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1. Plasma sodium concentration may influence renal sodium excretion. We have examined the possibility that the fall in plasma sodium that occurs during salt restriction in man might be an important stimulus for renal sodium conservation. 2. In order to prevent the fall in plasma sodium that usually occurs during dietary salt restriction, we water restricted (200 ml/day) six normal subjects for the 2 days after the transition from 260 (high-sodium diet, day 3) to 20 mmol (low-sodium diet, days 4 and 5) sodium per day. In the control (hydrated) group water intake was held constant at 1800 ml/day. 3. Plasma sodium fell during the low-sodium diet in the hydrated group but remained constant in the dehydrated group (141.3 ± 0.2 to 140.2 ± 0.2 mmol/l versus 141.1 ± 0.3 to 141.3 ± 0.3 mmol/l). Plasma arginine vasopressin concentration was significantly higher and urine flow lower during the low-sodium diet in the dehydrated group (arginine vasopressin on day 5: hydrated group, 0.72 ± 0.1 pmol/l; dehydrated group, 2.18 ± 0.5 pmol/l). Weight fell by a similar amount in both groups (hydrated group, 1.23 ± 0.17 kg; dehydrated group, 1.45 ± 0.19 kg). 4. On the low-sodium diet there were no differences between groups in changes in plasma renin activity (hydrated group, 1.6 ± 0.24 to 4.78 ± 0.65 nmol angiotensin I h−1 ml−1; dehydrated group 1.57 ± 0.18 to 5.14 ± 0.56 nmol angiotensin I h−1 ml−1) or atrial natriuretic peptide (hydrated group, 23 ± 2.3 to 14.7 ± 1.6 pg/ml; dehydrated group, 26.8 ± 3.6 to 12.7 ± 1.3 pg/ml). Salivary aldosterone concentration increased further in the dehydrated study, but only on day 5. 5. Sodium excretion fell further in the dehydrated group over the first 16 h of the low-sodium diet on day 4 (hydrated group, 8.62 ± 0.76 mmol/h; dehydrated group, 6.57 ± 0.38 mmol/h). Creatinine clearance fell on day 5 (low sodium) in the dehydrated group but did not change significantly in the hydrated group (hydrated group, 152 ± 7 to 137 ± 7; dehydrated group, 157 ± 7 to 123 ± 7 ml/min). 6. We conclude that the fall in plasma sodium during salt restriction is not an important trigger for renal sodium conservation in man. The principal difference between studies was the elevation of arginine vasopressin in the dehydrated study. Differences in salivary aldosterone concentration occurred on day 5 only, too late to account for the differences in sodium excretion on day 4. Under the conditions of this study, our findings could be explained if physiological range elevation of arginine vasopressin has an antinatriuretic effect.

1. We have studied the response of six patients with cranial diabetes insipidus and six age-matched control subjects to dietary sodium restriction during constant administration of the synthetic vasopressin analogue desamino-[8-D-arginine]vasopressin. 2. Urine flow increased on the first low salt day in the normal control subjects but not in the patients with cranial diabetes insipidus. Body weight fell 1.35 kg in the control subjects but was constant in the patients with cranial diabetes insipidus. 3. Urinary sodium excretion fell at the same rate in both groups. Diurnal variation of urinary sodium excretion and creatinine clearance was present in the control subjects but not in the patients with cranial diabetes insipidus. 4. Changes in plasma sodium concentration and osmolality were similar. Plasma protein concentration increased more in the control subjects (from 69.1 + 13 to 73 + 1.2 versus from 71.7 + 1 to 73.2 + 1.1 g/l). The responses of plasma atrial natriuretic peptide, plasma renin activity and salivary aldosterone concentration were similar between the two groups. Salivary aldosterone concentration levels were consistently higher in the patients with cranial diabetes insipidus. 5. We confirm that the low salt diuresis is triggered by release from the antidiuretic activity of arginine vasopressin. In the patients with cranial diabetes insipidus extracellular fluid osmoregulation appeared to be achieved by the movement of water out of and sodium into the extracellular fluid. 6. Absent posterior pituitary function and hypothalamic disturbances did not alter renal sodium conservation. Total extracellular fluid sodium appeared to be lower in the patients with cranial diabetes insipidus than in the control subjects. Disturbances of hypothalamic and pituitary function may have caused resetting of overall sodium balance and altered diurnal cycles of urinary sodium excretion and creatinine clearance.

1. The effects of change from a high to low sodium diet upon renal sodium and water excretion and hormone responses were studied in patients with dissociated sympathetic control (DS, tetraplegic) and controls with sympathetic control largely intact (IS, paraplegic). 2. Total and fractional urinary sodium excretion fell in response to sodium restriction in both groups, but the fall in fractional sodium excretion was greater in the DS group compared with the IS group (DS, 1.34 +/- 0.12 to 0.42 +/- 0.05%; IS, 0.96 +/- 0.08 to 0.52 +/- 0.06%). 3. Supine mean arterial pressure fell during the low salt period in the DS group (80.2 +/- 2.7 to 74.4 +/- 2.3 mmHg) but was unaffected by salt restriction in the IS group (101 +/- 2.3 to 98.8 +/- 2.7 mmHg). In the DS group, creatinine clearance remained constant throughout the low salt period (103.7 +/- 7.9 to 98.3 +/- 9.7 ml min-1), but fell during salt restriction in the IS group (101.4 +/- 8.5 to 83.2 +/- 5 ml min-1). 4. Plasma renin activity was lower during salt loading in DS subjects but increased more rapidly and to higher levels in response to salt restriction (DS, 1021 +/- 142 to 4439 +/- 355; IS, 1765 +/- 269 to 3683 +/- 465 pg angiotensin I ml-1 h-1). Plasma atrial natriuretic peptide concentration was higher in the DS group during salt loading and salt restriction (DS, 37.6 +/- 5.6 to 22 +/- 3.8; IS, 20.2 +/- 2.3 to 11 +/- 1.6 pg ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Patients with ileostomies show an early diuresis when sodium restricted; this, together with an obligatory ileal sodium loss, predisposes them to severe salt and water depletion. The role of arginine vasopressin in this circumstance and whether it is natriuretic, or antinatriuretic, is unclear. There is also controversy over its likely effect on small bowel fluid reabsorption. We have examined the effect of the non-pressor (V2) synthetic vasopressin analogue 1-deamino-8-D-arginine (desmopressin) on renal and ileal sodium and water excretion in ileostomy patients during acute adaptation to a low sodium diet. Patients were studied on two separate occasions (nonrandomised) with and without the administration of desmopressin (0.75 micrograms intramuscular, three times a day). In eight subjects without desmopressin there was pronounced diuresis on the first low sodium day, associated with a fall in renal sodium excretion and no change in ileal output or composition. In five (of the original) subjects with desmopressin there was pronounced antidiuresis, no change in renal sodium excretion, and no change in ileal output or composition. In both studies rises in plasma renin activity and salivary aldosterone concentration lagged behind the early decline in renal sodium excretion. We have confirmed the phenomenon of 'low sodium' diuresis after sodium restriction in ileostomy patients and shown that it can be prevented by desmopressin. Desmopressin has no direct or indirect effect on renal sodium excretion or ileal fluid and electrolyte loss in humans.

1. We have previously described a progressive antidiuresis in response to low-dose vasopressin infusion during salt restriction in man, despite stable or even declining plasma vasopressin concentration. In the present study we examine the hypothesis that renal sensitivity to the antidiuretic effect of arginine vasopressin may be enhanced by salt restriction. 2. Extremely low-dose infusions of arginine vasopressin were given to normal subjects after equilibration to high (260 mmol/day) and low (20 mmol/day) sodium intakes. 3. Salt restriction increased the antidiuretic effect of arginine vasopressin (2 fmol min−1 kg−1 arginine vasopressin increased urine osmolality from 67.8 ± 2.6 to 196.3 ± 35.7 mosmol/l in the high-salt study and from 268.3 ± 49 mosmol/l in the low-salt study; P < 0.05 between sodium intakes). Glomerular filtration rate, estimated from inulin clearance, was unchanged during arginine vasopressin infusion irrespective of salt intake (high salt 116.5 ± 9.4 to 118.9 ± 6.4 ml/min; low salt, 135.1 ± 9.2 to 111.2 ± 12.4 ml/min). Renal plasma flow, estimated from para-aminohippurate clearance, fell further during infusion of 2 fmol min−1 kg−1 arginine vasopressin in the low-salt study than in the high-salt study (low salt, from 555.7 ± 22.7 to 298.3 ± 27.6 ml/min; high salt, from 544.5 ± 30.2 to 452.9 ± 28.9 ml/min; P < 0.05 between sodium intakes). 4. Plasma atrial natriuretic peptide concentration increased during infusion of 2 fmol min−1 kg−1 arginine vasopressin in the low-salt study (to 136.5% ± 19.9% of baseline, P < 0.05), if anything falling in the high-salt study (to 90.5% ± 13.6% of baseline). Packed cell volume fell during arginine vasopressin infusion in the low-salt study (high salt, to 98.2% ± 0.4% of baseline; low salt, to 95.7% ± 0.4% of baseline, P < 0.05 for the low-salt study only). 5. Plasma arginine vasopressin concentration was constant throughout each study (high salt 0.48 ± 0.12 to 0.48 ± 0.1 pmol/l; low salt, 0.38 ± 0.05 to 0.4 ± 0.04 pmol/l). 6. Our findings suggest that renal sensitivity to the hydro-osmotic and vascular effects of arginine vasopressin is enhanced by salt restriction.

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 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.

We have investigated the haemodynamic and hormonal responses to angiotensin converting enzyme inhibition in 12 patients with primary autonomic failure (AF, 5 pure autonomic failure, 7 multiple system atrophy) and 7 normal subjects. Measurements of blood pressure (BP), heart rate (HR), stroke distance (SO) and cardiac index (CI, continuous wave Doppler, forearm blood flow (FBF, strain gauge plethysmography) and digital skin blood flow (DSBF, laser Doppler flowmetry) were made non-invasively. Plasma renin activity (PRA) and noradrenaline (NGRAD) were measured before and at 30 min intervals after captopril (50 mg, oral). Basal supine BP was higher in AF compared to normals (p l 0.05). After captopril, mean BP fell in AF (117 ± 6 to 103 ± 5 mmHg, p l 0.05). but not in normals (99 ± 4 to 97 ± 5 mmHg, ns). HR was unchanged after captopril in both groups. The depressor response in AF was accompanied by a fall in SD (9.6 ± 1.2 to 7.6 ± 0.7 cm, p l 0.05) and in CI (676 ± 79 to 536 ± 65 cm/min, p l 0.05). SD and CI were unchanged after captopril in normals (SD, 7.7 ± 1.3 to 7.4 ± 0.6 cm; CI. 579 ± 117 to 571 ± 69 cm/min, both ns). There was no reduction in forearm or digital skin vascular resistance after captopril in either group. Basal PRA in AF was similar to normals, but did not rise after captopril (691 ± 217 to 681 ± 221 pg/ml/hr, ns), unlike normals (813 ± 103 to 1360 ± 290 pg/ml/hr, p l 0.05). NORAO was unchanged after captopril in both groups. We conclude that. captopril lowers blood pressure in AF, unlike normals. The depressor response in AF occurs independently of plasma renin levels and sympathetic nervous activity, suggesting that alternative mechanisms, including accumulation of bradykinin and prostaglandins, may be responsible.

I first met George Pickering when I was a medical student in the Anatomy Department at St Mary's Hospital Medical School. He brought an amputated leg which had arteriovenous anastomoses within it, leading to overgrowth of the limb and subsequently to amputation to try and correct the high cardiac output and failure which it caused. He had injected the arteries with a barium paste and wanted someone to try and find the connections by simple dissection. As I liked dissection, I volunteered, and though I was unable to show any major connections, which were presumably at arteriolar-venular level, it was to mark the beginning of a very long apprenticeship.

1. The cardiovascular and hormonal effects of intravenous saralasin (0.5, 1 and 5 μg min−1 kg−1) were assessed in nine tetraplegic patients (with complete cervical spinal cord transaction above the sympathetic outflow) and in six normal subjects. 2. In the tetraplegic patients, saralasin caused an immediate transient pressor response which was not dose-dependent and substantially greater than the pressor response in normal subjects. The pressor response in the tetraplegic patients was not accompanied by a rise in levels of plasma noradrenaline. 3. In the tetraplegic patients, after α-adrenoceptor blockade with thymoxamine (1 mg kg−1 h−1), twice the dose of intravenous noradrenaline was needed to induce the same pressor response. The pressor response to saralasin (5 μg kg−1 min−1), however, was unaffected by thymoxamine. 4. Saralasin caused minimal changes in levels of plasma renin activity and plasma aldosterone in both groups. There was no relationship between basal plasma renin activity and the pressor response in either group. 5. We therefore conclude that the immediate transient pressor response to saralasin in man is not due to central sympathetic stimulation, is unlikely to be due to peripheral sympathetic activation and is probably the result of intrinsic angiotensin II-like myotropism.

SUMMARY 1. The effect of intravenous vasoactive intestinal peptide (VIP, 6 pmol/kg per min) on renal function in six patients with cirrhosis of the liver was examined. 2. VIP caused generalized vasodilation and increased plasma renin activity, but diminished the glomerular filtration rate by about one third. 3. The excretion of water, sodium, potassium and calcium also fell significantly. 4. These results differ from our findings in normal man in whom VIP diminished water and electrolyte secretion largely by increasing tubular reabsorption. 5. It is concluded that the elevated VIP levels present in patients with severe liver disease may affect renal function, but that the presence of liver disease may affect renal responses to VIP.

115 factory workers (62 white, 53 black) were studied with measurements of blood pressure, plasma noradrenaline concentration, and plasma renin activity. Blood pressure was higher in blacks than in whites. There were no ethnic differences in plasma noradrenaline, which increased with age, but was not related to blood pressure. Mean plasma renin activity was 55% lower in blacks than whites and this difference was not related to differences in sodium intake. There were no associations between renin and noradrenaline, or between renin and blood pressure.

1. The effect of endogenous sympathetic stimulation (induced by urinary bladder stimulation) and intravenous infusion of noradrenaline and isoprenaline on blood pressure, heart rate and levels of plasma renin activity and plasma aldosterone were studied in six tetraplegic patients. Data from infusion studies were compared with data from six normal subjects studied in an identical manner. 2. Bladder stimulation in the tetraplegic patients caused a marked rise in blood pressure and fall in heart rate, but no change in plasma renin activity or plasma aldosterone. 3. Noradrenaline infusion resulted in an enhanced pressor response in the tetraplegic patients when compared with the normal subjects. Heart rate fell in both groups. Plasma renin activity and plasma aldosterone did not change in either group. 4. Isoprenaline infusion caused a fall in both systolic and diastolic blood pressure in the tetraplegic patients, unlike the normal subjects in whom there was a rise in systolic and a fall in diastolic blood pressure. Heart rate and plasma renin activity rose in both groups. Plasma aldosterone did not change in either group. 5. We conclude that in tetraplegic patients neither endogenous sympathetic stimulation by bladder stimulation nor infusion of noradrenaline raises plasma renin activity. Isoprenaline increases plasma renin activity to the same extent as in normal subjects. Renin release mechanisms in tetraplegic patients therefore do not appear to be hypersensitive to catecholamines. Plasma aldosterone is not influenced by any of the stimuli.

1. The influence of cyclic adenosine 3',5'-monophosphate (cyclic AMP), cylic guanosine 3',5'-monophosphate (cyclic GMP) and theophylline on renin secretion was examined in the isolated kidney of the rat perfused with Krebs dextran solution. 2. Neither cyclic AMP (10(-6) to 10(-4) M) nor dibytyryl cyclic AMP (10(-5) M) produced an increase in renin secretion. 3. Cyclic GMP and 8 Br-cyclic GMP caused a small rise in renin secretion in some experiments but this effect was independent of the dose and its physiological significance is uncertain. 4. Theophylline (10(-6) to 10(14) M) caused a significant elevation in renin secretion which was not blocked by (+)-propranolol. Theophylline with cyclic AMP or cyclic GMP did not produce an amplified effect. 5. Despite previous suggestions that cyclic AMP stimulated renin secretion, this could not be confirmed in the present preparation. Since there is no evidence that cyclic AMP or cyclic GMP (or their derivatives, dibutyryl cyclic AMP and 8 Br-cyclic GMP) enter the cells, it will be necessary to study their activity in isolated juxtaglomerular cells to define a possible role.

1. A renin-inhibitory material has been partially purified from soluble extracts of the pig kidney cortex by ammonium sulphate precipitation and diethylaminoethylcellulose (DEAE) chromatography and its properties studied. 2. It displayed competitive type kinetics. It did not inhibit cathepsin D, carboxypeptidase A, pancreatic kallikrein or trypsin. 3. Renins from dog, rabbit and rat were inhibited, but not those from sheep or man, when assayed with pig angiotensinogen. 4. The material was inactivated by treatment with trypsin, N-ethylmaleimide or p-chloromercuribenzoate. 5. Renin-inhibitory activity was not found in plasma from peripheral blood of pigs. 6. It is concluded that the function of the renin inhibitor in the renal cortex of the pig may be restricted to the intrarenal environment.

1. The aim of this study was to test whether a postulated gastrointestinal or portal monitor of sodium intake plays any part in adjusting renal sodium excretion when dietary sodium is reduced. 2. Normal male subjects were given 50 mmol of sodium chloride intravenously three times daily for 3 days to replace or to supplement a constant oral intake of sodium chloride. 3. When oral sodium chloride was replaced with intravenous sodium chloride, renal sodium excretion remained constant. 4. When oral sodium chloride was kept constant, sodium administered as intravenous sodium chloride was promptly excreted in three out of four subjects. There was a delay in the increase in sodium excretion in the fourth subject. 5. Infusions containing 50 mmol of sodium chloride in 50 ml given intravenously over 22 min produced a rise in plasma sodium concentration and a fall in concentration of total plasma solids. 6. These results provide no evidence for a gastrointestinal or portal monitor of sodium intake, but do not disprove the existence of such a monitor.

The peptide hormone neurotensin (NT) is found mainly in gut endocrine cells of the ileum, but has also been identified as a putative neurotransmitter in the central and peripheral nervous systems. It may have a dual role as a circulating gastrointestinal hormone and peripheral neurotransmitter. Its predominant effects are to reduce oesophageal sphincter tone, inhibit gastric secretion and emptying and inhibit intestinal motility, but stimulate intestinal and pancreatic exocrine secretion; NT-like immunoreactivity has been found in kidney and therefore NT may influence renal function. When infused i.v. in rabbits it causes antinatriuresis. We have studied its renal effects in 11 healthy males by i.v. infusion under conditions of altered dietary sodium. Postprandial circulating neurotensin levels were reproduced by infusion. There were no consistent systemic or renal haemodynamic effects. Plasma electrolytes and renin did not change. Only renal chloride excretion changed significantly, falling by ca. 30%, and recovering after infusion. There is no evidence for a specific renal tubular chloride transport mechanism, but coupled cotransport, Na+:K+:2Cl−, may be hormonally regulated. NT might stimulate this process and contribute to the renal response to changes in dietary composition, especially sodium intake.

1. The effect of the intravenous administration of aldosterone on the colonic potential difference has been studied in eight normal young males and compared with effects on renal function. 2. Under control conditions the colonic potential was remarkably stable over a period of 10 h of recumbency whereas with infusions of aldosterone ranging from 5·6 to 89·6 pmol min−1 kg−1 (2 to 32 ng min−1 kg−1), the colonic potential difference increased in a quantitatively reproducible fashion. The correlation between change in plasma aldosterone and in colonic potential was highly significant. 3. The delay between the end of the infusion and the maximum change in colonic potential was 4 h. The shortest latent period before any change in colonic potential occurred was 70 min after the start at infusion rates of 11·2 pmol min−1 kg−1 or more. The effect, although still present at 10 h, had returned to control values at 20 h after the start. 4. The main renal effect of aldosterone was on sodium excretion, which was reduced at infusion rates of 11·2 pmol min−1 kg−1 and more, but the relation to dose of aldosterone was not very quantitative and the effect was more like a threshold response. 5. The conclusion is that the colonic potential difference may be used as a quantitative indicator of the actions of aldosterone and is more sensitive and dose-dependent than the renal effects.

We studied the haemodynamic effects of clonidine (2 micrograms/kg/iv) in 7 tetraplegics and 7 normal subjects. Measurements of blood pressure, stroke volume, cardiac output and digital (finger) skin blood flow were made before and after clonidine for 60 minutes. Blood pressure, stroke volume and cardiac output did not fall in tetraplegics, unlike normals. Resting digital skin blood flow was higher in tetraplegics and fell after clonidine. In normal subjects however, an increase in digital skin blood flow occurred after clonidine. The pressor and digital vasoconstrictor responses to bladder stimulation were attenuated after clonidine. The inability of clonidine to induce a fall in blood pressure, stroke volume, cardiac output and cause peripheral vasodilation in tetraplegics is consistent with its central sympatholytic effects. Attenuation of the responses to bladder stimulation suggest an effect on spinal sympathetic neurones.

1. The electrolyte and water composition of urine and ileal fluid was studied in six patients with ileostomies during dietary sodium deprivation and at the same time measurements were made of plasma renin activity, plasma aldosterone concentration, renal aldosterone excretion and plasma arginine vasopressin concentration. 2. In each subject there was a reduction in renal sodium excretion within 24 h of sodium deprivation. Significant rises in plasma renin activity, plasma aldosterone concentration and renal aldosterone excretion occurred by day 2 of sodium deprivation. 3. There was only modest conservation of sodium by the ileum during sodium deprivation, but ileal potassium concentration rose progressively. There were significant associations between ileal-fluid potassium concentration and plasma renin activity or renal aldosterone excretion. 4. Under the conditions of the experiment a diuresis was observed in each subject during dietary sodium deprivation. This did not appear to depend on changes in plasma arginine vasopressin concentration.

We have determined the haemodynamic responses to a balanced liquid meal in eight normal subjects, before and after administration of the somatostatin analogue, Octreotide (SMS 201-995), which inhibits the release of gastrointestinal peptides. In the absence of Octreotide ingestion of the meal caused a marked increase in superior mesenteric artery (SMA) blood flow. Blood pressure was maintained, presumably by a compensatory rise in cardiac output and forearm vascular resistance. After Octreotide there was a fall in SMA blood flow alone, with no further changes after food ingestion. We conclude that Octreotide prevents the haemodynamic changes following food ingestion, probably by inhibiting the release of those gastrointestinal peptides that induce splanchnic vasodilatation.

1. The respective role of alpha-adrenergic and beta-adrenergic receptors in mediating the effect of catecholamines on renin secretion was examined in the isolated perfused rat kidney. 2. Noradrenaline, which has combined alpha- and beta-adrenergic activity, stimulated renin secretion only in the presence of the alpha-receptor blocking agent phenoxybenzamine. This stimulatory effect was largely prevented by the addition of the beta-blocking agent, propranolol. The vasoconstrictor action of noradrenaline, and thus the rise in mean renal perfusion pressure, was abolished by phenoxybenzamine. Our previous finding that noradrenaline alone stimulated renin release was inconclusive (Vandongen, Peart & Boyd, 1973). 3. Noradrenaline stimulated renin secretion when calcium was excluded from the perfusion fluid, to which disodium EDTA (25 mmol/l) was added. The vasoconstrictor action of noradrenaline was considerably attenuated under these conditions. 4. Methoxamine, which has only alpha-adrenergic activity, did not increase renin secretion when infused alone or with phenoxybenzamine. The increase in renin secretion after beta-adrenergic stimulation with isoproterenol was significantly suppressed by methoxamine, although this was associated with an increase in mean renal perfusion pressure. 5. These findings indicate the importance of intrarenal beta-adrenergic receptors in the stimulation of renin secretion and suggest that an opposite inhibitory effect on renin secretion follows alpha-adrenergic activity. 6. Although the results do not exclude a direct effect of vascular tone and renal perfusion pressure, it is suggested that the stimulation and inhibition of renin secretion is related to smooth muscle activity by the involvement of a calcium-dependent process similar to that involved in contraction and relaxation. This would accord with the common derivation of the renin-producing and vascular smooth muscle cells

The effects of 300 micrograms of oral clonidine were studied in nine patients with unilateral renal artery stenosis proved by selective renal arteriography. Blood pressure, heart rate, plasma renin activity (PRA) levels, plasma noradrenaline levels, and sedation were measured before and for eight hours after dosage. After clonidine administration, both systolic and diastolic blood pressure fell within the first hour, was maximum in the fourth hour, and remained lower than predosage levels even in the eighth hour. There was a fall in heart rate, maximum in the fourth hour. There were minimal changes in PRA levels after giving the clonidine. Plasma noradrenaline levels fell, with the maximum fall in the sixth hour. Sedation occurred within one hour of dosage and was maximum in the second hour. We conclude that in patients with unilateral renal artery stenosis clonidine causes a substantial and prolonged fall in blood pressure not accompanied by suppression of PRA levels but by a reduction in plasma noradrenaline levels. This suggests a role for central pressor mechanisms, probably linked to angiotensin II and central sympathetic activation, in the maintenance of hypertension in patients with renal artery stenosis.

1 The effect of pindolol administered to twenty-six patients with hypertension of unknown origin was compared with respect to blood pressure and plasma renin activity change after increase of the dose over a period of 6 weeks. 2 There was no clear correlation between the fall of plasma renin activity, which in some patients was very marked, and the fall in blood pressure. Some patients with a fall in plasma renin activity did not drop their pressure. Conversely, some with a fall of pressure did not drop their plasma renin activity. 3 The addition of hydrochlorothiazide to the pindolol finally caused further lowering of the blood pressure in all but one patient and the plasma renin activity rose in all but two patinets. There was no clear correlation between change in plasma renin activity and the effect on blood pressure.

Diurnal studies were performed on ten normal volunteers taking a normal sodium diet. Half-hourly blood samples were taken throughout 25 h and assayed for plasma renin activity (PRA) and the plasma concentrations of noradrenaline, aldosterone and cortisol. Sleep was recorded polygraphically and scored by standard criteria. Circadian rhythms were demonstrated for plasma cortisol, aldosterone and noradrenaline concentrations, but not for plasma renin activity. The nadir of the rhythm for the noradrenaline concentration appeared to be related to sleep itself rather than to any chronological index. Only PRA was effected by the stage of sleep, falling sharply during periods of REM sleep. Plasma cortisol and aldosterone concentrations showed a positive correlation over the 24 h. There was, however, no correlation between PRA and plasma aldosterone concentrations, except when the subjects arose after their night's recumbency. Plasma noradrenaline concentration did not correlate with the concentration of any of the other hormones measured.

Following a random block experimental design in each case, three repeated measurement studies were carried out in three different groups of conscious rabbits, to investigate the renal effects of increasing doses of intravenous calcium chloride (CaCl2) and bovine parathyroid hormone (PTH). In the first study, each rabbit received either CaCl2 (0.15, 0.3, 0.5 or 1.0 mg kg-1 min-1) or vehicle alone (control) for 160 min. In the second study, rabbits were given either PTH (0.15 microgram kg-1 min-1), CaCl2 (1.0 mg kg-1 min-1), PTH plus CaCl2 (0.15 microgram kg-1 min-1 and 1.0 mg kg-1 min-1, respectively) or vehicle alone; PTH was infused for just over 60 min. In the third study, a much smaller dose (0.05 mg kg-1 min-1) of CaCl2 was infused for 100 min. CaCl2 infusion produced a striking fall in fractional excretion of sodium of at least 50% (P less than 0.01), but this was not dose related, being almost maximal at the smaller doses infused. Although this effect was evident in the absence of any changes in total plasma calcium concentration at the lower doses of CaCl2, renal calcium excretion was increased between 2- and 20-fold (P less than 0.01) at all doses infused. Fractional excretion of chloride doubled at the two higher doses of CaCl2 (P less than 0.01), but potassium excretion was unchanged. There were no consistent alterations in mean arterial blood pressure, effective renal plasma flow, glomerular filtration rate or plasma renin activity (PRA); total plasma calcium concentration was consistently elevated only during infusion of the high dose by just under 1 mmol l-1. PTH infusion had no measured effect on fractional excretion of sodium or renal calcium excretion, but doubled fractional potassium excretion (P less than 0.05). Heart rate and PRA increased (P less than 0.01 and less than 0.05, respectively), the latter by 50%, but systemic pressure and renal haemodynamics were not significantly affected. By contrast, PTH infused with CaCl2 produced a 4-fold rise in fractional sodium excretion and although renal calcium excretion remained increased, it was reduced by ca. 80% when compared with renal calcium excretion during infusion of CaCl2 alone. Infusion of PTH alone increased PRA, but when PTH and CaCl2 were infused together, PRA did not change.(ABSTRACT TRUNCATED AT 400 WORDS)

1. The role of the sympathetic nervous system in the release of renin during head-up tilt has been studied in five normal subjects and in four tetraplegic patients with cervical spinal-cord transection above the sympathetic outflow. Blood pressure, heart rate and concentrations of plasma noradrenaline, plasma adrenaline and plasma renin activity were measured during head-up tilt to 45° before and after acute β-adrenoreceptor blockade with intravenous propranolol. 2. In the normal subjects there were minimal changes in blood pressure during head-up tilt and there was a rise in both plasma noradrenaline concentration and plasma renin activity. After propranolol values of plasma renin activity at rest fell with little change occurring during head-up tilt. 3. In the tetraplegic patients there was a substantial fall in blood pressure during head-up tilt. Concentrations of plasma noradrenaline and adrenaline did not change but there was a marked increase in plasma renin activity. Values of plasma renin activity both at rest and during head-up tilt were unaffected by propranolol. 4. We conclude that in tetraplegic patients renin release during head-up tilt may occur independently of sympathetic nervous activity and is probably largely dependent on activation of renal vascular receptors.

1. A group of rabbits was actively immunized against aldosterone and their subsequent response to infused aldosterone and to dietary sodium restriction was compared with that of a control group. 2. Colonic electrical potential difference (CP) was used as an index of relative mineralocorticoid activity in both groups of animals. 3. Infusion of aldosterone produced a rise in CP to a maximum of −50 to −70 mV at rates of infusion of 55–270 pmol min−1 kg−1. In contrast, the immune group showed no change until infusion dose rates of 2700 pmol min−1 kg−1 were used. 4. During dietary sodium restriction, CP increased in normal rabbits to a significantly greater degree than in immune animals although cumulative urinary sodium losses were the same in both groups. 5. The ability of the immune animals to remain in sodium balance despite physiological aldosterone blockade suggests that aldosterone is not an essential component of their sodium-conservation mechanisms.

Pentagastrin and cholecystokinin octapeptide (CCK8) were infused i.v. at three different doses in two sets of 4 conscious rabbits following a repeated measurements design (130, 1,300 and 13,000 pmol kg-1 min-1 pentagastrin; 5, 50 and 450 pmol kg-1 min-1 CCK8). In man, two different doses of pentagastrin (13 and 65 pmol kg-1 min-1) were infused in two groups of 6 subjects, and CCK8 (2 pmol kg-1 min-1) in a third group. According to published human postprandial levels, plasma CCK8-like immunoreactivity concentrations were supraphysiological at all doses infused. In the rabbit, pentagastrin produced a dose-related fall in urine flow and free water clearance, but no significant change in systemic and renal haemodynamics, electrolyte excretion and measured plasma constituents; however, in human subjects, pentagastrin increased renal sodium excretion and reduced potassium excretion but did not change glomerular filtration rate. In the rabbit, CCK8 produced a dose-related fall in plasma renin activity, plasma calcium concentration and mean arterial blood pressure; dose-dependent increases in effective renal plasma flow, glomerular filtration rate and renal sodium excretion. In man, changes in sodium and potassium excretion similar to pentagastrin were observed; there were no significant changes in plasma renin activity, plasma calcium concentration, blood pressure, effective renal plasma flow or glomerular filtration rate. The pharmacological renal effects of pentagastrin in conscious water-loaded rabbits resemble vasopressin. In contrast, CCK8's most striking effect was vasodilatation and was unusual in inhibiting rather than stimulating renin release. In man the net changes in urine composition found during infusion of these peptides are similar to those produced by the potassium-sparing diuretics, amiloride and triamterene. However the generally weak renal effects observed, even at pharmacological doses, indicate that these peptides are unlikely to influence renal function under normal physiological conditions.

1. The effect of single and combined infusions of angiotensin and aldosterone on colonic potential difference, blood pressure and renal function was studied in two normal male subjects and four female patients with adrenal deficiency maintained only on cortisone. 2. Aldosterone had its usual effect on colonic potential difference and it was possible to show that angiotensin had a small but definite effect of its own in the absence of aldosterone. The two hormones produced a summation response when given together. 3. The effects on renal function in two normal young male subjects were similar to those known previously. The response of the patients was different and probably reflected a number of factors, such as age, sex and long-standing adrenal deficiency. 4. Although the numbers were small, both normal subjects and patients showed a significantly greater rise of blood pressure with combined infusions of angiotensin and aldosterone than with angiotensin alone. The plasma concentrations of angiotensin were similar with both types of infusion, and so increased sensitivity to angiotensin in the presence of aldosterone is postulated.

1. The renal excretion of water, electrolytes, aldosterone and kallikrein was monitored in 12 ileostomized patients before and during sodium deprivation. Changes in plasma renin activity (PRA), plasma aldosterone and plasma arginine vasopressin (AVP) concentrations were measured, together with aldosterone in ileal fluid. The pattern of gut peptide release in response to a test meal was also examined to assess whether a circulating gut peptide might be involved in the renal adaptation to sodium restriction, and compared with healthy normal subjects who were under no dietary constraint. 2. In each patient renal sodium excretion fell within 8–12 h of sodium deprivation and was associated with a prompt and significant rise in PRA; much later increases in plasma aldosterone concentration and renal aldosterone excretion occurred, and were established by day 2 of sodium restriction. No consistent change in renal kallikrein excretion was found. 3. Ileal sodium loss was little changed by sodium deprivation, but ileal potassium concentration rose steadily and became significantly correlated with PRA, and to a lesser extent with renal aldosterone excretion. 4. Of the gut peptides measured in plasma, only the insulin profile was altered by sodium deprivation, with an increase in the test meal response; insulin has previously been shown to have a significant antinatriuretic action at physiological concentrations. Plasma levels of pancreatic polypeptide and motilin were increased in ileostomized patients when compared with normal subjects, but were unaffected by the change to a low sodium diet. 5. An early increase in urine flow and water diuresis occurred during sodium deprivation, following a cyclical pattern with peaks each evening. There were no corresponding changes in measured plasma AVP concentration or creatinine clearance. This observation remains unexplained.

The mechanisms of the cardiovascular and renin responses to vasoactive intestinal polypeptide (VIP) are unclear. Rabbit studies suggest that VIP-induced tachycardia is largely beta-adrenoceptor mediated, but that the renin response may be partially prostaglandin-dependent. To examine the relative importance of prostaglandins and reflex sympathetic activation in the haemodynamic and renin responses to VIP infusion in man, we completed two randomised single-blind crossover studies in two groups of six healthy male volunteers (aged 24-35 years). We recorded the effects of indomethacin and propranolol pretreatment on VIP-related changes in heart rate (HR), blood pressure (BP), forearm vascular resistance (FVR), plasma renin activity (PRA), plasma noradrenaline (PNA) and plasma arginine vasopressin (AVP) concentrations. Intravenous VIP (calculated dose: 6 pmol kg-1 min-1) produced cutaneous flushing, increased HR and PRA, decreased FVR, but did not alter mean arterial BP or AVP levels. Indomethacin (375 mg over 3 days) lowered basal PRA and propranolol (circa 40 mg i.v. over 60 min) decreased resting HR and increased FVR. Although indomethacin and propranolol reduced the absolute rise in PRA and HR, respectively, during VIP infusion, the percentage changes were no different from control. Neither drug altered the flush response to VIP and propranolol did not affect the fall in FVR. We conclude that the measured cardiovascular responses to VIP infusion in man are probably direct and do not involve a significant contribution from reflex sympathetic stimulation, nor prostaglandin release.

1. The subcellular distribution of low-molecular-weight and high-molecular weight forms of pig renin has been investigated. 2. Renin, in aqueous extracts of a ‘renin granular fraction’ prepared by differential centrifugation, after gel filtration on Sephadex G-100 displayed an apparent molecular weight of 40 000 and was not activated by acidification to pH 2.8. 3. Renin in the soluble fraction separated on Sephadex G-100 at neutral pH displayed a main peak of activity with an apparent molecular weight of 40000. When eluates were acidified to pH 2.8 (2°C, 60 min) a marked increase in renin activity was observed in the region corresponding to an apparent molecular weight of 50 000. 4. A renin inhibitory material was isolated from the soluble fraction by DEAE chromatography. This material displayed an apparent molecular weight of 50000 and it was destroyed by acidification to pH 2.8. 5. The presence of the proteolytic inhibitor N-ethylmaleimide yielded an apparently high-molecular-weight form of renin (60000–70000) from the soluble fraction, but this was not found in the granular fraction. 6. We conclude that pig renal renin is stored within membrane-bounded subcellular organelles as the low-molecular-weight form. High-molecular-weight renin and renin inhibitory activity are localized to the cortical soluble fraction. In addition, the soluble fraction contains a material which in the presence of N-ethylmaleimide results in the formation of an apparently high-molecular-weight renin.

Conscious rabbits received either vasoactive intestinal polypeptide (VIP) at a dose of 1, 10 or 25 pmol kg-1 min-1 or vehicle alone (control) through an ear vein for 2 h. Experimental design followed a randomized Latin square arrangement. VIP led to a decrease in effective renal plasma flow and glomerular filtration rate (P less than 0.01) during infusion of the middle and high doses. Mean arterial blood pressure rose slightly (P less than 0.05) and filtration fraction increased (P less than 0.01) during infusion of the middle dose. The high dose produced a rise in heart rate, a fall in plasma sodium, potassium and phosphate concentrations and a rise in plasma solids (P less than 0.01). In spite of the renal haemodynamic effects and changes in plasma composition during infusion of the high dose, fractional excretion of sodium, potassium and chloride doubled (P less than 0.05), suggesting a direct action of VIP on renal tubular function. Plasma renin activity increased between 2- and 3-fold (P less than 0.01). The mechanism of the renin response is uncertain. These results, together with the reported presence of VIP-like material in the renal cortex, may indicate a role for VIP in the regulation of renal function, including renin release.

1. The epidemiological characteristics of plasma renin activity (PRA) were established in 1999 members of occupational groups in North and West London. 2. The main finding was that PRA was inversely associated with systolic blood pressure in men, the percentage fall in PRA (on a log scale) being 8.4% for each increase of one standard deviation in systolic blood pressure. There was a less obvious inverse relationship in women. 3. However, blood pressure accounted for less than 1% of the variance in PRA. 4. Mean PRA in both smokers and ex-smokers was about 20% higher than in non-smokers. 5. PRA fell with increasing age, was lower in women than in men and considerably lower in blacks (of either sex) than whites. 6. PRA was lower in the first quarter of the menstrual cycle than in the rest of the cycle. 7. Haemoglobin, blood cholesterol, leucocyte count and Factor VIII were positively correlated with PRA. 8. PRA was lower in men with diagnosed hypertension than in those without; there was no significant difference in the women. 9. PRA was lower in those who had had myocardial infarcts in the past than in those who had not. 10. The data as a whole suggest that it may be low, not high, levels of PRA which are associated with increased risks of cardiovascular disease in which hypertension is a predisposing factor. 11. The explanation may be a homoeostatic fall in PRA in response to a rise in blood pressure rather than a major causal role for PRA in the pathogenesis of essential hypertension and target-organ damage.

1. Dietary sodium reduction in man is followed by rapid conservation of sodium by the kidneys. The rapidity of this response suggests that the gastrointestinal tract is involved in early recognition of changes in sodium intake or in mediation of the compensatory response. 2. In order to test the hypothesis, 100 mmol of sodium was given to normal volunteers in balance on a low-sodium diet (5 mmol/24 h): the dose was given either orally or intravenously. 3. Those who received their sodium orally excreted it more rapidly than those who received it intravenously and the difference was most marked in the first 8 h after the dose. 4. This finding is consistent with the presence of an input receptor for sodium in the gastrointestinal tract.

VIP containing nerves are present in the kidney and plasma VIP levels are elevated in cardiac failure and severe liver disease. We studied the effects of intravenous VIP; 6 pmol kg−1 min−1 on 6 normal subjects and 3 patients with liver disease. In normal subjects VIP produced flushing and significant rises in heart rate and pulse pressure but the clearance rates of paraaminohippurate and creatinine did not change significantly. Urine flow fell to about 1 3 and the rate of excretion of electrolytes (except phosphate) fell to about a half of control values. Plasma renin activity rose about 3-fold and there were significant rises in haematocrit and the plasma concentrations of solids, calcium and phosphate. The patients with liver disease responded similarly. Elevated plasma VIP could contribute to salt and water retention in disease states.

1. A new method of purification of renin is described. This method employs the following procedures: ethanol precipitation; saline extraction; precipitation of renin with 40% ammonium sulphate; precipitation of impurities with 3% ammonium sulphate at pH2·5; chromatography on DEAE-cellulose and CM-Sephadex; gel filtration on Sephadex G-100 (both normal and superfine grade); finally, starch-gel electrophoresis. 2. The final renin preparation had a specific activity 104 times that of the initial saline extract. 3. A single band of stained protein corresponding to the renin activity was present on starch-gel electrophoresis in the final step and a single precipitin line was obtained to this material with rabbit anti-(pig renin) serum. 4. Double diffusion in agar with rabbit anti-(pig renin) serum showed one major precipitin line, probably due to renin–anti-renin complex, and in addition two minor components.

1. The effects of lanthanum on renin release and renal vasoconstriction were studied in the isolated perfused rat kidney. 2. Lanthanum reduced noradrenaline-induced renal vasoconstriction. 3. Lanthanum prevented isoprenaline-induced and glucagon-induced stimulation of renin secretion.