHR versus 48±19 ;mmol/kg dry weight in WKY aged 3 months, and 37±6 ;mmol/kg dry weight in SHR versus 47±4 ;mmol/kg dry weight in WKY aged 8–10 months ( P < 0.05). Vascular smooth muscle Na + content was 283±59 ;mmol/kg dry weight in WKY and 402±123 ;mmol/kg dry weight in SHR aged 3 months ( P < 0.05), and 289±17 ;mmol/kg dry weight in WKY versus 548±39 ;mmol/kg dry weight in SHR aged 8–10 months ( P < 0.05). 4. Aortic smooth muscle cells from SHR are characterized by a markedly lower intracellular Mg 2+ content in 8–10-month-old animals and increased Na + concentrations compared with normotensive cells in 3- and 8–10-month-old rats. The results may be due to genetically determined disturbances in transmembrane Mg 2+ and Na + transport. Cellular magnesium and sodium handling may be disturbed in SHR aortic smooth muscle as it is in hypertensive blood cells. In addition, it is concluded that vascular smooth muscle cell Mg 2+ –Na + exchanger can be altered in a subgroup of SHR.

1. The Na + ,K + -ATPase or Na + ,K + -pump, mediating the active transport of Na + and K + , which was first identified 40 years ago, is a central target for acute and long-term regulation, as well as for therapeutic intervention. Acute stimulation of the Na + ,K + -pump in skeletal muscle by insulin, catecholamines, β 2 -agonists or theophylline increases the intracellular uptake of K + and accounts for the hypokalaemia elicited by these agents. Conversely, digitalis intoxication elicits hyperkalaemia via acute inhibition of the Na + ,K + -pump. 2. Simple and accurate methods have been developed for the quantification of the total concentration of Na + ,K + -pumps in small (0.5–5 mg) fresh or frozen biopsies of human skeletal muscle, myocardium or other tissues. This has allowed the identification of several long-term regulatory changes in the concentration of this transport system in human tissues. In skeletal muscle, upregulation is induced by training, thyroid hormones or glucocorticoids. Downregulation is seen in hypothyroidism, cardiac insufficiency, myotonic dystrophy, McArdle disease, K + deficiency and after muscle inactivity. 3. Since the skeletal muscles contain one of the major pools of Na + ,K + -pumps, these changes are important for the ability to counterregulate the hyperkalaemia elicited by exercise or the ingestion of K + . Moreover, downregulation or inhibition of the Na + ,K + -pumps in skeletal muscle interferes with contractile performance. Since digitalis glycosides bind to the Na + ,K + -pump, the muscles constitute a large distribution volume for these agents and are therefore an important determinant for their plasma level. 4. In cardiac insufficiency, the decrease in the concentration of Na + ,K + -pumps in the myocardium is over a wide range correlated to the concomitant reduction in ejection fraction. The regulatory and pathophysiological changes in the activity and concentration of Na + ,K + -pumps are important for the contractile function of skeletal muscle and heart as well as for K + homoeostasis and the response to digitalization.

1. The behaviour of the potent vasoconstrictive endothelium-derived peptide endothelin-1 was evaluated in salt-sensitive hypertension. 2. Circulating and urinary endothelin-1 levels were evaluated in 30 men (mean age 44.6 ± 3.1 years) with uncomplicated essential hypertension after three consecutive 2-week periods on an intermediate (120 mmol), low (20 mmol) and high (240 mmol) NaCl diet. On the same occasions, blood pressure was measured to identify salt-sensitive patients ( n = 16), i.e. those patients showing a mean blood pressure increase > 10 mmHg when switching from a low to a high NaCl diet, and salt-resistant patients ( n = 14), i.e. those who did not show such mean blood-pressure variations. 3. Plasma endothelin-1 levels were higher ( P < 0.005) in salt-sensitive than in salt-resistant hypertensive patients after intermediate-, low- and high-NaCl diets. Urinary endothelin-1 excretion was similar in both groups after an intermediate-NaCl diet, whereas it was significantly higher in salt-sensitive than in salt-resistant hypertensive subjects after low ( P < 0.002) and high ( P < 0.007) NaCl diets. High NaCl intake induced a significant increase in plasma endothelin-1 levels ( P < 0.002) as compared with intermediate and low NaCl diet levels in salt-sensitive patients, but did not in salt-resistant subjects. No significant NaCl intake-related variations of urinary endothelin-1 excretion were observed in either group. 4. Salt-sensitive hypertensives are characterized by increased levels of endothelin-1 in both plasma and urine. This fact suggests that blood-pressure sensitivity to NaCl intake could be associated with an increased risk of developing both renal and cardiovascular damage.

1. The renal efficacy of urodilatin in humans has only been partly investigated. It is unknown whether intravenously infused urodilatin has an effect on sodium reabsorption in both the proximal and distal part of the nephron. 2. Twelve healthy subjects participated in this double-blind, placebo-controlled study in a crossover design. They received, in a randomized order, a short term (60 min) infusion of urodilatin in three different doses (10, 20 and 40 ng min −1 kg −1 of body weight) and placebo. Renal haemodynamics were estimated by clearance technique with radioactive tracers, and proximal tubular handling of sodium was evaluated by lithium clearance. 3. The 20 ng min −1 kg −1 dose increased the urinary sodium excretion and urinary flow rate compared with the effects of placebo. It increased the glomerular filtration rate and decreased the effective renal plasma flow. In addition, the dose increased the lithium clearance compared with placebo, but did not significantly change the fractional excretion of lithium. On the other hand, it markedly decreased the distal fractional reabsorption of sodium. It also had a suppressive effect on renin secretion. The systemic arterial blood pressure was unchanged, but the dose increased the pulse rate and the haematocrit. The highest dose (40 ng min −1 kg −1 ) induced a wide variation in the natriuretic and diuretic responses, probably due to a blood-pressure-lowering effect. 4. We conclude, that the urodilatin dose of 20 ng min −1 kg −1 of body weight was most efficacious in this short-term infusion study, and that it had potent natriuretic and diuretic qualities, probably due to stimulation of the glomerular filtration rate and inhibition of sodium reabsorption in the distal part of the nephron.

1. The nephron sites involved in the blunted natriuretic response to frusemide during sodium depletion were investigated using micropuncture techniques in anaesthetized rats. 2. Glomerular filtration rate was lower, and fractional sodium reabsorption in the proximal convoluted tubule higher, in sodium-depleted than in sodium-replete rats. Consequently, sodium delivery to the loop of Henle was reduced (by approximately 35%) in the sodium-depleted animals. Intravenous frusemide (2.5 mg h −1 kg −1 ; urinary water and electrolyte losses replaced) had no effect on glomerular filtration rate or proximal tubular sodium reabsorption in either group. 3. The inhibitory effect of intravenous frusemide on fractional sodium reabsorption in the nephron segments constituting the loop of Henle (measured by free-flow micropuncture) was attenuated during sodium depletion. However, when loops of Henle were microperfused at identical rates with artificial late proximal tubular fluid, no difference in the responses of sodium-depleted and sodium-replete rats to intraluminal frusemide (10 −5 mol/l) could be detected. 4. In sodium-replete animals, the increased load of sodium delivered from the loop of Henle during frusemide administration resulted in a lowering of fractional sodium reabsorption in the distal tubule. In contrast, in sodium-depleted rats given frusemide, fractional distal sodium reabsorption tended to increase, so that values in the two groups of frusemide-treated animals were markedly different (0.30 ±0.04 versus 0.51 ±0.03). 5. It is concluded that the blunted natriuretic response to frusemide during sodium depletion results from at least three factors: a reduced sodium delivery to the loop of Henle; a reduced inhibitory effect of frusemide on fractional sodium reabsorption in the loop of Henle, which may be a consequence of the reduced sodium load; and enhanced fractional reabsorption of sodium in the distal tubule, which partially buffers the diuretic-induced increase in sodium delivery from the loop.

1. To clarify the mechanism by which cytosolic free Mg 2+ concentrations ([Mg 2+ ] i ) are regulated in human platelets, we investigated platelet membrane permeability to Mg 2+ by altering extracellular Mg 2+ concentrations, and tested the existence of a Na + -Mg 2+ exchanger by manipulating the transmembrane Na + gradient. 2. Platelet [Mg 2+ ], was 421 ± 52 μmol/l in healthy men. [Mg 2+ ]; remained constant during a 120 min exposure to nominally zero (low) or 5 mmol/l (high) external Mg 2+ concentrations. 3. Preincubation of platelets with 10 −4 mol/l ouabain effectively decreased the transmembrane Na + gradient. The ouabain-induced increase in [Mg 2+ ], was statistically significant after 30 min of exposure (14.6 ± 2.0%) and reached 24.6 ± 4.5% after 60 min. Similarly, the replacement of extracellular Na + with N -methyl-d-glucamine significantly increased [Mg 2+ ] i by 48.5 ± 3.9% and 78.8 ± 12.5%, respectively. 4. These results suggest that [Mg 2+ ] i is well controlled in the presence of large transmembrane Mg 2+ concentration gradients, and a Na + -Mg 2+ exchanger may be involved in the regulation of [Mg 2+ ] i in human platelets.

1. Hyperinsulinaemia is considered to be a pathogenic factor for human and experimental hypertension. Thus, the contribution of the known insulin-stimulated tubular sodium reabsorption to this aetiological process has to be discussed. 2. Rats fed a fructose-enriched diet develop hyperinsulinaemia and hypertension, providing a model for studying the regulation of the tubular sodium handling and its possible relationship to hypertension. For this purpose, the sodium transport capacity of isolated nephron segments from control rats and from rats fed a fructose-enriched diet was investigated by measurement of ouabain-sensitive 86 Rb uptake and of the hydrolytic activity of Na,K-ATPase. The number and affinity of insulin receptors were estimated from the specific [ 125 I]insulin binding. 3. In rats fed a fructose-enriched diet, mild hypertension developed during the 14-day fructose diet. There were no differences, along the nephron, in basal 86 Rb uptakes and ATPase activities between control rats and fructose-induced hypertensive rats. In control rats, insulin stimulated 86 Rb uptake in the proximal convoluted tubule and cortical collecting duct, but exhibited an inhibitory action in the medullary thick ascending limb. In contrast, in fructose-induced hypertensive rats, 86 Rb influx remained unresponsive to insulin concentrations ranging from 10 −11 to 10 −7 mol/l in the proximal convoluted tubule and cortical collecting duct. In the medullary thick ascending limb, the threshold of inhibition was displaced from 10 −11 mol/l up to 10 −7 mol/l. Insulin binding to the proximal convoluted tubule, medullary thick ascending limb and collecting duct were similar in control rats and in rats fed a fructose-enriched diet. 4. We conclude that hypertension developed in rats fed a fructose-enriched diet regardless of change in renal sodium handling since (1) the basal tubular sodium reabsorption capacity of the nephron remained unchanged and (2) the response of the tubular cation transport to insulin was abolished. These results strongly argue against the participation of insulin-mediated tubular sodium retention in the pathogenesis of hypertension and suggest that insulin-related mechanisms modulate the blood vessel reactivity.

1. Recently, we have demonstrated that hypoxic breathing is followed by an increase in plasma digoxin-like substance in normal men. 2. This study was undertaken in order to evaluate whether or not a low arterial O 2 partial pressure is combined with an increase in plasma digoxin-like substance in chronic pathological conditions also. 3. Sixteen male patients (mean age 53.1 ± 3.7 years) affected by chronic obstructive pulmonary disease of a mild stage were studied. They were further subdivided according to their arterial O 2 partial pressure into ‘mild hypoxic’ ( n = 8, mean age 52.5 ± 2.7 years), with an arterial O 2 partial pressure between 66 and 75 mmHg, and ‘severe hypoxic’ ( n = 8, mean age 54.3 ± 5.1 years), with an arterial O 2 partial pressure 65 mmHg, groups. Seven healthy men (mean age 48.5 ± 4.8 years) voluntarily participated as the control group. 4. Plasma digoxin-like substance levels were significantly higher in ‘severe hypoxic’ patients (203.5 ± 9.9 pg/ml) than in both ‘mild hypoxic’ patients (169.5 ± 31.4 pg/ml, P < 0.02) and normal subjects (158.9 ± 12.4 pg/ml, P < 0.0001) and were directly correlated with urinary Na + excretion (severe hypoxic group, r = 0.756, P < 0.007; mild hypoxic group, r = 0.789, P < 0.02). Considering the two hypoxic groups together, plasma digoxin-like substance levels were negatively correlated with arterial O 2 partial pressure ( r = −0.740, P < 0.001). However, when patients were subdivided according to the degree of hypoxia, the negative correlation between arterial O 2 partial pressure and plasma digoxin-like substance persisted only in severe hypoxic patients ( r = −0.761, P < 0.03). 5. These results indicate a clear linkage between blood O 2 and endogenous digoxin-like substance regulation. In particular, hypoxia may be regarded as an important stimulus for the release of the endogenous digoxin-like substance in man.

1. Pre-eclampsia is characterized by reduced plasma active renin concentration and renal prostacyclin production. The aim of this study was to determine whether the plasma active renin concentration could be stimulated in women with pre-eclampsia by intravenous frusemide, which stimulates renin acutely through a prostacyclin-mediated mechanism. 2. Plasma active renin concentration, plasma aldosterone concentration, haematocrit and urinary sodium, creatinine and 6-keto-prostaglandin F 1α were measured before (0) and 15, 30 and 60 min after intravenous frusemide in 10 non-pregnant women, 10 normal pregnant women and nine women with pre-eclampsia. Six normal pregnant and six non-pregnant women underwent the same measurements after injection of 2ml of saline to control for effects of time and posture. 3. Baseline plasma active renin concentration (but not plasma aldosterone concentration) was lower in pre-eclamptic women [4.0 (1.7–6.2) pmol of angiotensin I h −1 ml −1 ; median (interquartile range)] than in normal pregnant women [6.7 (5.3–12.2) pmol of angiotensin I h −1 ml −1 ] ( P < 0.05). Baseline urinary 6-keto-prostaglandin F 1α /creatinine ratio, urinary sodium excretion and fractional sodium excretion did not differ between normal pregnant and pre-eclamptic women. 4. After frusemide, plasma active renin concentration rose significantly in non-pregnant ( P = 0.002) and normal pregnant ( P = 0.008) women, but not in women with pre-eclampsia. Individual results showed stimulation in all non-pregnant and normal pregnant women but in only six out of nine pre-eclamptic women, significantly fewer than in normal pregnancy ( P < 0.05). The overall magnitude of the response of plasma active renin concentration to frusemide was blunted significantly in pre-eclamptic compared with normal pregnant women ( P = 0.022). 5. Absolute and fractional sodium excretion and haematocrit rose significantly in all groups and the magnitude of change did not differ among groups for any of these parameters. The urinary 6-keto-prostaglandin F 1α /creatinine ratio increased significantly only in non-pregnant women ( P = 0.01), with variable individual responses in normal and hypertensive pregnant women. 6. This study shows that normal pregnant women exhibit natriuresis and stimulation of plasma renin after frusemide similar to that of non-pregnant women. However, pre-eclamptic women, as a group, have impaired renin stimulation after frusemide but a similar natriuresis to that of normal pregnant women. The mechanisms of these changes are unclear but are consistent with the notion of ‘exhausted’ renal renin in some women with pre-eclampsia.

1. Diabetes mellitus is associated with high body sodium, but the pathogenetic mechanism is still unknown. The possibility that an abnormal renal handling of sodium, an abnormal responsiveness of sodium-modulating factors or a shift in the set point for sodium metabolism may contribute to or be associated with sodium retention was tested with an acute saline infusion. 2. A consecutive sample of 33 patients with stable non-azotaemic diabetes mellitus (24 insulin-dependent patients) and 30 normal control subjects was studied. Two litres of a 0.9% NaCl infusion were infused over 4 h. The urinary sodium excretion during the infusion and the next 18 h was analysed in relation to blood pressure, creatinine and lithium clearances, Na + −K + co-transport, Na + −Li + countertransport, plasma levels of renin, angiotension II, aldosterone, noradrenaline, adrenaline, atrial natriuretic factor and digoxin-like factor. 3. Diabetic patients and control subjects did not differ in blood pressure, body mass index, clearances of creatinine, sodium or lithium, intracellular sodium, Na + −K + co-transport and Na + −Li + countertransport, urinary and plasma levels of digoxin-like factor, plasma renin activity, angiotensin II, aldosterone, noradrenaline, adrenaline and atrial natriuretic factor. The intravenous saline infusion caused a similar natriuresis in diabetic patients and normal subjects; the renin—angiotension-aldosterone system was suppressed to a higher degree in diabetic patients than in normal subjects, whereas atrial natriuretic factor was stimulated to a similar extent; plasma digoxin-like activity was unchanged in both groups. 4. The natriuretic response to saline infusion was comparable between patients with insulin-dependent and non-insulin-dependent diabetes mellitus, those with lower or higher HbA1c levels and those with positive or negative family history of essential hypertension. 5. Using an acute saline infusion to study sodium-modulating factors, no abnormality can be detected which could represent a pathogenetic mechanism for sodium retention in diabetes mellitus. The normal natriuretic response to acute sodium loading in diabetic patients indicates that the set point for sodium homoeostasis may be normal despite the presence of high exchangeable sodium.

1. The purpose of the present study was to examine the effects of various diuretics on intestinal oxalate transport. Transmural oxalate fluxes were measured across isolated, short-circuited tissue segments removed from rabbits and placed in Ussing chambers. 2. The net absorptive flux of oxalate across the distal colon was significantly reduced in the presence of trichlormethiazide at 10 −4 mol/l. In contrast, this diuretic had no effect on oxalate transport in the other intestinal segments examined. Several of the thiazide diuretics tested had some inhibitory effect on colonic oxalate absorption, but at higher concentrations of 10 −3 mol/l or 10 −2 mol/l. 3. We conclude that the previously reported hypooxaluric effects of hydrochlorothiazide and chlorthalidone are most likely not the result of an exclusive or primary effect on intestinal oxalate transport. It is suggested that the reduction in colonic oxalate absorption that was observed with the thiazides probably involves the transport system responsible for oxalate efflux across the basolateral membrane of the colonocyte.

1. The present study was designed to investigate the relationships between circulating atrial natriuretic peptide, plasma and urinary cyclic GMP and sodium excretion under basal conditions and in response to changes in dietary sodium intake. 2. Measurements of plasma atrial natriuretic peptide and plasma and urinary (24 h collections) cyclic GMP, sodium and creatinine were made in (i) 30 normotensive subjects on their normal sodium intake and (ii) 12 subjects on the 5th day of a low and on the 5th day of a high sodium intake. 3. Plasma cyclic GMP, urinary cyclic GMP and fractional excretion of cyclic GMP in 30 normotensive subjects on their normal sodium intake were (means ± SEM) 5.4 ± 0.5 pmol/ml, 434.5 ± 31.8 pmol/min and 86.9 ± 8.6%, respectively. There were significant correlations between urinary cyclic GMP and its corresponding filtered load ( r = 0.55) and between the renal clearance of cyclic GMP and that of creatinine ( r = 0.44), but there were no significant associations between circulating atrial natriuretic peptide and plasma cyclic GMP or the fractional excretion of cyclic GMP or between urinary sodium and the fractional excretion of cyclic GMP. 5. Plasma atrial natriuretic peptide was significantly raised on the 5th day of the high sodium intake compared with the low sodium intake (10.6 ± 1.6 versus 4.2 ± 0.9 pg/ml; P <0.05). Similarly, there were increases in urinary cyclic GMP excretion (692.3 ± 43.4 versus 427.4 ± 41.9 pmol/min, P <0.05), but there were no significant differences in the fractional excretion of cyclic GMP. 6. As neither plasma nor urinary cyclic GMP was strongly associated with circulating levels of atrial natriuretic peptide, the present study suggests that other factors may be more important than circulating atrial natriuretic peptide as determinants of extracellular cyclic GMP.

Ten years ago the Editorial Board of Clinical Science invited me to write an Editorial Review on dopamine and the kidney. The result was published in 1982 in Volume 62 [1]. It was my hope that it would serve to stimulate other investigators to take up this area of renal physiology and pharmacology and to help to solve some of the problems left unanswered at that time. Since 1982 much has happened: there have been major successes, such as the delineation of the renal and adrenal dopamine receptors, and some relative failures, such as the lack of development of clinically useful peripheral dopamine agonists for use in hypertension and congestive cardiac failure. Nevertheless, continuous progress has been made and it is my task in this Review to try to describe this general advance while not omitting remaining areas of uncertainty. The areas which I will undertake to describe are: 1. The renal receptors for dopamine. 2. The source of dopamine in the urine and its formation in the kidney. 3. The actions of dopamine upon the kidney. 4. The interaction of renal dopamine with other substances. 5. Dopamine formation in hypertensive and oedematous states. 6. The search for specific peripheral dopaminergic agonists of therapeutic utility. 7. Final conclusions and unanswered questions.

1. We have studied the transport of Na + and K + by erythrocytes during the follicular and luteal phases of the human menstrual cycle, and in pregnant compared with non-pregnant women. Venous blood was drawn from 10 healthy young women (not taking any medication or hormones) 1-2 days after menstruation and from the same women 7-9 days after ovulation. For the pregnancy part of the study, blood was drawn from eight other normotensive non-pregnant women and from eight age-matched normotensive pregnant women (36-43 weeks gestation). 2. Intracellular erythrocyte and plasma Na + and K + concentrations were measured by flame photometry. The increase in the intracellular Na + concentration during a 1 h 37°C incubation of fresh whole blood with 0.2 mmol/l ouabain (compared with no ouabain) was measured to determine the rate of active Na + efflux. The Na + -K + pump rate constant was calculated by dividing the active Na + efflux rate by the intracellular Na + concentration. 3. In fresh blood, the intracellular erythrocyte Na + concentration ( P < 0.002) and the plasma K + concentration ( P < 0.01) were both lower in pregnant than in non-pregnant women. The Na + -K + pump rate constant was higher ( P < 0.02) during the luteal phase than during the follicular phase, and in pregnant compared with non-pregnant women. 4. We conclude that short-acting hormones in the plasma most probably account for the changes in the Na + -K + pump rate constant during the menstrual cycle.

1. The effect of a single dose of lithium on renal function before and during intravenous infusion of dopamine (3 μg min −1 kg −1 ) was investigated in 12 healthy males. In a double-blind and randomized design, 450 mg or 600 mg of lithium carbonate or placebo was administered orally at 22.00 hours on three different occasions. After an overnight fast, the subjects were water-loaded and clearance studies were started at 09.00 hours with a 1 h baseline period and three 1 h periods during dopamine infusion. 2. Baseline sodium clearance with placebo was 0.65 ± 0.35 ml/min, but with lithium it increased to 1.25 ± 0.44 ( P < 0.001) and 1.17 ± 0.46 ml/min ( P < 0.01) after 450 and 600 mg, respectively. Urine flow rates were unchanged compared with placebo. Lithium did not significantly affect glomerular filtration rate, but both doses slightly increased effective renal plasma flow by 7% ( P < 0.05) and 10% ( P < 0.01), respectively. 3. The maximal natriuretic and diuretic effects of dopamine were not reduced by lithium, but the percentage increases in sodium clearance were significantly diminished after 450 mg ( P < 0.01) and 600 mg ( P < 0.001) of lithium. Lithium had no effect on dopamine-induced changes in effective renal plasma flow, glomerular filtration rate or osmolal clearance. Neither lithium nor dopamine influenced plasma concentrations of renin, aldosterone or atrial natriuretic peptide. 4. In conclusion, single test doses of lithium, as normally used in lithium clearance studies, increase baseline values of sodium clearance and effective renal plasma flow. Although these effects of lithium do not reduce the maximal renal responses to low-dose dopamine, they result in an underestimation of the percentage increase in sodium excretion.

1. The aim of this investigation was to study the role of prostaglandins in the impaired Na + conservation of the ageing kidney. 2. We measured the urinary excretion of thromboxane B 2 , 6-keto-prostaglandin F 1α and prostaglandin E 2 in young (3–4 months) and old (20–21 months) rats after 12, 24 and 36 h of Na + deprivation. In a separate protocol, we measured prostanoid synthesis by isolated glomeruli, cortical homogenates, medullary slices and papillary slices from young and old rats in basal conditions and after 15 days of dietary Na + deprivation. 3. In the acute study, urinary excretion of 6-ketoprostaglandin F 1α and prostaglandin E 2 decreased in young but not in old rats. Urinary excretion of prostaglandin E 2 was lower in old rats, but did not vary significantly with Na + deprivation. 4. In old rats, thromboxane B 2 synthesis was increased in all the portions of the kidney except the medulla. Production of 6-keto-prostaglandin F 1α was elevated in glomeruli and tended to increase in the cortex. Prostaglandin E 2 synthesis was also elevated in the cortex. Thromboxane B 2 synthesis tended to increase in the medulla and was enhanced in the papilla. After Na + deprivation, only glomerular prostaglandin E 2 synthesis increased in young rats. In old rats, cortical and papillary synthesis of 6-ketoprostaglandin F 1α increased, whereas prostaglandin E 2 synthesis did not change. 5. The results suggest increased thromboxane synthesis in the ageing kidney. Increased prostacyclin and prostaglandin E 2 synthesis may be an attempt to counteract enhanced thromboxane production. Blunting of this tendency in medulla and papilla could contribute to the conservation of medullary solute concentration, whereas inappropriate stimulation of prostacyclin synthesis during Na + deprivation could impair Na + conservation.

1. Increased erythrocyte sodium-lithium countertransport activity has been reported to be associated with nephropathy in type 1 diabetes and linked to a family history of essential hypertension. 2. This study aimed to determine the mechanism of increased sodium-lithium countertransport activity. Sodium-lithium countertransport kinetics were measured in uncomplicated and hyperlipidaemic type 1 diabetic patients. 3. In the nine out of 31 uncomplicated type 1 diabetic patients who had high sodium-lithium countertransport activity, the sodium affinity ( K m ) was normal but the maximum velocity ( V max. ) was increased. 4. Hyperlipidaemia, when present in diabetic patients, was associated with increased sodium-lithium countertransport activity, but could not explain the high activity in uncomplicated type 1 diabetic patients in whom plasma lipid concentrations were normal. 5. Sodium-lithium countertransport activity is increased in type 1 diabetes by a mechanism different to that in essential hypertension, where the mechanism is a low K m (increased sodium affinity). Hence familial hypertension cannot explain the raised sodium-lithium countertransport activity in type 1 diabetes.

1. Sodium pump function has been assessed by measurement of ouabain-sensitive 86 Rb uptake in human erythrocytes after incorporation of palmitic, stearic, oleic and linoleic acids into the erythrocyte membrane. 14 C-labelled fatty acids were used to measure membrane uptake of these substances. 2. For palmitic, oleic and linoleic acids, up to 1000 nmol of the fatty acid/ml of packed cells can be incorporated without causing significant haemolysis. For stearic acid, 270 nmol/ml of packed cells was incorporated in similar conditions. More than 88% of the fatty acid incorporated could be extracted with a 50 μmol/l fatty-acid-free albumin solution and was, therefore, in a non-esterified form in the erythrocyte membrane. The concentrations of palmitic, stearic, oleic and linoleic acids incorporated in these experiments represent a five- to ten-fold increase above the normal concentrations of these fatty acids in the membrane. 3. Up to 1000 nmol of palmitic, oleic and linoleic acids/ ml of packed cells and up to 270 nmol of stearic acid/ml of packed cells could be incorporated without a significant change in mean ouabain-sensitive 86 Rb uptake with respect to control cells. Mean percentage changes in ouabain-sensitive 86 Rb uptake for all these experiments were: palmitic acid, 3.7% ( sd 11.4, n = 15); stearic acid, 4.0% ( sd 5.7, n = 7); oleic acid, −4.8% ( sd 19, n = 17); linoleic acid, 2.2% ( sd 15.6, n = 19). 4. The demonstration of near-normal sodium pump activity in the presence of greatly elevated membrane levels of these fatty acids makes it extremely unlikely that they act as modulators of sodium pump function in vivo.

1. In the nephrotic syndrome the kidneys retain salt and water, which leads to oedema formation. The site of this sodium retention has been localized in the cortical collecting tubule by micropuncture studies. Whether or not this phenomenon is an intrinsic renal problem or is the consequence of changes in hormonal activities is still a matter of discussion. 2. Using the model of puromycin aminonucleoside-induced nephrotic syndrome in the rat, we measured Na + ,K + -ATPase activity in nephron segments from control and nephrotic rats and investigated the regulatory role of aldosterone and endogenous-ouabain-displacing factor. 3. Nephrotic animals had a twofold increase in Na + ,K + -ATPase activity in the cortical collecting tubule only (control versus nephrotic: 1065 ± 68 versus 2081 ± 274 pmol h −1 mm −1 , P = 0.036), which was not modified by adrenalectomy and was independent of the kidney content of endogenous ouabain-displacing factor. Na + ,K + -ATPase activity in the cortical collecting tubule correlated with the sodium balance in both control and nephrotic rats. 4. The data are consistent with the view that sodium retention in this model of the nephrotic syndrome is a primary event, i.e. an increase in sodium transport throughout the cortical collecting tubule expressed as a twofold increase in Na + ,K + -ATPase activity which is no longer under hormonal regulation (aldosterone and endogenous ouabain-displacing factor).

1. Na + /H + antiport activity was measured in peripheral blood polymorphonuclear and mononuclear cells of 12 healthy subjects by using an intracellular pH clamp technique to determine the external Na + -dependent H + efflux rate in cells loaded with a pH-sensitive fluorescent dye, bis(carboxyethyl)carboxyfluorescein. The change in external Na + concentrations for all pH measurements was similar in both cell types. 2. A significant difference between the two types of cells was found, the polymorphonuclear leucocytes having a higher Na + /H + antiport activity than the lymphocytes. Cellular intrinsic buffering capacity measured in the absence of HCO − 3 was also higher in the polymorphonuclear cells than in the lymphocytes. 3. These differences may be associated with a difference in the role of the Na + /H + exchanger in these two types of cells, although in vivo the presence of HCO − 3 /Cl − exchangers may also contribute to intracellular pH homoeostasis.

1. Normotensive primigravid pregnant women were studied longitudinally during pregnancy and 20 weeks after delivery. 2. Erythrocyte sodium content, ouabain-sensitive sodium flux and sodium pump rate constant were measured in whole blood, and the maximum velocity and sodium affinity of the sodium pump were measured in vitro. 3. Erythrocyte sodium content decreased and the sodium pump rate constant increased up to 26 weeks gestation. The increase in rate constant was due to an increase in the affinity of the sodium pump for sodium up to 20 weeks gestation. After 20 weeks gestation there was an increase in maximum velocity and a decrease in sodium affinity of the sodium pump but no further change in the sodium pump rate constant. 4. At 14 weeks gestation the sodium pump rate constant was correlated with both the maximum velocity and sodium affinity constant. After this time the relationship was much more variable and there was no correlation with the sodium affinity constant. The comparison of measurements of the sodium pump in whole blood and in vitro gave no evidence of sodium pump inhibition. 5. The erythrocyte sodium pump changed throughout gestation with different components to the change, but, overall, available sodium pump activity in blood increased and sodium content decreased.

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. Exercise-induced pH changes in skeletal muscle were studied in a group of eight subjects with essential hypertension by using 31 P n.m.r. spectroscopy. 2. Leucocyte Na + /H + antiport activity was measured in vitro in the same subjects using a pH-sensitive fluorescent dye. 3. Resting skeletal muscle pH and unstimulated leucocyte pH values were similar to those in control subjects, but increased Na + /H + antiport activity was demonstrated in the leucocytes from hypertensive subjects by acid loading in vitro. Decreased skeletal muscle acidification and an increased rate of pH recovery was also demonstrated in vivo in these same patients during an acid load induced by isotonic exercise. 4. These findings suggest that the increased cellular Na + /H + antiport activity, which has been demonstrated in vitro in essential hypertension, also affects the biochemical response of skeletal muscle to physiological levels of exercise. This strengthens the argument that increased Na + /H + antiport activity in hypertension is a generalized and physiologically relevant cellular abnormality.

1. To determine whether alterations in membrane sodium transport in airway smooth muscle can alter its contractility, we studied the effect of ouabain (a Na + /K + -adenosine triphosphatase inhibitor) and amiloride on contractile responses in bovine trachea and human bronchial rings in a series of studies. 2. Ouabain (10 −6 –10 −4 mol/l) caused concentration-related contraction of bovine trachea with a maximum effect at 30 min; the mean increases in tension with 10 −6 , 10 −5 and 10 −4 mol/l ouabain were 19, 27, and 32%, respectively, of the maximum response seen with 10 −3 mol/l histamine ( n = 6). In human bronchial rings, ouabain (10 −5 mol/l) caused a mean contraction which was 40% of the maximum response to methacholine ( n = 8). 3. Calcium-free fluid (plus ethylenediaminetetra-acetic acid) and nifedipine (10 −5 mol/l) inhibited ouabain-induced contractions, suggesting that contraction was mediated in part by calcium entry via voltage-dependent calcium channels. Phentolamine (10 −5 mol/l) was without effect. 4. Ouabain (10 −5 mol/l) did not alter histamine responsiveness in bovine trachea or methacholine responsiveness in human bronchial rings. 5. Amiloride did not affect resting tone in bovine trachea but caused a concentration-dependent relaxation of bovine tracheal strips preconstricted with carbachol, 10 −3 mol/l amiloride relaxing strips completely over 15 minutes ( n = 8). Pretreatment with amiloride significantly inhibited contraction produced by both histamine and carbachol in a dose-related manner, 10 −5 , 10 −4 and 10 −3 mol/l amiloride shifting the concentration of histamine producing 50% maximal contraction by 3-, 8- and 35-fold ( n = 10) and that of carbachol by 1.4-, 6- and 86-fold ( n = 8), respectively. 6. Amiloride also reduced the contraction produced by 10 −4 mol/l ouabain from 32% (control) to 7% of the maximum histamine response. 7. Our results suggest that alterations in cell membrane sodium transport modify the contractile properties of airway smooth muscle.

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. Using the renal clearance of lithium ( C Li ) as an index of proximal tubular outflow of sodium and water, together with simultaneous measurements of effective renal plasma flow, glomerular filtration rate (GFR) and sodium clearance ( C Na ), renal function and the tubular segmental reabsorption rates of sodium and water during dopamine infusion (3 μg min −1 kg −1 ) were estimated in 12 normal volunteers. 2. C Na increased by 128% ( P <0.001). Effective renal plasma flow and GFR increased by 43% ( P <0.001) and 9% ( P <0.01), respectively. C Li increased in all subjects by, on average, 44% ( P <0.001). Fractional proximal reabsorption [1-( C Li /GFR)] decreased by 13% after dopamine infusion ( P <0.001), and estimated absolute proximal reabsorption rate (GFR– C Li ) decreased by 8% ( P <0.01). Absolute distal sodium reabsorption rate [( C Li – C Na ) × P Na , where P Na is plasma sodium concentration] increased ( P <0.001), and fractional distal sodium reabsorption [( C Li –C Na )/ C Li ] decreased ( P <0.001). 3. It is concluded that natriuresis during low-dose dopamine infusion is caused by an increased outflow of sodium from the proximal tubules that is not fully compensated for in the distal tubules.

1. Amino acids have been used to test renal reserve filtration capacity. Previous studies suggest that amino acids increase glomerular filtration rate (GFR) by reducing distal tubular flow and tubuloglomerular feedback activity. 2. Glomerular function and the renal tubular handling of sodium during infusion of amino acids was studied in 12 normal volunteers. 3. Clearance of sodium ( C Na ) was unchanged. Effective renal plasma flow increased slightly, but significantly, by 9% ( P <0.05). GFR was increased by 13% ( P <0.001). Clearance of lithium ( C Li ) (used as an index of proximal tubular outflow) increased by 38% ( P <0.001). Calculated absolute proximal reabsorption (GFR- C Li ) remained unchanged. Fractional proximal reabsorption [1-( C Li /GFR)] was decreased by 10% ( P <0.001). Calculated absolute distal sodium reabsorption [( C Li – C Na ) × P Na , where P Na is plasma sodium concentration] increased by 40% ( P <0.001). Plasma renin concentration did not change significantly. 4. The results suggest that amino acids increase GFR by a primary effect on renal haemodynamics or, less likely, by reducing the signal to the tubuloglomerular feedback mechanism. The increase in proximal tubular outflow was compensated for in the distal tubules, so that the sodium excretion rate remained unchanged.

1. We measured urinary excretion rates of dopamine (3,4-dihydroxyphenethylamine) and dopa (3,4-dihydroxyphenylalanine) and the spillover rate of dopa into arterial blood during dietary salt loading in conscious Dahl salt-sensitive and salt-resistant rats with intact or denervated kidneys. 2. Dopa spillover was calculated from the steady-state clearance of intravenously infused l -[ 3 H]dopa and arterial levels of endogenous dopa. 3. Daily excretion rates of dopa and dopamine increased by about sixfold during salt loading in both rat strains. Bilateral renal denervation delayed these increases and the natriuretic responses. 4. During dietary salt loading, dopa spillover increased to approximately the same extent as simultaneously measured dopamine excretion. 5. The results suggest that increases in urinary excretion of dopamine during dietary salt loading can be accounted for by increases in the release of dopa into the bloodstream and that the renal nerves contribute to the dopa and dopamine excretory responses.

1. Low intracellular concentrations of myo -inositol in diabetic cells may contribute to the development of tissue damage. The cause of these low levels is unknown, but inhibition of a putative myo -inositol transporter by high concentrations of glucose has been proposed. We have developed a triple-isotope method for estimating myo -inositol influx into human leucocytes and so investigated both the kinetics of this uptake in normal volunteers and the effect of glucose upon it. 2. Uptake was composed of a passive component with a rate constant of 2.4 ± 0.3 × 10 −2 min −1 and a saturable component with a K m of 61 ± 23 μmol/l and a V max. of 11.3 ± 4.5 × 10 −4 mmol min −1 l −1 . Ouabain and low extracellular concentrations of sodium partly inhibited influx. Uptake was predominantly into the cytosolic fraction of the cell with 12% entering the membrane-associated fraction at both 5 and 10 min. 3. myo -inositol influx was significantly inhibited by both d - and l -glucose but not by sucrose. Neither cytochalasin B nor ethyl isopropyl amiloride significantly inhibited uptake. 4. It is concluded that a myo -inositol transporter exists in human leucocytes which is similar to that found in other species and tissues. Our technique allows myo inositol influx in diabetic subjects to be related to varying glycaemic control and tissue damage.

1. Although ethanol appears to alter cellular sodium transport, the exact nature of its effects has not been clearly defined. We have studied the effects of different concentrations of ethanol on human leucocyte sodium content, and on the rise in leucocyte sodium content which occurs during sodium pump blockade with ouabain. 2. Sodium content was significantly reduced after a 20 min incubation with ethanol at concentrations between 17 and 170 mmol/l. 3. The rise in sodium content during a 20 min incubation with ouabain was significantly less in the presence of 170 mmol/l ethanol as compared with 17 mmol/l ethanol. 4. These results suggest that the effect of ethanol on intracellular sodium content is independent of sodium pump activity, i.e. it is mediated through reduced sodium influx.

1. A modified method is described for holding the intracellular pH of leucocytes at different values for prolonged periods of time. 2. Using ammonium sulphate at a final concentration of 8 mmol/l, the buffering power of leucocytes was measured at different internal pH values. 3. A marked dependence of buffering power on internal pH was found. As internal pH was lowered below 7.0, buffering power rose steeply. Above this value, buffering power remained approximately constant. This property may be one factor preventing intracellular acidosis under stress. 4. This method is also suitable for the study of Na + /H + antiport activity. The addition of external Na + to cells acid-loaded to an internal pH of 6.7 led to an ethyl isopropyl amiloride-sensitive 1:1 stoichiometric exchange of external Na + for internal H + .

1. Previous published measurements of leucocyte cation content are inconsistent, with sodium concentrations having particularly high coefficients of variation. We have measured the effects of recovery time after isolation, different types of handling, and centrifugation on leucocyte sodium and potassium content. 2. Sodium content fell markedly during the first 30 min after isolation and was stable from 1 to 3 h of incubation. There was a small but significant rise in potassium content over the same time period. 3. During incubation, occasional gentle resuspension of the cells gave optimal sodium contents, whereas mixing by inversion caused large falls in sodium and potassium content. 4. Centrifugation of stable cells at 200 g for 6 min caused marked increases in sodium content.

1. The synthesis of prostaglandin (PG) E 2 , PGF 2α , 6-keto-PGF 1α and thromboxane (TX) B 2 by isolated glomeruli, cortical tubules, inner medullary slices and outer medullary slices was measured in salt-depleted (LNa) rats and in salt-depleted rats receiving captopril (LNa-CEI). Animals were studied before and after 4, 9 and 15 days of Na + depletion. 2. Na + balance was reached in LNa rats after 4 days. Blood pressure and creatinine clearance remained stable. Serum Na + decreased from 140 ± 1 to 126 ± 1 mmol/l (mean ± sem , P < 0.01). In contrast, LNa-CEI rats were unable to conserve Na + adequately: fractional excretion of Na + and natriuresis were constantly greater than in LNa animals. As a consequence, LNa-CEI rats developed severe hyponatremia, lost weight and their creatinine clearance decreased. 3. The glomerular synthesis of PGE 2 , PGF 2α and 6-keto-PGF 1α , but not of TXB 2 , was significantly increased in LNa rats. In LNa-CEI rats, the synthesis of PGE 2 and 6-keto-PGF 1α was similar to control values, but PGF 2α and TXB 2 synthesis was elevated at day 9. In cortical tubules, PGE 2 and PGF 2α were unaffected by Na + depletion, but 6-keto-PGF 1α and TXB 2 were increased and a similar trend was observed in LNa-CEI rats. In outer medulla of LNa rats, a decrease in all the eicosanoids measured was observed at day 4. In LNa-CEI animals, the synthesis of PGE 2 and PGF 2α , but not of 6-keto-PGF 1α and TXB 2 , was significantly depressed. In inner medulla, Na + depletion only tended to decrease PGF 2α and 6-keto-PGF 1α , but in the presence of captopril, the synthesis of all prostanoids was significantly decreased.

1. Erythrocyte Na + transport (Na + pump activity, co-transport, countertransport and passive Na + efflux) and intracellular Na + concentration were studied in 10 normal individuals and in 29 uraemic patients on chronic haemodialysis, before and after a haemodialysis session. Eight of them fulfilled the criteria of hypertension. 2. Normotensive patients before haemodialysis were classified in two groups: group 1 (pump –) with decreased erythrocyte Na + pump activity, and group 2 (normal pump) with normal erythrocyte Na + pump activity. Group 1 showed, compared with controls, a normal intracellular Na + concentration and a decreased co-transport, but no difference in either countertransport or passive Na + efflux. After haemodialysis this difference disappeared. Before haemodialysis, group 2 showed a high intracellular Na + concentration, but activities of the Na + transport systems studied were similar to those of controls. After haemodialysis, cell Na + concentration decreased to a level not significantly different from that of controls. 3. Both before and after haemodialysis, hypertensive patients showed Na + transport system activities and an intracellular Na + concentration similar to those of controls. 4. Endogenous digoxin-like immunoreactivity (EDLI) and erythrocyte Na + transport were studied in five normotensive and five hypertensive patients, before and after haemodialysis. EDLI in plasma was similar in both groups before and after haemodialysis. No correlation was found between EDLI and erythrocyte Na + pump activity. 5. These results suggest the existence in some dialysed uraemic patients of alterations in erythrocyte Na + fluxes, which may be corrected by haemodialysis. EDLI and erythrocyte Na + fluxes do not seem to be markers of secondary hypertension in these patients.

1. One hundred and five primigravidae were followed sequentially at 4-weekly intervals starting at gestational week 31. They were seen again at 6 weeks post partum . 2. At each visit measurements were made of blood pressure as well as of leucocyte and erythrocyte sodium and potassium content. 3. Eighty-five subjects completed the study. Seven developed pre-eclampsia. 4. In both controls and patients who developed preeclampsia, leucocyte and erythrocyte sodium content increased with gestational age and fell post partum . These changes were of greater magnitude in the patients with pre-eclampsia. Cell potassium fell in both groups, but to a greater extent in patients with pre-eclampsia. 5. These changes in cell sodium paralleled those in blood pressure in both groups. 6. These data suggest that the excessive blood pressure changes in pre-eclampsia might be related to similar changes in cell sodium content.

1. Leucocyte Na + influx in media containing 10 mmol/l Na + was studied directly using a triple-isotope method for measuring initial 22 Na uptake rates in 20 normal and 18 untreated hypertensive subjects. The effects of 1 mmol/l amiloride (a Na + -H + -antiport inhibitor) and 0.1 mmol/l bumetanide (a Na + , K + , Cl − -symport inhibitor) were also examined. 2. The total, amiloride-sensitive and bumetanide-sensitive influx rates were raised in hypertensive compared with normotensive subjects [median (range): total 0.63 (0.25–1.82) vs 0.40 (0.09–0.65) mmol min −1 l −1 , P < 0.002; amiloride-sensitive 0.43 (0.18–1.56) vs 0.26 (0.04–0.48) mmol min −1 l −1 , P < 0.002; bumetanide-sensitive 0.12 (−0.03 to 0.83) vs 0.02 (−0.25 to 0.21) mmol min −1 l −1 , P < 0.005]. 3. We conclude that hypertensive patients have a raised leucocyte total Na + influx when measured in media containing 10 mmol/l Na + and that this is contributed mainly by amiloride-sensitive and bumetanide-sensitive Na + influx mechanisms.

1. The effects of the infusion of a low dose (2 pmol min −1 kg −1 for 3 h) of human atrial natriuretic peptide (hANP) were studied in seven healthy volunteers undergoing a water diuresis. Lithium clearance was used to monitor proximal tubular function. 2. hANP increased urine flow rate, sodium, calcium and magnesium excretion without significant changes in potassium and phosphate excretion, heart rate or blood pressure. 3. hANP caused a small change in fractional lithium clearance, and larger changes in distal nephron handling of sodium and water. 4. Plasma renin activity tended to decrease during the infusion of hANP, while plasma aldosterone concentration decreased during and increased after stopping the infusion of hANP. 5. The data suggest that hANP inhibits the reabsorption of sodium and water by an action on distal segments of the nephron and perhaps the proximal tubule. Inhibition of renin and aldosterone secretion may contribute to the natriuresis.