A dynamic study of plasma renin activity and aldosterone concentration in normal and hypertensive subjects

Increased 18-hydroxycorticosterone responses to frusemide in essential hypertension

Plasma concentrations of angiotensin II (AII), aldosterone, 18-hydroxycorticosterone and cortisol were measured in seven patients with benign essential hypertension and in seven age-matched control subjects before, and at frequent intervals for 2 h after the intravenous injection of frusemide (40 mg). In the normal subjects, significant increases in the plasma levels of AII, aldosterone and 18-hydroxycorticosterone were apparent from 15 min after diuretic administration. The integrated responses of each hormone to frusemide administration were calculated. Aldosterone and AII responses to the diuretic were closely related, although three hypertensive patients had normal integrated aldosterone responses despite subnormal increases in the plasma concentrations of AII. The integrated 18-hydroxycorticosterone responses were greater in the hypertensive (median 970 nmol.h h-(1).1-(1)) than in the normal subjects (median 180 nmol.h-(1).1-(1)), P<0.05. Some patients with a raised blood pressure appear to have an enhanced adrenal corticosteroid response to frusemide; this probably reflects an increased sensitivity to angiotensin II.

Increased adrenal sensitivity to angiotensin II in low-renin essential hypertension

Studies were undertaken to determine if the dissociation of aldosterone and plasma renin activity in low-renin essential hypertension is due to altered adrenal responsiveness to angiotensin II. The responsiveness of the adrenal glands to angiotensin II was determined by infusing graded doses of angiotensin II into normal subjects and into patients with essential hypertension and measuring changes in levels of plasma aldosterone in response to the infusion. To minimize the influence of endogenous angiotensin II and ACTH, supplemental sodium and dexamethasone were given before the infusions. Levels of plasma aldosterone and plasma renin activity were determined in normal subjects and in the same patients after the combined stimuli of furosemide and upright posture, a maneuver used to increase the level of endogenous angiotensin II. To determine if the changes in levels of plasma aldosterone during infusion of angiotensin II were due to alteration of the metabolic clearance of aldosterone, the metabolic clearance of aldosterone was measured before and during the infusion of angiotensin II. After sodium loading, dexamethasone treatment, and supine posture, levels of plasma aldosterone of normal subjects and patients with essential hypertension were suppressed equally. In response to the infusion of angiotensin II, the levels of plasma aldosterone of patients with low-renin essential hypertension were significantly higher than those of normal subjects or of patients with normal-renin essential hypertension. After furosemide and upright posture, levels of plasma aldosterone of patients with low-renin essential hypertension were significantly higher than those of patients with normal-renin essential hypertension, despite a blunted response in plasma renin activity of the patients with low-renin essential hypertension. Decreases in metabolic clearance of aldosterone during infusion of angiotensin II were similar in patients with normal-renin essential hypertension and in patients with low-renin essential hypertension and accounted for only a small fraction of the marked increase in levels of plasma aldosterone of patients with low-renin essential hypertension. It is concluded that patients with low-renin essential hypertension have increased adrenal sensitivity to angiotensin II. This increased sensitivity may explain the dissociation of aldosterone and plasma renin activity in low-renin essential hypertension.

Renin and aldosterone response in human newborns to acute change in blood volume

Increased activity of the renin/aldosterone system in the neonatal period is now well established in both animals and man but the control mechanisms are poorly understood. We have monitored the plasma renin activity (PRA) and plasma aldosterone concentration (PAldo) in 14 infants undergoing 21 exchange transfusions. PRA and PAldo were measured before and at 5, 10, 15, 30, 45, and 60 minutes after the injection, and 5, 10, 15, and 30 minutes after the withdrawal of 7 ml blood/kg birthweight immediately before exchange transfusions. PRA increased to a maximum of 53% and decreased to a maximum of 39% of the resting values after withdrawal or injection of blood respectively. PAldo values did not change significantly during the same period. Thus the renin-angiotensin system in the newborn infant is responsive to changes in blood volume.

Furosemide and plasma renin activity in essential hypertension

Changes in arterial blood pressure, renal electrolyte excretion, and plasma renin activity in response to repeated doses of furosemide were measured in 12 patients with essential hypertension admitted to the medical service for electrolyte balance studies. Eighty and 120 mg/day furosemide in divided doses for 5 to 10 days produced a prompt increase in renal sodium excretion. Urinary Na/K concentration ratios, which were elevated during peak natriuresis, returned to control levels following the initial diuretic response. In 2 patients with high initial levels of plasma renin activity, arterial blood pressure was not reduced by furosemide, and more potent antihypertensive agents were required to control the blood pressure. In the remaining patients, furosemide produced a significant decrease in systolic and diastolic blood pressure. There was a general upward shift of plasma renin levels in terms of 24-hour renal sodium excretion in those who demonstrated an antihypertensive response to the drug. However, the average increase in plasma renin activity after repeated doses of furosemide was not statistically significant and no correlation was demonstrated between the level of plasma renin activity after furosemide and the blood pressure lowering effect of the drug.

Enhanced aldosterone response to angiotensin II in human hypertension

Adrenal and vascular responsiveness to graded doses of angiotensin II (A II) were recorded for seven normal subjects and 12 patients with essential hypertension while in balance on an intake of 200 mEq sodium/100 mEq potassium. Patients with essential hypertension had been previously studied and known to have normal responses of plasma renin activity to sodium restriction and upright posture. A II was administered for 30 minutes at rates of 0.1, 0.3, 1, and 3 ng/kg per minute and plasma aldosterone responses were assessed 20 and 30 minutes later; blood pressure was monitored at intervals of 1 minute during infusion of A II at each rate. A significant increment in plasma aldosterone occurred at an infusion rate of 0.3 ng/kg per minute in patients with hypertension. This change was not seen until the infusion rate reached 1.0 ng/kg per minute in the normotensive control subjects. Even at an A II infusion rate of 1 ng/kg per minute, the increment in plasma aldosterone levels in normotensive subjects (4.2 +/- 0.6 ng/dl) was significantly less (P less than 0.001) than that in patients with essential hypertension (19 +/- 3 ng/dl). In both groups, a significant rise in mean arterial blood pressure occurred at an A II dose of 0.3 ng/kg per minute, but the pressor response of the hypertensive group was significantly greater at the highest infusion rate (3 ng/kg per minute) (P less than 0.05). Thus, enhanced adrenal and pressor responsiveness to infused A II was observed in the hypertensive subjects, suggesting a change in A II receptor affinity.

A specific role for saline or the sodium ion in the regulation of renin and aldosterone secretion

It is well established that in normal man the renin-angiotensin-aldosterone system is responsive to changes in volume. The present study was performed to determine whether sodium has an action apart from volume in the regulation of the secretion of renin and aldosterone. Acute volume expansion was induced either by saline, dextran, or glucose infusion in supine, normal subjects in balance on a 10 meq sodium/100 meq potassium diet. Plasma renin activity (PRA), angiotensin II (A II), aldosterone (PA), cortisol, serum sodium, and potassium were measured every 10 min for the first 30 min and then at 1, 2, 4, 6, and 8 h. During saline infusion (500 cm(3)/h for 6 h) mean PRA and A II levels declined very rapidly, falling significantly below control at 10 min (P < 0.01) and by 50% at 60 min. Thereafter, the rate of fall was more gradual, reaching a nadir at 360 min (70-80% below control). PA declined in a parallel pattern except that a significant fall did not occur until 30 min. In contrast to saline, dextran infusion (250 cm(3)/h for 4 h) did not produce a significant fall in PRA, A II, or PA until 4 h after the start of the infusion despite equivalent volume expansion. On the other hand, the infusion of 5% glucose and water (500 cm(3)/h for 6 h) did not produce a significant decline in PRA, A II, or PA over the first 6 h of the study. Although the response rate of PRA, A II, and PA was different in each of the three infusion studies, these parameters were significantly correlated within each study. Serum sodium and potassium levels did not change during any study except dextran infusion, where a significant fall in both occurred at 120 min. In all the infusion studies, plasma cortisol levels gradually declined during the 8-h study period consistent with its expected rhythm of diurnal secretion. These results demonstrate that rate of response of the renin-angiotensin-aldosterone system to acute volume expansion with saline differed from that with dextran and glucose infusion in sodium-depleted man. The data support a specific role for volume expansion with saline or the sodium ion per se in the regulation of renin and aldosterone.