The regulation of aldosterone secretion in anephric man

Progestogen-only pill associates with false-positive aldosterone/renin ratio screening test

Aldosterone/renin ratio (ARR) is commonly used to screen for primary hyperaldosteronism (Conn's disease). A number of drugs can alter ARR measurements, thus requiring omission before testing. However, hormonal agents such as the combined oral contraceptive (COCP) or progestogen-only pill (POP) are not listed for omission. A 20-year-old woman was referred to the endocrinology team, following investigations for syncope by her cardiologist, when ARR was found to be elevated. She was taking POP (Cerelle^®) while having ARR measured. After omitting POP for four weeks, plasma aldosterone concentration was reduced by 52% (from 560 pmol/L to 271 pmol/L, reference range: 100-450 pmol/L), plasma renin concentration increased by 253% (from 3.6 mU/L to 12.7 mU/L, reference range: 5.4-30 mU/L) and ARR reduced from 156 to 21 (-86.5%) (reference range: <80 suggests Conn's unlikely). To the best of our knowledge, this is the first reported case of POP-related false-positive ARR screening for primary hyperaldosteronism. Omission of POP should, therefore, be considered in women undergoing ARR measurement.

Plasma Levels of Adrenocortical Steroids in CAPD and Hemodialysis Patients

CAPD patients appear to have higher levels of plasma renin activity than hemodialysis patients. Increased angiotensin n may result in increased secretion of 18-OH-B and aldosterone by the adrenal zona glomerulosa.

Differences in treatment design between continuous ambulatory peritoneal dialysis (CAPD) and hemodialysis (HD) may affect secretion of adrenocorticosteroids. Ultrafiltration during CAPD is continuous and gradual. Therefore, CAPD patients experience only minor fluctuations in extracellular fluid volume and are usually at or near their estimated dry weight (EDW). In contrast, ultrafiltration in HD patients is rapid but intermittent. Hemodialysis patients approach their EDW only at the end of each treatment period. Hemodialysis patients, therefore, may remain significantly above their EDW for prolonged periods. CAPD allows patients to liberalize their dietary intake of potassium. Some CAPD patients may require potassium supplementation (I). In contrast, HD patients may need to restrict their dietary intake of potassium to prevent potentially lethal hyperkalemia. Heparin is routinely administered during HD but not during CAPD. The present study was designed to determine if these differences in treatment design produce greater stimulation of the adrenal zona glomerulosa in CAPD than in HD patients.

Regulation of plasma aldosterone in anephric and non-nephrectomized patients during hemodialysis treatment

The relationships between plasma aldosterone and changes in plasma potassium, plasma cortisol, plasma sodium, blood volume and body weight have been studied in 6 anephric and 11 non-nephrectomized patients on regular hemodialysis. In all patients, the plasma aldosterone concentration decreased during dialysis. In the anephric patients, a significant correlation (p less than 0.001) was demonstrated between the fall in plasma aldosterone and the fall in plasma potassium (total body potassium depletion). Measurements between consecutive hemodialyses, furthermore, showed a significant correlation (p less than 0.001) in anephric patients between total body potassium repletion (increasing plasma potassium) and the rise in plasma aldosterone. In contrast, the potassium and aldosterone changes did not correlate in the non-nephrectomized group. During dialysis, a decrease was found in all parameters, but no correlation was demonstrable in either group between the changes in plasma aldosterone and the fall in plasma cortisol, sodium, blood volume and body weight. The data in the anephric patients emphasize the important role of potassium in the regulation of aldosterone secretion.

Relationship between plasma aldosterone concentration and plasma potassium in patients with essential hypertension during alprenolol treatment

Plasma aldosterone concentration (PAC), plasma renin concentration (PRC), plasma potassium, plasma sodium and blood pressure (BP) have been measured in 22 patients with essential hypertension before and after treatment for one month with alprenolol. PAC, PRC and BP decreased and plasma potassium increased significantly during treatment. Plasma sodium, however, was unchanged. Changes in PAC were inversely correlated to changes in plasma potassium. No relationship could be demonstrated between PAC and plasma sodium. Mean BP was inversely correlated to PAC during alprenolol treatment, but bot before treatment. No relationship was found between changes in BP and changes in PRC. The results suggest that plasma potassium is an important regulatory factor for aldosterone secretion during alprenolol treatment. Other factors, however, must have a modulating influence and since the renin- angiotensin system is not suppressed to very low values, this system is possibly the most important of these factors. It is suggested that aldosterone secretion is not of primary importance in BP regulation during alprenolol treatment.

The adrenocortical response to angiotensin II infusion in anephric and non-nephrectomized patients on regular hemodialysis

In the present study 8 anephric and 4 non-nephrectomized patients were stimulated with angiotensin II (A-II). In 5 of the anephric patients, an increased plasma aldosterone concentration (PAC) in response to ACTH stimulation had previously been demonstrated. After A-II stimulation, all 8 anephric patients responded with a significant rise in PAC although the increase was less pronounced than in 4 non-nephrectomized patients. In both groups of patients the increase in PAC was correlated to the increase in diastolic and systolic BP and to the A-II dose. Furthermore, in the non-nephrectomized patients, the plasma renin activity showed a significant decline, which was inversely correlated to the increase in PAC. When all 12 patients, regardless of the difference in remaining renin-angiotensin system, were considered as one population, the variable basal levels of PAC correlated significantly to the increase in PAC during A-II and ACTH stimulation. It is concluded that the adrenals of anephric man respond to A-II with an increase in PAC and that the reason for a lower response appears to be the lack of the renin-angiotensin system.

The role of aldosterone in potassium tolerance: studies in anephric humans

Since the role of aldosterone in mediating extrarenal potassium transport remains uncertain, the effect of mineralocorticoid on potassium metabolism was assessed in anephric patients. Seven anephric patients underwent three identical 72-hour periods between hemodialyses during which treatment with either 10 mg/day deoxycorticosterone acetate (DOCA) intramuscularly or 300 mg/day spironolactone orally was compared to a baseline control period. The serum potassium rise, plasma aldosterone, salivary and stool electrolytes were measured in response to potassium loading over 48 hours with a metabolic diet containing 38 mEq/day followed by an "acute" oral potassium load of 0.5 mEq/kg. Acute potassium loading with DOCA resulted in a lower increment in serum potassium than with spironolactone (P less than 0.01). The volume of distribution of the acute potassium load at three hours was 55% of body weight with DOCA, which was significantly greater (P less than 0.05) than with either spironolactone (35%) or control (34%). However, with the dietary load of potassium, the increments in serum potassium measured at 24 and 48 hours (13 hours post-prandial) were similar in all three periods. The volume of distribution of the dietary potassium was not altered by DOCA or spironolactone but had risen to an average of 172% at 24 hours and 243% at 48 hours in the three periods. Plasma aldosterone levels were low, positively correlated to the serum potassium and similar in all three periods without evidence of feedback inhibition by DOCA or stimulated by spironolactone.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoaldosteronism in piglets induced by carbadox

An exploratory study was made of the mechanisms underlying the toxic action of carbadox in young pigs: dehydration, loss of appetite and at autopsy seemingly specific and selective structural alterations of the glomerular zone of the adrenal cortex. Administration of carbadox in the feed, in dosages of 150 ppm (approximately 6 mg X kg-1 b. wt X day-1) caused a rapid decline in the plasma aldosterone levels (to 10% of control) followed by significant changes in the sodium and potassium levels in blood. Characteristic for the toxic action of carbadox are the rapid and seemingly selective and specific alterations in the aldosterone-releasing zona glomerulosa of the adrenals. Our results indicate that with carbadox a functional and possibly reversible extirpation of the adrenal zona glomerulosa can be achieved in pigs.

Augmented aldosterone and insulin responses to potassium infusion in dogs with renal failure

The present study examines acute potassium-induced insulin and aldosterone responses in renal failure, and the role of chronic dietary potassium intake in modifying these acute responses. Plasma aldosterone (PA) and insulin (IRI) responses to acute KCl infusion were examined in control and remnant kidney dogs on two potassium intakes. Dogs (N = 8) received the KCl infusions after 10 days of a 60, and then 10 days of a 200, mEq daily potassium intake during control and after surgical-induced renal failure (CRF). A one hour intravenous infusion of KCl (2 mEq KCl/kg/hr) in dextrose and water was performed with blood samples for PA, IRI, creatinine and electrolytes, and urine for electrolytes and creatinine at 20 minute intervals one hour preceding, during, and after the infusion. Preinfusion PA was higher (P less than 0.05) in controls and CRF dogs on 200 mEq potassium intake compared to 60 mEq potassium intake. The peak incremental responses of PA to KCl infusion were increased (P less than 0.01) in CRF compared to controls on 60 mEq (PA 36 +/- 4.2 vs. 26 +/- 3.0 ng/dl) and 200 mEq (delta PA 49 +/- 5.6 vs. 37 +/- 2.8 ng/dl) potassium intakes. Differences in incremental PA responses in CRF were not due to altered aldosterone metabolic clearance rates, changes in renin, or ACTH activity. Pre-infusion IRI was higher (P less than 0.05) in CRF than control dogs on both potassium diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma concentrations of 18-hydroxycorticosterone and aldosterone in continuous ambulatory peritoneal dialysis and hemodialysis patients

This study explores the hypothesis that the continuous ultrafiltration that accompanies continuous ambulatory peritoneal dialysis (CAPD) produces greater activation of the renin-angiotensin aldosterone axis than does the intermittent ultrafiltration that accompanies thrice weekly hemodialysis (HD). Plasma renin activity (PRA), active renin (AR), total renin (TR), inactive renin (IR), 18-hydroxycorticosterone (18-OH-B), aldosterone (PAC), and cortisol were measured in plasma from CAPD (n = 6) and HD (n = 10) patients. Blood from CAPD patients was sampled at 8 AM after overnight recumbency and at 12 noon after four hours ambulation. Blood from HD patients was sampled immediately pre-HD (8 AM) and post-HD (12 noon) at both 8 AM and 12 noon. PRA (P less than 0.01), AR (P less than 0.01), and AR/TR (100%; P less than 0.01) were higher in CAPD than in HD. IR and TR were not different in the two groups. Plasma 18-OH-B was normal in HD but markedly elevated in CAPD. 18-OH-B was higher in CAPD than in HD at 8 AM (P less than 0.05) and at 12 noon (P less than 0.05). Plasma cortisol was not different in the two groups. We conclude that the greater degree of renin activation in CAPD versus HD contributes to the higher levels of 18-OH-B and PAC observed in CAPD patients.

Hormonal responses to acute volume changes in anephric subjects

The response of plasma aldosterone and cortisol concentrations to acute volume depletion was studied in 18 chronically anephric subjects and four recently nephrectomized subjects. Volume-depleting hemodialysis and hemodialysis without volume depletion produced insignificant changes in plasma aldosterone concentrations in chronically anephric subjects. Failure of volume depletion to increase plasma aldosterone concentrations in these subjects could not be attributed to reductions in plasma potassium concentrations and was in marked contrast to the effect on plasma cortisol concentrations, which increased significantly during volume depletion. Changes in plasma cortisol concentrations exhibited a negative correlation with changes in diastolic blood pressure (r = -0.712, P less than 0.001) and were shown to correspond to similar changes in plasma ACTH concentrations. Comparable increases in plasma cortisol and ACTH concentrations were also demonstrated in the studies on recently nephrectomized subjects, who, in contrast to chronically anephric subjects, exhibited increases in plasma aldosterone concentrations which were concordant with the changes in plasma cortisol and ACTH concentrations. These findings suggest that plasma aldosterone concentrations are regulated by a volume-sensitive mechanism in recently nephrectomized subjects but not in chronically anephric subjects. We interpret these data as evidence of aldosterone responsiveness to ACTH that persists for a limited time only after removal of the stimulus provided by the renin-angiotensin system. Volume-related changes in plasma cortisol and ACTH concentrations occur in the absence of stimulation by a functioning renin-angiotensin system.

Disorders of body fluids, sodium and potassium in chronic renal failure

A stable volume and composition of extracellular fluid are essential for normal functioning of the body. Since the kidney is primarily responsible for regulating extracellular fluid, loss of kidney function should have catastrophic consequences. Fortunately, even with loss of more than 90 percent of renal function, a remarkable capacity to regulate body fluid volumes and sodium and potassium persists. Nevertheless, this capacity is limited to chronic renal disease and this has important consequences for clinical management of these patients. How can sodium and potassium homeostasis be assessed? Methods for evaluating the steady-state regulation of sodium include measurement of body fluids and their distribution in different compartments and measurement of exchangeable and intracellular sodium. Short-term regulation of body sodium can be assessed from measurement of sodium balance during changes in dietary salt. Potassium is predominantly contained within cells and thus the assessment of its regulation requires special emphasis on measurement of steady-state body stores and potassium distribution across cell membranes. However, the methods used to make all of these measurements require assumptions that may not hold in the altered state of uremia. This raises problems in interpretation requiring critical analysis before conclusions can be made regarding sodium and potassium homeostasis in patients with chronic renal failure. This review focuses on abnormalities of body fluids, sodium and potassium in patients with creatinine clearances of less than 20 ml/min due to chronic renal failure and the impact of conservative therapy, dialysis and renal transplantation on these patients.

Effects of angiotensin III and ACTH on aldosterone secretion

ACTH and des-Asp1-angiotensin II (AIII) can raise plasma aldosterone. To assess the threshold for ACTH and AIII stimulated adrenal steroidogenesis we infused ACTH (from 0.03 to 10 ng ACTH/min) and AIII (from 0.1 to 20 ng/kg/min) to dexamethasone pretreated sodium deplete normal subjects and patients with primary aldosteronism, chronic renal failure, and end stage renal disease maintained with continuous ambulatory peritoneal dialysis. Plasma aldosterone in the primary aldosteronism group increased significantly at 0.3 ng ACTH/min compared with 1 to 3 ng ACTH/min in all other groups. The threshold dose for an ACTH stimulated rise in plasma aldosterone was as at least as low as the dose necessary to raise cortisol in all groups. The threshold dose for an AIII stimulated rise in plasma aldosterone was 4 ng/kg/min in normals and between 1 and 3 ng/kg/min in primary aldosteronism. The metabolic clearance rate (MCR) of aldosterone was determined by constant infusion of [3H]-aldosterone. The decline in MCR during AIII infusion contributed less than 15% to the rise in plasma aldosterone in normals and patients with primary aldosteronism.

Mechanism of adrenal angiotensin II receptor changes after nephrectomy in rats

At 48 h after bilateral nephrectomy in rats there is a two- to threefold increase in the number of adrenal angiotensin II receptors and a decrease in Kd of smooth muscle angiotensin II receptors. These changes have been attributed to the absence of circulating angiotensin II. Serum K+, which increases after nephrectomy may be an important and overlooked modulator. Therefore, the present experiments were designed to assess the role of K+ as a regulator of angiotensin II receptors after nephrectomy. Serum K+ was controlled with Na polystyrene sulfonate (Kayexalate), a resin designed to exchange Na+ for K+ in the gastrointestinal tract. Acutely nephrectomized rats were divided into two groups: experimental animals received Kayexalate resin every 12 h for four doses, and controls received Kayexalate exchanged with KCl in vitro before gavage. There was a significant positive correlation serum K+ and aldosterone (r = 0.78, P less than 0.001). Kayexalate maintained a normal serum K+ of 5.9 +/- 0.2 meq/liter (n = 27), aldosterone 25 +/- 3 ng/dl (n = 27) and adrenal receptor concentration of 934 +/- 156 fmol/mg protein (n = 4). Control animals had significantly higher serum K+ of 10.5 +/- 0.4 meq/liter (n = 23), aldosterone 435 +/- 32 (n = 23), and adrenal receptors of 2726 +/- 235 fmol/mg protein (n = 4). There was a linear relationship between serum K+ and number of adrenal receptors (r = 0.87). No such relationship was present in uterine smooth muscle. Therefore, these studies demonstrate that K+ modulates the number of adrenal but not smooth muscle angiotensin II receptors after nephrectomy. This is the first evidence that potassium modulates angiotensin II receptors independently of changes in angiotensin II blood levels.

Stimulation of aldosterone secretion by metoclopramide in humans: apparent independence of renal and pituitary mediation

Metoclopramide (MP), a dopamine antagonist, stimulates secretion of aldosterone by a mechanism which has not been defined. We examined a potential role for either the kidney or the pituitary to mediate MPs effect on aldosterone secretion. Responses to MP administered i.v. were measured in six anephric and six hypopituitary patients as well as in six normal subjects. MP increased the plasma aldosterone concentration (PAC) in normal subjects in a fashion similar to what had previously been reported. MP produced no increase in plasma levels of renin activity (PRA), cortisol, potassium, or sodium. Three of six anephric patients (all of whom had undetectable PRA) responded to MP with increases in PAC; the magnitude of these responses correlated with the plasma potassium concentration. All six hypopituitary patients showed increases in PAC after MP administration. MP increased plasma prolactin levels in normal subjects and anephric patients; one hypopituitary patient had high basal plasma prolactin levels which increased with MP. In conclusion, neither the kidney nor the pituitary is involved in the mechanism for MP stimulated aldosterone production. These observations suggest that MP may act on the adrenal to evoke secretion of aldosterone.

Extrarenal prorenin and renin in anephric patients

Active renin was detected in 6 of 7 anephric patients (mean value: 0.72 +/- 0.27 microU/ml, n = 7; normals: 19.7 +/- 2.4 microU/ml, n = 10), using an assay method without intrinsic acid- or cryoactivation. Prorenin, measured as the difference between plasma renin concentration (PRC) before and after acid-activation in vitro, was present in considerable amounts in all patients (32.4 +/- 3.5 microU/ml; normals: 80.7 +/- 9.7 microU/ml). PRC after cryoactivation at--5 degrees C during 1 week was insignificantly lower than after acid-activation in the patients. There was a linear correlation between PRC after either activation procedure (p less than 0.01). Supine or upright posture did not influence active or inactive renin in the anephric subjects. Our studies show that low but significant levels of active renin and a considerable amount of prorenin are detectable in anephric patients. The data suggest that prorenin in normal subjects in a significant proportion is of extrarenal origin. Orthostasis has no effect on extrarenal active or inactive renin.

Adrenergic modulation of extrarenal potassium disposal

We studied the role of catecholamines in the regulation of potassium homeostasis in nine healthy subjects given intravenous potassium chloride (0.5 meq per kilogram of body weight) in the presence and absence of propranolol. Potassium infusion elevated serum potassium 0.6 +/- 0.09 meq per liter (mean +/-S.E.M.). Addition of propranolol augmented the rise (0.9 +/- 0.05 meq per liter) and prolonged the elevation in serum potassium without decreasing urinary potassium excretion. In a separate study, the same potassium load was administered with a concomitant infusion of epinephrine in five subjects. Epinephrine markedly blunted the increment in serum potassium (0.1 +/- 0.06 meq per liter) while reducing renal potassium excretion. Plasma aldosterone was not altered by the experimental procedures. Serum insulin fell minimally in the presence of propranolol but was unaffected by epinephrine. beta-Adrenergic blockade impairs and epinephrine enhances extrarenal disposal of an acute potassium load. These findings suggest that in patients with impaired potassium disposal, the risk of hyperkalemia may be increased when sympathetic blockade is induced.

Prevalence, pathogenesis, and functional significance of aldosterone deficiency in hyperkalemic patients with chronic renal insufficiency

Our findings indicate that hypoaldosteronism occurs commonly (23/31 patients) in hyperkalemic patients with chronic renal insufficiency and that the deficiency of aldosterone contributes to the pathogenesis of the hyperkalemia. In most patients (83%), hypoaldosteronism could be accounted for by deficient renal secretion of renin, but in some patients (17%) overt renin deficiency did not appear to be present, and therefore other (unidentified) causes of aldosterone deficiency must be invoked. The results also indicate that the urinary excretion rate of aldosterone secretion rate in this group of patients.

Plasma aldosterone, renin activity, and cortisol responses to heat exposure in sodium depleted and repeleted subjects

The effect of 90-min heat exposure (46 degrees C, 35 mbar) on plasma aldosterone (PA) patterns was studied and the respective roles of plasma renin activity (PRA), adrenocorticotropin (ACTH), Na+ and K+ concentrations in the control of PA response were in investigated in eight subjects on a low sodium diet and in five subjects on a high sodium diet. In all subjects, transitory PA increases of varying importance were observed, which were not related to sweat losses (less than 1% bodyweight) or to rectal temperature rise. In sodium-repleted subjects, basal PA and PRA levels as well as heat-induced rises were low (mean PA peak level = 12.62 +/- 1.15 ng/100 ml). They were enhanced by sodium depletion and PA reached a mean peak level of 34.07 +/- 2.73 ng/100 ml. But, in both conditions, the heat-induced PA peaks were 3-times higher than the initial levels. PA correlated with PRA in all but one of the sodium-repleted subjects and in 6 of the 8 sodium-depleted subjects. ACTH release, as measured by plasma cortisol (PC) levels, occurred in those subjects who noted an increased feeling of annoyance and discomfort. Thus, PA correlated positively with PC in 4 sodium-depleted subjects. A high sodium intake improved heat-tolerance. Plasma K+ and Na+ concentrations were not significantly modified by exposure to heat. PA increases can occur without concomitant changes in PRA, PC, K+ or Na+, which suggests that an additional factor may play a role in aldosterone regulation during acute heat exposure.

Effect of potassium chloride on plasma renin activity and plasma aldosterone during sodium restriction in normal man

The present study was designed to evaluate the spectrum of responses of PRA and plasma aldosterone (PAldo) to a range of oral potassium intakes (0 to 300 mEq of potassium chloride per day) in 20 normal human subjects receiving an electrolyte-free diet. Potassium exhibited a dose-dependent natriuretic effect. The results of the PRA studies indicate that normal dietary amounts (50 mEq/day) of potassium chloride do not prevent the increase in PRA with absolute sodium deprivation and that PRA is maximally stimulated on 150 mEq of potassium chloride per day. The rise in PRA is directly correlated with serum potassium concentration. The results of the PAldo studies indicate that potassium chloride deprivation attenuates PAldo increases due to sodium deprivation and that PAldo is maximally stimulated on 150mEq of potassium chloride per day. The rise in PAldo is directly correlated with serum potassium concentration and with PRA. The administration of 300 mEq/day of potassium chloride caused significant hyperkalemia and blunted both PRA and PAldo increases. Our results suggest that potassium chloride has an important role in the regulation of PRA and PAldo, and that only following potassium chloride deprivation is the PRA/PAldo response dissociated.

Possible role for impaired renal prostaglandin production in pathogenesis of hyporeninaemic hypoaldosteronism

A 57-year-old woman with hypertension and moderate renal insufficiency had chronic unexplained hyperkalaemia. Metabolic balance studies confirmed a diagnosis of hyporeninaemic hypoaldosteronism. Two observations suggested that impaired renal prostaglandin production contributed to the pathogenesis of the patient's disorder. Baseline renal-prostaglandin synthesis (as determined by urinary excretion of P.G.E and P.G.F) was was substantially depressed when compared with that in nine normal females. Infusion of low doses of P.G.A1 produced a significant increase in serum-aldosterone and urinary potassium excretion; it also led to a dramatic fall in blood-pressure and serum-potassium. It appears from these studies that a defect in renal prostaglandin synthesis has an important role in the pathogenesis of hyporeninaemic hypoaldosteronism.

Responsiveness of plasma aldosterone: dependency upon basal secretory activity

The responsiveness of plasma aldosterone levels to various stimuli was evaluated in 44 normal subjects, 17 patients with mild to moderate renal failure, 30 patients with terminal renal failure, and 13 anephric subjects. Plasma aldosterone, renin activity (PRA), cortisol, sodium, and potassium levels were measured before and after one hour of upright posture (N = 191); ACTH infusions (N = 76); and angiotensin II infusion (N = 36). Plasma aldosterone responses correlated (r greater than or equal to 0.53; p less than 0.02) with basal plasma aldosterone levels during upright posture in all four groups, with ACTH infusion in all groups except anephric subjects, and with angiotensin II administration in patients with mild to moderate renal failure or patients combined. These relationships were consistently closer than those between aldosterone responses and changes in PRA or basal PRA. However, postural aldosterone responsiveness at any given basal aldosterone level was significantly lower in patients with renal disease than in normal subjects, and this was associated with a parallel impairment in renin responsiveness. In contrast, when related to basal levels aldosterone responsiveness to ACTH or angiotensin II appreared to be comparable in normal subjects and patients with renal disease. Aldosterone responses to posture, ACTH, or angiotensin II did not correlate with associated changes in plasma cortisol, sodium, or potassium levels. These data suggest that basal adrenal secretory activity is a major factor conditioning aldosterone responsiveness to various stimuli in normal subjects as well as in patients with renal disease.

Studies of renin-aldosterone axis in stable normotensive and hypertensive renal allograft recipients

Functional aspects of the renin-aldosterone axis were investigated in long-term normotensive and hypertensive renal allograft recipients. Unstimulated plasma renin and aldosterone levels were within control range in all patients and rose significantly in response to sodium depletion. However, no difference in the stimulated renin and aldosterone values between normotensive and hypertensive patients was noted. Baseline aldosterone secretory rates were elevated in all patients, but were higher in hypertensive patients than in normotensive patients. In both groups sodium depletion failed to augment this already elevated aldosterone secretion rate. Possibly, changes in the body pool and/or metabolic clearance rate of aldosterone account for elevations in plasma levels despite a relatively fixed secretory rate, though the role played by the lack of normal innervation of the kidneys cannot be ignored. It is unknown whether these observations may be causal or affected by other presently unknown or unmonitored factors. This in part may reflect unfolding problems in the understanding of nonrenal transplant hypertension.

Potassium-renin-aldosterone relationships during the first year of life

In order to gain insight into factors controlling aldosterone secretion during the first year of life, we studied the relationships between PRA, serum potassium, sodium, and serum aldosterone levels. While we found a dissociation during the early neonatal period, there was a high degree of correlation between serum aldosteron, PRA, and serum potassium by 3 to 12 months of age. This suggests that aldosterone secretion in the 3- to 12-month-old child, as in adults, is regulated by the circulating levels of potassium and angiotensin II.

Plasma aldosterone during extracellular fluid volume expansion in patients on regular haemodialysis

The influence of extracellular fluid volume expansion on the plasma aldosterone concentration (PAC) was investigated in five anephric and six non-nephrectomized patients on regular haemodialysis, and compared to a control group of four anephric and four non-nephrectomized patients. Plasma-renin activity, cortisol, Na+, and K+ were measured together with the PAC during the investigation. In anephric patients the PAC remained constant during the control period as well as during extracellular fluid volume expansion by infusion of 350 mmol of 20% mannitol. In the non-nephrectomized patients PAC diminished after mannitol infusion. The decline in PAC was correlated with the basal levels of PAC and the plasma renin activity. It is concluded that 5% extracellular fluid volume expansion has no direct influence on the regulation of PAC in patients without the renal renin-angiotensin system and that the regulation of PAC in anephric patients in the present investigation is probably mediated by changes in potassium and ACTH.

Renin and aldosterone suppression in the antihypertensive action of clonidine

In 18 hypertensive patients receiving a constant (100 mEq/day) sodium diet, treatment with clonidine (0.3 mg/day for 5 days) decreased blood pressure in 11 patients with high and normal renin levels and 7 with low renin levels. The high and normal renin group had early and rapid reductions in blood pressure and plasma renin activity. In contrast, the low renin group had a more gradual hypotensive response and only a small absolute decrease in plasma renin. For all patients, pretreatment renin levels were related to the initial decrease in blood pressure but not to the reductions measured after 5 days. Thus, two mechanisms of action of clonidine are possible, one related to acute inhibition of the renin-angiotensin system in patients with high and normal renin levels and another that is independent of renin mechanisms and occurs in all hypertensive patients. In six additional patients with high renin levels induced by prior sodium depletion (10 mEq/day sodium diet), clonidine did not reduce blood pressure or renin, thus indicating that the suppressive action of this agent on renin pressor mechanisms occurs only in patients whose elevated renin levels are intrinsic to hypertension and unrelated to sodium depletion. Of the 18 patients receiving a normal sodium diet, 13 were classified as responding to treatment (decrease in both systolic and diastolic pressures of at least 10%). The five nonresponders had greater weight gain and higher values for aldosterone excretion. For all patients, there was a significant correlation between decrements in blood pressure and in aldosterone, suggesting that the countervailing effects of fluid accumulation on blood pressure in nonresponding patients resulted from a failure of aldosterone to be suppressed. Changes in aldosterone, in turn, correlated significantly with changes in renin. Thus, the antirenin effect of clonidine enhances its antihypertensive action not only by acutely ablating renin-angiotensin pressor mechanisms, but also by inhibiting aldosterone production and thereby minimizing longer-term reactive volume retention during treatment.

Response of aldosterone and blood pressure to angiotensin II infusion in anephric man. Effect of sodium deprivation

Angiotensin II, infused intravenously, increased plasma aldosterone concentration in two of six anephric subjects taking their usual dietary quantities of sodium. After 3 days of dietary sodium restriction and weight-reducing hemodialysis, the aldosterone response to infused angiotensin II in the two previously reactive subjects was enhanced, while the four previously unreactive subjects also showed a rise in plasma aldosterone. Before and after sodium depletion the anephric subjects were less responsive than normal subjects. Even when sodium-depleted, the anephrics showed no further rise in plasma aldosterone when arterial plasma angiotensin II was increased by infusion to concentrations greater than 50-199pg/ml, in contrast to sodium-depleted normals who show progressive aldosterone responses with plasma angiotensin II concentrations up to at least 370pg/ml. Before the infusion of angiotensin II, arterial plasma renin, angiotensin II, and aldosterone were detectable in the anephrics, but were unchanged by dietary sodium restriction or weight-reducting hemodialysis. Sodium depletion caused significant falls in weight, plasma sodium, and blood pressure, but no changes in plasma potassium or cortisol. Increases in blood pressure in relation to increments of arterial plasma angiotensin II were unaffected by sodium depletion, as might be expected in the absence of a rise in endogenous angiotensin II.

Hepatorenal syndrome: a disease mediated by the intrarenal action of renin

The functional renal failure accompanying advanced liver disease is characterized by azotemia, a urine of very low sodium concentration and systemic hypotension with decreased renal perfusion and high renal vascular resistance. Patients with this disorder have a markedly reduced ability to excrete free water and develop hyponatremia, ascites and edema. It is postulated that this renal dysfunction is due to hepatic failure to make renin substrate. Renin released from the kidney is thus unable to exert its pressor effect. The resultant hypotension and renal hypoperfusion continue to stimulate excessive synthesis and release of renin. It is postulated that the overdriven renal renin system increases renovascular resistance at the level of the glomerular arterioles. This causes decreased renal blood flow and decreased glomerular filtration rate leading to salt and water retention and azotemia. Since no renin substrate is available for human infusion, this hypothesis could be tested either by infusion of angiotensin II to restore systemic blood pressure and renal perfusion or by beta adrenergic blockade with propranolol to attempt to decrease the intrarenal effects of renin, restore glomerular blood flow and filtration and thus return of renal function.

Effect on aging on plasma renin and aldosterone in normal man

The influence of aging on the renin-angiotensin-aldosterone system was evaluated by comparing young (20 to 30 yr) with elderly (62 to 70 yr) healthy subjects. Despite comparable body sodium-fluid balance in the two age groups, serum renin concentration, plasma renin activity and aldosterone concentrations were lower in the elderly. The age-related decreases in circulating renin and aldosterone concentrations were slight while subjects were supine and receiving normal sodium intake; when upright and during sodium depletion, they were more pronounced. Inverse renin-blood pressure interrelations were noted during two of four study conditions involving normal sodium intake or mild sodium depletion (r = --0.44 and --0.47, respectively), but not during progressive sodium depletion. Plasma renin levels were decreased in the elderly regardless of the presence or absence of an inverse relationship with blood pressure. Aldosterone and cortisol responses to corticotropin infusion were unaltered in the elderly. It is concluded that aging may cause a decrease in circulating renin, with parallel lowering of plasma aldosterone concentrations.

Control of aldosterone responsiveness in terminal renal failure

Control of aldosterone responsiveness in terminal renal failure. Plasma aldosterone concentration in 30 hemodialysis patients correlated closely with renin concentration, renin activity or renin and potassium concentrations combined (r is greater than or equal to 0.62; P is less than 0.01), and increased consistently in response to upright posture or corticotropin administration. Aldosterone response to hemodialysis was variable. Significant correlations (r is greater than or equal to 0.65; P is less than 0.01) were demonstrated between postural plasma aldosterone and renin responses, between aldosterone responses to corticotropin and basal plasma aldosterone or renin and potassium values, between hemodialysis-induced changes in plasma aldosterone and those in potassium or renin; but not between various indexes of heparin treatment and aldosterone activity. Bilateral nephrectomy reduced basal plasma renin and aldosterone concentrations and aldosterone responsiveness in five preoperatively normoreninemic or hyperreninemic patients, but not in a hyporeninemic patient. These results demonstrate the complementary roles of circulating renin and potassium in the control of aldosterone release under basal and stimulatory conditions in patients with terminal renal failure. Administration of heparin in dosages used during long-term hemodialysis does not appear to significantly interfere with aldosterone control.