Humoral stimulation of adrenal cortical secretion

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Neural circuits underlying thirst and fluid homeostasis

Thirst motivates animals to find and consume water. More than 40 years ago, a set of interconnected brain structures known as the lamina terminalis was shown to govern thirst. However, owing to the anatomical complexity of these brain regions, the structure and dynamics of their underlying neural circuitry have remained obscure. Recently, the emergence of new tools for neural recording and manipulation has reinvigorated the study of this circuit and prompted re-examination of longstanding questions about the neural origins of thirst. Here, we review these advances, discuss what they teach us about the control of drinking behaviour and outline the key questions that remain unanswered.

Prion protein gene variability in Spanish goats. Inference through susceptibility to classical scrapie strains and pathogenic distribution of peripheral PrP(sc.)

Classical scrapie is a neurological disorder of the central nervous system (CNS) characterized by the accumulation of an abnormal, partially protease resistant prion protein (PrP(sc)) in the CNS and in some peripheral tissues in domestic small ruminants. Whereas the pathological changes and genetic susceptibility of ovine scrapie are well known, caprine scrapie has been less well studied. We report here a pathological study of 13 scrapie-affected goats diagnosed in Spain during the last 9 years. We used immunohistochemical and biochemical techniques to discriminate between classical and atypical scrapie and bovine spongiform encephalopathy (BSE). All the animals displayed PrP(sc) distribution patterns and western blot characteristics compatible with classical scrapie. In addition, we determined the complete open reading frame sequence of the PRNP in these scrapie-affected animals. The polymorphisms observed were compared with those of the herd mates (n = 665) and with the frequencies of healthy herds (n = 581) of native Spanish goats (Retinta, Pirenaica and Moncaina) and other worldwide breeds reared in Spain (Saanen, Alpine and crossbreed). In total, sixteen polymorphic sites were identified, including the known amino acid substitutions at codons G37V, G127S, M137I, I142M, H143R, R151H, R154H, R211Q, Q222K, G232W, and P240S, and new polymorphisms at codons G74D, M112T, R139S, L141F and Q215R. In addition, the known 42, 138 and 179 silent mutations were detected, and one new one is reported at codon 122. The genetic differences observed in the population studied have been attributed to breed and most of the novel polymorphic codons show frequencies lower than 5%. This work provides the first basis of polymorphic distribution of PRNP in native and worldwide goat breeds reared in Spain.

Direct renin inhibition: extricating facts from façades

The renin–angiotensin system (RAS) affects vascular tone, cardiac output and kidney function. By these means the RAS plays a key role in the pathogenesis of arterial hypertension. As a result, RAS inhibition is highly effective not only in lowering blood pressure but also in reducing kidney disease progression (particularly when associated with proteinuria) and cardiovascular events.

Among RAS blocking agents, direct renin inhibitors have shown not only excellent efficacy in hypertension control but also pharmacologic tolerance that is comparable with other renin–angiotensin suppressors. Indeed, aliskiren, the only direct renin inhibitor available is effective in controlling blood pressure as monotherapy or in combination with other antihypertensive drugs, irrespective of patient’s age, ethnicity or sex. It is also effective in patients with metabolic syndrome, obesity and diabetes. Long-term studies comparing ‘hard endpoints’ of aliskiren therapy versus treatment with other RAS inhibitors, including cardiac and kidney protection, are currently ongoing. Combined with other antihypertensive agents, aliskiren not only improves their hypotensive response but may also lessen the adverse effects of other drugs. In high-risk patients, however, precautions should be taken when combining two or more renin–angiotensin inhibiting agents, as tissue perfusion may be highly renin-dependent in these patients and serious adverse side effects could take place.

Local inhibition of nitric oxide temporarily stimulates aldosterone secretion in conscious sheep in vivo

The effect of localized blockage of endogenous nitric oxide (NO) on basal aldosterone secretion was studied in conscious sheep with autotransplanted adrenal glands. We have shown that infusion of the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 130 microg/l blood flow) significantly stimulated basal aldosterone secretion rate (ASR). This stimulatory effect was seen up to 4 h of infusion. Beyond this time point, however, the elevated ASR level was not sustained, and it was seen to drop markedly to lower than control values at 5 h. L-NAME had no effect on cortisol secretion rate (FSR) during the first 4 h of infusion, but a significant reduction in FSR was seen by the 8-h time point. Adrenal blood flow was consistently decreased in association with long L-NAME infusion. Additionally, L-NAME was shown to have no effect on aldosterone secretion when infused systemically. We conclude that the relationship between NO and aldosterone secretion is an inhibitory one, in which NO seems to have a negative effect on basal aldosterone secretion.

Functional glucocorticoid receptors in the mesonephros of the ovine fetus

BACKGROUND

At 27 days of gestation in the ovine fetus (term = 145 to 150 days), the only kidney is the mesonephros, and allantoic fluid represents fetal urine. The hypothesis tested in this study was that functional glucocorticoid receptors (GRs) are present in this early mesonephric kidney.

METHODS

Pregnant ewes, between 26 and 30 days, were infused with saline, dexamethasone (0.48 mg/hour), cortisol (5 mg/hour), or aldosterone (10 microg/hour) for 48 hours and were then killed for collection of fetuses and fetal fluids. GR mRNA was measured by real-time polymerase chain reaction in whole fetuses, and the location of gene expression was determined by hybridization histochemistry.

RESULTS

Significant changes in allantoic fluid composition were produced by the exposure of the fetus to maternally infused synthetic (dexamethasone) and natural (cortisol) glucocorticoids, over a period of two days, compared with fetuses of ewes infused with vehicle (isotonic saline; N = 8) or aldosterone (N = 8). Volume of fluid was unchanged by any treatment, but both dexamethasone (N = 10) and cortisol (N = 8) caused significant (P < 0.05) decreases in sodium and chloride concentrations and increases in concentrations of potassium, urea, glucose, and fructose. GR mRNA was detected in equivalent concentrations in the whole fetuses of saline, dexamethasone, and cortisol treatments. The GR mRNA levels were significantly decreased in the aldosterone group. By hybridization histochemistry, GR mRNA was detected in most of the tubular cells of the mesonephros.

CONCLUSION

These results suggest that functional GRs are present in the early ovine mesonephros.

A role for T-type Ca2+ channels in the synergistic control of aldosterone production by ANG II and K+

Independently, plasma K+ and ANG II stimulate aldosterone secretion from adrenal glomerulosa (AG) cells, but together they synergistically control production. We studied mechanisms to mediate this synergy using bovine AG cells studied under physiological conditions (in 1.25 mM Ca2+ at 37 degrees C). Increasing K+ from 2 to 5 mM caused a potentiation of ANG II-induced aldosterone secretion and a substantial membrane depolarization ( approximately 21 mV). ANG II inhibited a K+-selective conductance in both 2 and 5 mM K+ but caused only a slight depolarization because, under both conditions, membrane potential was close to the reversal potential of the ANG II-induced current. ANG II activated calcium/calmodulin-dependent protein kinase II (CaMKII) equivalently in 2 and 5 mM K+. However, CaMKII activation caused a hyperpolarizing shift in the activation of T-type Ca2+ channels, such that substantially more current was elicited at membrane potentials established by 5 mM K+. We propose that synergy in aldosterone secretion results from K+-induced depolarization and ANG II-induced modulation of T-type channel activation, such that together they promote enhanced steady-state Ca2+ flux.

Angiotensin and aldosterone

The object of this review is to describe the role of the renin-angiotensin system in control of aldosterone secretion. The review focuses on the roles of the circulating renin-angiotensin (RAS) system, the activity of which is determined predominantly by control of renin secretion from the kidney and on the role of the intra-adrenal RAS. Angiotensin can bind to two types of G protein coupled receptors, the AT1 and AT2 receptors. Both receptors are found on cells from the zona glomerulosa, the site of aldosterone synthesis. Angiotensin II acting via the AT1 receptor stimulates the synthesis of aldosterone at early and late steps in the pathway. Its effect on aldosterone is influenced by a number of other factors such as plasma potassium levels, sodium status, other peptides such as ANP and adrenomedullin and proadrenomedullin N-terminal peptide. All components of the RAS are found in the adrenal gland. The activity of this intra-adrenal RAS is unmasked and amplified in nephrectomised animals. Aldosterone controls sodium transport across epithelial cells, but recently novel effects on the heart have been described.

Hypothesis: aldosterone is synthesized by an alternative pathway during severe sodium depletion. 'A new wine in an old bottle'

1. The last three steps of aldosterone biosynthesis, 11 beta-hydroxylation, 18-hydroxylation and 18-oxidation, have been demonstrated to be catalysed by one enzyme, which is the cytochrome P450(11 beta) (CYP11B) in cow, pig, sheep and bullfrog or cytochrome P450aldo (CYP11B2) in rat, human, mouse and hamster. 2. The related enzyme P450(11 beta) (CYP11B1) from rat, human, mouse and hamster adrenals displays 11 beta-hydroxylation and 18-hydroxylation activities, but not 18-oxidation activity in vitro. No such enzyme has been reported in the cow, pig or sheep to date. 3. Data showing the dissociation of aldosterone secretion from plasma angiotensin II (AngII) levels indicate the presence of other factor(s) that regulate aldosterone biosynthesis in response to changes in body sodium status. Thus, we propose the existence of a 'sodium status factor' that regulates aldosterone biosynthesis in addition to AngII, K+, adrenocorticotropic hormone and atrial natriuretic peptide. 4. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to a pathway using 18-hydroxy-deoxycorticosterone (18-OH-DOC) rather than corticosterone as an intermediate. This switch may be mediated via the putative 'sodium status factor'. 5. Two models of the hypothesis will be discussed in this paper: (i) a 'one-enzyme' model; and (ii) a 'two-enzyme' model. 6. The one-enzyme model proposes that P450aldo (P450(11 beta) as in the case of the cow, sheep and pig) changes its enzymatic activity during severe sodium deficiency (i.e. switching to the alternative aldosterone biosynthesis pathway). 7. The two-enzyme model proposes that, under normal circumstances, P450aldo synthesizes aldosterone from deoxycorticosterone, while during severe sodium deficiency the P450(11 beta) provides the substrate (i.e. 18-OH-DOC) for the P450aldo.

A compartmental model of acute stimulation of aldosterone secretion in vivo by potassium and ANG II

Conscious sheep with an adrenal autotransplant were used to study the relationship between acute change in K+ concentration and acute change in aldosterone secretion rate (ASR). The kinetics of K+ within the adrenal circulation were shown to be consistent with distribution within a single compartment. In contrast, change in ASR during and after KCl infusion was consistent with a two-compartment model, where ASR was a sigmoidal function of concentration of K+ (or other unidentified agent) in the second, or "effect," compartment. Prior work on the relationship between acute change in angiotensin II (ANG II) concentration and acute change in ASR was extended by investigating the interaction of K+ and ANG II in the control of ASR. The results of this study indicate that acute change in ANG II concentration may cause an inhibition of the usual response of the adrenal to acute change in K+ concentration.

Pathophysiology of renovascular hypertension

Renovascular hypertension has its experimental counterpart in the two-kidney, one clip model (Goldblatt hypertension). From the study of this model, a general pathophysiological scheme has evolved suggesting that temporal stages in the development and maintenance of hypertension are regulated by complicated hormonal and neural interrelations. The central roles played by the renin-angiotensin system and the renal nerves is discussed as they relate to other hormones. In addition, the possible contribution of converting enzyme inhibitors to understanding the pathophysiology of this condition is discussed.

Renal effects of aldosterone in the sodium bicarbonate infused rat

The present study investigated the renal function in male Sprague-Dawley rats receiving continuous NaHCO3 (0.077 M) infusion. The renal effects of aldosterone administration in this preparation were also examined. Continuous NaHCO3 infusion significantly (p less than 0.01) depressed plasma aldosterone concentration to 2.36 +/- 1.22 nmol (n = 8) when compared to saline infused rats (4.36 +/- 0.72 nmol, n = 7). The low plasma aldosterone levels in HCO3- infused rats was associated with renal loss of large amounts of K+ and hypokalaemia. Aldosterone administration (42 pmol/min) for 2 h significantly (p less than 0.01) reduced the Na+ excretion rate in bicarbonate infused rats from a mean peak of 9.82 +/- 1.16 to 5.16 +/- 1.20 mumol/min (n = 8). Aldosterone administration did not alter renal excretion in saline-infused rats. It is concluded that NaHCO3 loading depressed endogenous aldosterone secretion, and that this lowered endogenous plasma aldosterone level allows the mineralocortoid effect of exogenous aldosterone to be observed.

Hyperinsulinemia and the aldosterone and pressor responses to angiotensin II

To determine whether hyperinsulinemia alters angiotensin II-mediated aldosterone secretion, the increase in plasma aldosterone after intravenous angiotensin II (5, 10, and 20 ng/kg/min for 15 minutes each) was measured before and after euglycemic hyperinsulinemia in seven chronically instrumented dogs. In a random sequence on 4 successive days, dogs received either 0, 2, 4, or 8 milliunits/kg/min insulin. Euglycemic hyperinsulinemia, at all insulin doses, resulted in a significantly greater (p less than 0.01) change in the angiotensin II-stimulated increments of plasma aldosterone than was observed when angiotensin II was administered alone. However, there was no dose-dependence of insulin's effect on angiotensin II-stimulated aldosterone. The effect of weight gain on the angiotensin II response was also evaluated in five dogs. After weight gain, euglycemic hyperinsulinemia augmented angiotensin II-stimulated aldosterone to the same magnitude that was observed before weight gain. Possible mechanisms whereby insulin could increase angiotensin II-stimulated aldosterone production include: increased intracellular potassium, reduced plasma free fatty acids, and a direct action of insulin to induce increased adrenal steroidogenesis. In addition to altering the angiotensin II-aldosterone dose-response curve, hyperinsulinemia also increased the pressor action of angiotensin II. In contrast to the angiotensin II-aldosterone response, progressive hyperinsulinemia resulted in a progressive increase in the pressor response to angiotensin II. The increased pressor response is probably due to an increased activation of the sympathetic nervous system by insulin.

Intracerebroventricular and systemic saralasin used to investigate angiotensin-elicited activation of the pituitary-adrenocortical axis in the goat

Intracerebroventricular (ICV) infusion of the competitive inhibitor for angiotensin II (AII), saralasin, (13 pmol kg-1 min-1), preceding and outlasting the intravenous (i.v.) infusion of AII (40 pmol kg-1 min-1) extinguished the elevation in plasma cortisol (PC) obtained in response to just the i.v. AII infusion. The corresponding i.v. infusion of saralasin did not visibly influence the AII-induced elevation of PC, whereas bilateral intracarotid infusions of the inhibitor tended to reduce the response. The ICV administration of the inhibitor also significantly reduced the rise in plasma aldosterone (PA) seen as an effect of the i.v. AII. Paradoxically, however, the intravascular infusions of saralasin conspicuously augmented the rise in PA obtained after the simultaneous i.v. infusion of AII. It is concluded that cerebral mediation of the ACTH-cortisol response to systemic AII occurs at sites accessible to inhibition from both sides of the blood-brain barrier, and that also the PA response to blood-borne AII may be to some extent cerebrally mediated.

Low-renin hypertension of childhood

Measurement of plasma renin activity (PRA) and aldosterone with a knowledge of dietary sodium balance is critical to the diagnostic evaluation of childhood hypertension. Disturbances of steroid production, regulation, metabolism and sensitivity have been implicated in the pathogenesis of low-renin hypertension in childhood. Prompt initiation of treatment is essential because the hemodynamic changes caused by long-standing hypertension may become irreversible. The clinical features and hormonal findings of the most important adrenocortical disorders associated with low-renin hypertension in childhood are summarized.

Central serotonergic stimulation of aldosterone secretion

Serotonin stimulates aldosterone secretion both in vitro and in vivo, and serotonin antagonism decreases plasma aldosterone levels in patients with idiopathic aldosteronism. This study was designed to assess the effects of the serotonin precursor, 5-hydroxytryptophan (5HTP), upon aldosterone secretion in man, and to determine whether stimulatory effects of 5HTP are mediated through the central nervous system. Oral 5HTP, administered as a single 200-mg dose, increased plasma aldosterone levels from 4.7 +/- 0.6 to 13.3 +/- 2.8 ng/dl in dexamethasone-pretreated, normal volunteers. Peripheral inhibition of decarboxylation of 5HTP, achieved by pretreatment with carboxydopa, 25 mg three times daily for 3 d, significantly increased the stimulatory effects of 5HTP on aldosterone levels (P less than 0.001). No change in aldosterone levels occurred in subjects who received placebo after pretreatment with dexamethasone and carboxydopa. Increased aldosterone was not accompanied by increases in plasma levels of renin activity, potassium, or ACTH. Plasma levels of 5HTP were markedly increased by carboxydopa pretreatment, but peak plasma levels of serotonin were not significantly altered. Four patients with idiopathic aldosteronism all had an increase in plasma aldosterone levels after 5HTP administration, whereas the response in four patients with aldosterone-producing adenoma was variable. Incubation of isolated human and rat adrenal glomerulosa cells with serotonin resulted in increased aldosterone secretion by both sets of cells, whereas 5HTP was ineffective in stimulating aldosterone secretion in vitro. We conclude that central serotonergic pathways are involved in the stimulation of aldosterone induced by administration of 5HTP. This mechanism may be an important etiologic factor in the hypersecretion of aldosterone that occurs in patients with idiopathic aldosteronism.

Role of angiotensin II in potassium-mediated stimulation of aldosterone secretion in the dog

Potassium is known to enhance the aldosterone-stimulating action of angiotensin II. Such a synergistic interaction of potassium with angiotensin II could represent an action by angiotensin II to potentiate potassium as a stimulus. To examine for this effect of angiotensin II on potassium, plasma aldosterone levels were measured before and after an infusion of potassium chloride (15 meq i.v.) into dogs without and with prevention of angiotensin II formation by captopril, an angiotensin converting-enzyme inhibitor. In addition, responses to potassium were measured in a group of dogs receiving angiotensin II plus captopril. After potassium infusion, control dogs showed an increase of 7.7 +/- 1.9 (SEM) ng/dl (P less than 0.001) in the level of plasma aldosterone. In contrast, captopril-treated dogs showed no change in plasma aldosterone concentration in response to potassium. When angiotensin II was administered to captopril-treated dogs responsiveness to potassium administration was restored (plasma aldosterone concentration increased by 7.4 +/- 2.1 ng/dl, P less than 0.002). ACTH stimulated aldosterone secretion despite captopril treatment (P less than 0.001), however, ACTH produced a greater increase in the plasma aldosterone concentration in controls than in captopril-treated animals. It is evident from these results that stimulation of aldosterone secretion by potassium is considerably enhanced by angiotensin II. There appears to exist an important interdependence of these stimuli in the regulation of aldosterone secretion.

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.

Ageing and circadian rhythm of plasma renin and aldosterone

Five men and 8 women, 60-69 yr of age, and 4 men and 5 women, 17-37 yr of age, volunteered for this exploration of possible age-related changes in circadian-rhythm (CR) characteristics of radioimmunoassayable plasma renin (PRA) and aldosterone (PA). Blood was drawn at 06.00, 08.00, 12.00, 18.00, 20.00 and 24.00 from recumbent subjects on a habitual sodium intake of 120-140 mEq/24 h. Time-qualified data of PRA and PA, fitted by a 24-h cosine curve, were summarized by a population mean-cosinor method. Circadian characteristics were compared by a multivariate analysis using Hotelling's t2 test. Rhythmometry reveals in the elderly women a lower mesor (P less than 0.001) and amplitude (P = 0.036) of the CR in PRA and a higher mesor and amplitude (P = 0.021 and P = 0.020, respectively) of the PA-CR. The PRA acrophase is delayed (P less than 0.001) in the elderly women (04.40 vs. 08.04) while the timing of the PA acrophase is similar in the age groups of women compared (05.52 vs. 05.20). These differences found in women were not observed in the smaller groups of men. The seventh decade of life may be characterized by an internal circadian desynchronization between the major components of the renin-angiotensin-aldosterone system. A sex-dependent amplification of the extent of circadian variation in aldosterone may precede a decrease in the circadian amplitude occurring during the eighth decade of life, as a sign of the adrenopause in women.

Effect of sustained hypernatraemia on the renin-aldosterone system in the dog

1. To determine if increases in plasma sodium concentration P[Na] have any sustained effects of the renin-aldosterone system, P[Na] was increased in a group of six dogs over a period of 6 days by increasing sodium intake from 10 to 200 mmol per day while a fixed 700 ml per day water intake was maintained along with a continuous i.v. infusion of antidiuretic hormone (ADH) at a rate of 2.4 units per day. 2. P[Na] rose from 137.3 +/- 2.0 to 153.6 +/- 6.5 mmol/l during the high intake period. Plasma potassium concentration, 22Na space, and mean arterial pressure all remained near control levels in response to Na loading. 3. Plasma renin activity (PRA) averaged 1.0 +/- 0.1 ngAI/ml per hour on the final low Na day and fell transiently to 0.6 +/- 0.2 ngAI/ml per hour on the first day of sodium loading. For the duration of the study it remained at the control level. Plasma aldosterone concentration fell from the low Na level of 15.4 +/- 2.4 ng/100 ml to 10.5 +/- 1.5 ng/100 ml on the final day of high Na intake. 4. We conclude that increases in P[Na] in the absence of concomitant changes in P[K], 22Na space and MAP do not have a sustained effect on control of renin release but may exert a negative effect on aldosterone secretion.

Computer modelling of aldosterone regulation in patients on regular hemodialysis

To evaluate the relative influence of changes in plasma renin activity, potassium, ACTH, and sodium concentrations on the secretion of aldosterone, a multifactorial analysis was performed on different sets of investigations in anephric as well as non-nephrectomized patients on regular hemodialysis. During steady-state conditions the relationship between the stimulating effect of each of these factors and combinations between these factors and the resultant plasma aldosterone concentration was analyzed. Linear models could not explain all variations in plasma aldosterone, especially not a variation found within patients. The stimulus-response curve is therefore probably non-linear and at least one or more additional factors may take part in the aldosterone regulation.

Angiotensin alters 45Ca2+ fluxes in bovine adrenal glomerulosa cells

Angiotensin II stimulated 45Ca2+ release from bovine adrenal glomerulosa cells. It also decreased the influx of 45Ca2+ into glomerulosa cells. The effects were observed within 2 min of hormone addition and were blocked by Saralasin a competitive inhibitor of angiotensin. Des-Phe8-angiotensin II, a biologically inert analog, was inactive in this system. Angiotensin II also inhibited the influx of 133Ba2+ and 54Mn2+, whereas 51Cr6+ and 57Co2+ were unaffected. Alterations in 45Ca2+ fluxes were seen with concentrations of angiotensin that stimulate aldosterone biosynthesis in bovine glomerulosa cell preparations. These results suggest that calcium plays a key role in angiotensin-stimulated aldosteronogenesis.

The blood volume and the renin-angiotensin-aldosterone system following open-heart surgery

The circulating blood volume changes, plasma electrolytes, aldosterone as well as plasma-renin-activity (PRA) were studied in 14 patients following open-heart surgery with cardiopulmonary bypass (CPB) and in 14 patients following cardiac surgery without CPB. In both the groups a postoperative decrease of circulating blood volume was observed. This decrease occurred in spite of the positive fluid balance, and so a shift of fluid from vascular to extravascular compartment was likely. In the bypass group the plasma aldoserone level rose immediately after the operation and reached the peak on the first postoperative day. In the non-bypass group the aldosterone level started to fall after the operation, and reached the lowest level on the third postoperative day. The pattern of the postoperative PRA changes was almost identical with the aldosterone level changes in both the groups studied, which suggests that the activation of renin-angiotensin-aldosterone axis might be responsible for the observed plasma aldosterone changes.

Characterisation of an adrenal zona glomerulosa-stimulating component of posterior pituitary extracts as alpha-MSH

The secretion of aldosterone from the zona glomerulosa of the mammalian adrenal cortex is stimulated by ACTH, potassium, angiotensin II and III, growth hormone, serotonin and E series prostaglandins. Some experimental and clinical studies suggest that additional stimulants of the zona glomerulosa must exist, possibly including pituitary factors other than ACTH. The possibility that posterior pituitary extracts may contain a zona glomerulosa stimulant was first suggested 20 years ago, but has since received little attention. We describe here the purification from posterior pituitary extracts of activities that stimulate rat glomerulosa cells and whole tissue in vitro. One of the active compounds has been identified as alpha-MSH (melanocyte stimulating hormone).

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.