Effects of dibutyryl adenosine 3',5'-monophosphate, angiotensin II, and atrial natriuretic factor on phosphorylation of a 17,600-dalton protein in adrenal glomerulosa cells

Rat adrenal glomerulosa cells were incubated with [32P]phosphate and (Bu)2AMP (dbcAMP), angiotensin II, and atrial natriuretic factor (ANF). Incorporation of [32P]phosphate into cellular proteins was analyzed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. dbAMP stimulated phosphorylation of a 17.6K protein, while angiotensin II did not stimulate it. ANF did not affect the protein phosphorylation, whether the cells were in the basal state or stimulated by dbcAMP or angiotensin II. On the other hand, ANF markedly inhibited angiotensin II-stimulated aldosterone production, but only slightly inhibited dbcAMP-stimulated aldosterone. These results suggest that in rat adrenal glomerulosa cells phosphorylation of the 17.6K protein may have a relationship with the stimulatory effect of cAMP on aldosterone production; however, neither angiotensin II nor ANF affected the phosphorylation of this protein, and phosphorylation of the 17.6K protein is not an obligatory step in the regulation of aldosterone production.

Effects of alpha-human atrial natriuretic polypeptide, sodium nitroprusside and dibutyryl cyclic GMP on aldosterone production in bovine zona glomerulosa cells

When bovine adrenal zona glomerulosa cells were incubated with alpha-human atrial natriuretic polypeptide (alpha-hANP), the basal aldosterone production in the cells was hardly affected, although the angiotensin II- or K+-stimulated production was completely inhibited. alpha-hANP was found to cause the generation of cyclic GMP in the cells. When the cells were incubated with sodium nitroprusside, the drug inhibited the angiotensin II- or K+-stimulated aldosterone production, and also generated cyclic GMP in the cells. In contrast, dibutyryl cyclic GMP was found to be a stimulator of the aldosterone response rather than an inhibitor. The results obtained in this study cast doubt on the role of cyclic GMP as an intracellular second messenger for the action of ANP on aldosterone secretion.

Adrenal renin: a possible local hormonal regulator of aldosterone production

The complete renin-angiotensin system is present in the adrenal cortex: prorenin, renin, angiotensinogen, angiotensin I and II, and converting enzyme. Most of the renin found is probably synthesized there since the renin concentration increases after nephrectomy, and the mRNA for renin is present. The renin-angiotensin system has the highest activity in the zona glomerulosa cells, the site of aldosterone formation. A low-sodium diet or a high-potassium diet, or nephrectomy markedly increases the adrenal renin concentration in the zona glomerulosa cells without any effect on the fasciculata-medullary cells. There is a close correlation between adrenal renin and aldosterone production. The adrenal renin angiotensin system may be a local regulator of aldosterone production.

Diacylglycerol provides arachidonic acid for lipoxygenase products that mediate angiotensin II-induced aldosterone synthesis

The lipoxygenase products of arachidonic acid metabolism have been shown to be important mediators of stimulus secretion coupling in various endocrine tissues. We have recently shown that the 12-lipoxygenase product, 12-hydroxyeicosatetraenoic acid plays a key role as a new specific mediator of angiotensin II-induced aldosterone secretion in the adrenal. In view of the several pathways by which cellular arachidonate can be generated and the important role of diacylglycerol in angiotensin II-responses, we studied the role of diacylglycerol as the source of arachidonic acid for 12-hydroxyeicosatetraenoic formation. Treatment of normal human adrenal glomerulosa cells with the selective diacylglycerol-lipase inhibitor, RHC 80267, resulted in a dose-dependent inhibition of angiotensin II-induced aldosterone as well as 12-hydroxyeicosatetraenoic formation. These results suggest that AA derived from diacylglycerol is the precursor of 12-hydroxyeicosatetraenoic involved in angiotensin II-induced aldosterone secretion. These results reveal a new second messenger role for diacylglycerol in addition to activation of protein kinase C.

The reoxidation of cytochrome P-450 by paraquat inhibits aldosterone biosynthesis from 18-hydroxycorticosterone

Paraquat is an artificial electron carrier that captures electrons from reduced cytochrome P-450 instead of the natural acceptors, thus decreasing the concentration of reduced mitochondrial cytochrome P-450. In the present study, paraquat inhibited the biosynthesis of aldosterone from 18-hydroxycorticosterone by mitochondria from duck adult adrenal gland, under aerobic conditions. Since paraquat did not induce any change in the absorption spectrum of highly purified cytochrome P-450 11 beta, the possibility of a displacement of steroid by the drug is ruled out. Moreover, paraquat did not affect oxidative phosphorylating chain nor did it alter by itself the chemical structure of 18-hydroxycorticosterone. In our conditions, the inhibitory role of paraquat seems restricted to a capture of electrons from reduced cytochrome P-450. Under the same conditions metopirone and spironolactone, known to bind cytochrome P-450 11 beta at the steroid binding site, also inhibited the reaction. Altogether these results show that for aldosterone synthesis from 18-hydroxycorticosterone to take place, the steroid binding site on cytochrome P-450 must be accessible to 18-hydroxycorticosterone and that the cytochrome P-450 must be the direct donor of reducing equivalents. Hence, cytochrome P-450 appears as the final linking point between 18-hydroxycorticosterone and the reducing equivalents provided by NADPH.

Effect of angiotensin II and arginine vasopressin on aldosterone production and phosphoinositide turnover in rat adrenal glomerulosa cells: a comparative study

We have previously shown that arginine vasopressin (AVP) stimulates the production of aldosterone in isolated superfused adrenal glomerulosa cells by a mechanism that involves an increased turnover of phosphoinositides. In the present study we compared the characteristics of AVP- and angiotensin II (AII)-induced changes in phosphoinositide turnover and aldosterone production in the rat. Selected concentrations of the two peptides, which were equipotent in terms of the magnitude of changes induced in phosphoinositide turnover, stimulated aldosterone production to the same extent only in the initial phase of the stimulation. A sustained aldosterone response was only observed in AII-stimulated cells. On the other hand, the AVP-induced increase in incorporation of [32P]phosphate into phosphatidylinositol and the stimulation of inositol phosphate production were maintained during incubation. Preincubation of the cells with AVP failed to modify the effects of AII on phosphoinositide breakdown or aldosterone production. These results indicate that desensitization at the level of the receptor or at a post-receptor site is not responsible for the transient character of AVP-induced aldosterone production. Delayed activation of an inhibitory mechanism by AVP can also be excluded. Additivity of the stimulation of the phosphoinositide turnover observed at submaximally, but not maximally, effective concentrations of AII indicates that the two agonists act on the same phosphoinositide pool. We suggest that the sustained steroidogenic effect of AII involves an as yet unidentified mechanism, which is absent when the cells are stimulated with AVP.

Role of the lipoxygenase pathway in angiotensin II-mediated aldosterone biosynthesis in human adrenal glomerulosa cells

We studied the role of the lipoxygenase pathway of arachidonic acid metabolism in angiotensin II (AII)-stimulated aldosterone secretion in normal and adenomatous human adrenal glomerulosa tissue. In freshly isolated normal adrenal glomerulosa cells, the AII-mediated stimulation of aldosterone secretion was not altered by cyclooxygenase blockade with ibuprofen. In contrast, BW755c (10(-5) mol/L), a nonselective lipoxygenase inhibitor, and baicalein (10(-6) mol/L), a more selective 12-lipoxygenase blocker, inhibited AII-mediated aldosterone secretion, but did not alter basal aldosterone secretion. The glomerulosa cells produced the lipoxygenase products 12- and 15-hydroxyeicosatetraenoic acid (HETE) in the basal state, as measured by high pressure liquid chromatography and RIA. However, AII selectively stimulated only 12-HETE production [basal, 1329 +/- 207 (+/- SE) pg (3.99 +/- 0.62 pmol)/10(5) cells.h; AII, 2365 +/- 333 (7.09 +/- 1.0); n = 9; P less than 0.02], suggesting that 12-lipoxygenase activation may be involved in AII-mediated aldosterone secretion by normal cells. In addition, the lipoxygenase inhibitors that blocked AII-mediated aldosterone secretion also prevented AII-mediated 12-HETE formation. In contrast, neither ACTH nor K+ stimulated 12-HETE formation, suggesting that 12-lipoxygenase activation is primarily involved in AII action in normal glomerulosa cells. BW755c caused a marked dose-dependent inhibition of basal aldosterone secretion in freshly isolated cells from aldosterone-producing adenomas [APA; basal, 66 +/- 3 ng (182 +/- 8 pmol)/10(6) cells.h; 10(-5) mol/L BW755c, 49 +/- 2 (136 +/- 6); 10(-4) mol/L BW755c, 30 +/- 2 (83 +/- 6)]. In contrast, the cyclooxygenase inhibitor indomethacin and the selective 5-lipoxygenase inhibitor U60257 did not alter basal aldosterone secretion by these cells. The APA cells produced 12- and 15-HETE, and BW755c at the same dose that inhibited aldosterone secretion also inhibited the production of both 12- and 15-HETE. In the cultured APA cells, AII-stimulated aldosterone secretion was inhibited by BW755c [basal, 26 +/- 8 pg/mL (72.0 +/- 22.1 pmol/L); AII, 336 +/- 79 (930 +/- 218); AII plus BW755c, 92 +/- 38 (255 +/- 105) n = 13; P less than 0.01]. The lipoxygenase products 12- and 15-HETE restored the stimulatory effect of AII during inhibition by BW755c, indicating a role for these lipoxygenase pathways in AII-mediated aldosterone secretion in APA cells. These results suggest that the stimulatory effects of AII on aldosterone secretion are mediated by stimulation of the lipoxygenase pathway in human zona glomerulosa cells.

Porcine brain natriuretic peptide, another modulator of bovine adrenocortical steroidogenesis

Porcine brain natriuretic peptide (pBNP) significantly inhibited aldosterone production stimulated by an angiotensin II analog and ACTH-stimulated cortisol secretion, together with simultaneously increasing the formation of cGMP in dispersed bovine adrenocortical cells. Receptors for pBNP were identified in bovine adrenal gland using an in vitro receptor autoradiographic technique and studies of 125I-pBNP binding. In vitro receptor autoradiography demonstrated specific binding sites for 125I-pBNP in bovine adrenal cortex. Complete displacement of 125I-pBNP by unlabeled pBNP or human atrial natriuretic peptide (hANP) can take place at these sites. Analysis of 125I-pBNP binding to bovine adrenocortical membrane fractions showed that the adrenal cortex had high-affinity, low-capacity pBNP-binding sites, with a dissociation constant (Kd) of 2.32 +/- 0.33 x 10(-10) M (mean +/- SE) and a maximal binding capacity (Bmax) of 36.7 +/- 1.6 fmol/mg protein. Moreover, the specific binding sites for 125I-pBNP were completely displaced not only by unlabeled pBNP but also by unlabeled hANP. The hANP dose required for 50% inhibition of specific 125I-pBNP binding was almost identical to that for pBNP (IC50 values for hANP and pBNP: 8.5 x 10(-10) and 6.5 x 10(-10) M, respectively). These results suggest that pBNP exerts a suppressive effect on bovine adrenocortical steroidogenesis via a receptor which may be shared with ANP.

Effect of calcium-channel blockade on the aldosterone response to sodium depletion and potassium loading in man

Angiotensin II (Ang II) and potassium (K+) increase aldosterone (Aldo) production in vitro via Ca2+-dependent mechanisms. To determine the effects of Ca2+ antagonism in vivo, we examined the influence of nifedipine on the Aldo response to Na+ depletion and K+ loading in 11 healthy subjects. On the fifth day of a low-Na+/high-K+ diet (10 mmol Na+/100 mmol K+) the subjects were randomly given either nifedipine 30 mg po or placebo, and on the sixth day they received the alternative drug. KCl in 5% glucose was infused on days 5 and 6 from 10:00 to 12:00 AM (0.6 mmol/kg over 2 hours). Dexamethasone was given to suppress adrenal corticotrophic hormone. Plasma renin activity (PRA) and plasma Aldo were determined every 20 minutes. Nifedipine induced a rise in heart rate at 60 minutes but did not change blood pressure. During KCl/glucose infusions, plasma glucose increased significantly, but plasma K+ remained stable. PRA, but not baseline plasma Aldo, was stimulated by nifedipine. KCl provoked a significant and similar Aldo rise (P less than .01) under placebo and nifedipine. Baseline Aldo/PRA ratio was reduced under nifedipine when compared to placebo (P less than .01), whereas during KCl infusions this ratio was similarly elevated under placebo and nifedipine. We conclude that acute inhibition of slow Ca2+ channels does not interfere with K+-induced Aldo secretion in man, suggesting that adaptive mechanisms operate in vivo.

Effect of atrial natriuretic factor on corticosteroid production by perifused frog interrenal slices

In order to investigate a possible role of atrial natriuretic factor (ANF) in the control of corticosteroid biosynthesis in amphibians, we have examined the effect of synthetic ANF (Arg 101-Tyr 126) on perifused frog interrenal slices. ANF did not affect the spontaneous secretion of corticosterone and aldosterone. In contrast, ANF (10(-6) M) inhibited ACTH-and angiotensin II-stimulated corticosteroid production. ANF was more potent in suppressing aldosterone than corticosterone secretion. Immunocytochemical studies using a specific ANF antiserum revealed the presence of ANF-like immunoreactive fibers in the vicinity of interrenal cells. It is thus proposed that, in amphibians, both "hormonal" ANF secreted by myocytes and "neurohormonal" ANF delivered by peptidergic nerve terminals coursing among interrenal cells may partake in the regulation of corticosteroidogenesis.

Aldosterone biosynthesis in mitochondria of isolated zones of adrenal cortex

An assumption that the aldosterone-synthesizing enzyme exists only in zona glomerulosa cells apparently contradicts our recent findings that a purified bovine adrenocortical cytochrome P-45011 beta catalyzes the aldosterone formation and the enzyme exists in both zones of the adrenal cortex. To gain more insight into the zone specificity of aldosterone production, the aldosterone-synthesizing activity of mitochondria prepared from the isolated zones of adrenal cortex of various animal species was investigated. The intact mitochondria from the bovine or porcine zonae fasciculata-reticularis could not produce aldosterone whereas those from the zona glomerulosa produced it at a significant rate. When the mitochondria from the zonae fasciculata-reticularis were solubilized by the addition of cholate, they produced aldosterone from corticosterone at a rate comparable to that of those from the zona glomerulosa. The presence of specific factor(s) in the zonae fasciculata-reticularis mitochondria inhibiting expression of the aldosterone synthetic activity is discussed. The mitochondria of the rat zonae fasciculata-reticularis could hardly catalyze aldosterone synthesis under the detergent-solubilized conditions, whereas those of the zona glomerulosa could. Immunoblot analysis revealed that the mitochondria of the zonae fasciculata-reticularis contained a protein of Mr 51,000 which was immunocrossreactive with a monoclonal antibody directed against P-45011 beta, whereas those of the zona glomerulosa contained two immunocrossreactive proteins of Mr 51,000 and 49,000. These results suggest that in the case of rat adrenal cortex, a specific aldosterone-synthesizing enzyme exists in the zona glomerulosa.

Neuronal and paracrine regulation of adrenal steroidogenesis: interactions between acetylcholine, serotonin and vasoactive intestinal peptide (VIP) on corticosteroid production by frog interrenal tissue

The adrenocortical cells of frog interrenal (adrenal) tissue are controlled by multiple factors. Recently, we have shown that corticosteroidogenesis is stimulated by acetylcholine released from splanchnic nerve terminals as well as by serotonin and vasoactive intestinal peptide (VIP) which are both contained in chromaffin cells. Since these 3 putative neuroregulators are known to interact with each other on various target organs, we have investigated possible coordinate actions of acetylcholine, serotonin and VIP on adrenal steroid production, using a perifusion system technique for frog interrenal tissue. Simultaneous infusion of submaximal doses of VIP (10(-5) M) and acetylcholine (5 X 10(-5) M) induced stimulations of corticosteroids (corticosterone and aldosterone) which were strictly additive. When VIP (10(-5) M) and serotonin (5 X 10(-6) M) were infused together, a potentiation of the individual responses was observed. In contrast, concomitant infusion of acetylcholine (5 X 10(-5) M) and serotonin (5 X 10(-6) M) caused a total blockage of the stimulatory effect of serotonin. Muscarine (10(-5) M) caused a similar blockade of the response of adrenocortical cells to serotonin while nicotine (5 X 10(-5) M) did not alter the stimulatory effect of serotonin. The inhibitory effect of acetylcholine on serotonin-induced steroidogenesis was antagonized by atropine (10(-5) M). Thus, acetylcholine appears to block the corticotropic action of serotonin by interacting with typical muscarinic receptors. Taken together our results indicate that 3 of the neuroregulators which participate in the control of adrenal steroidogenesis, namely acetylcholine, serotonin and VIP, may interact on their target cell to modulate the activity of their congeners.(ABSTRACT TRUNCATED AT 250 WORDS)

Conversion of 11-deoxycorticosterone and corticosterone to aldosterone by cytochrome P-450 11 beta-/18-hydroxylase from porcine adrenal

Highly purified cytochrome P-450 11 beta-/18-hydroxylase and the electron carriers adrenodoxin and adrenodoxin reductase were prepared from porcine adrenal. When the enzyme was incubated with the electron carriers, 11-deoxycorticosterone (DOC) and NADPH, the following products were isolated and measured by HPLC: corticosterone, 18-hydroxy-11-deoxycorticosterone (18-hydroxyDOC), 18-hydroxycorticosterone and aldosterone. All of the DOC consumed by the enzyme can be accounted for by the formation of these four steroids. Aldosterone was identified by mass spectroscopy and by preparing [3H]aldosterone from [3H]corticosterone followed by recrystallization at constant specific activity after addition of authentic aldosterone. Corticosterone and 18-hydroxycorticosterone were also converted to aldosterone. Conversion of corticosterone and 18-hydroxycorticosterone to aldosterone required P-450, both electron carriers, NADPH and substrate. The reaction is inhibited by CO and metyrapone. Moreover, all three activities of the purified enzyme decline at the same rate when the enzyme is kept at room temperature for various periods of time and when the enzyme is treated with increasing concentrations of anti-11 beta-hydroxylase (IgG) before assay. It is concluded that cytochrome P-450 11 beta-/18-hydroxylase can convert DOC to aldosterone via corticosterone and 18-hydroxycorticosterone. The stoichiometry of this conversion was found to be 3 moles of NADPH, 3 moles of H+ and 3 moles of oxygen per mole of aldosterone produced.

Na+-H+ and Na+-Ca2+ exchange in glomerulosa cells: possible role in control of aldosterone production

Sodium uptake by rat adrenal glomerulosa cells was stimulated by intracellular acidosis evoked by Na+-propionate. This process was inhibited by 5-(N,N-hexamethylene) amiloride (HMA), a known inhibitor of the Na+-H+ exchange. These experiments demonstrate the existence of the Na+-H+ exchange in glomerulosa cells. Although amiloride inhibited the angiotensin II- and adrenocorticotropic hormone (ACTH)-induced aldosterone response, HMA, a more specific inhibitor of Na+-H+ exchange, failed to do that. 45Ca2+ influx and efflux were dependent on intra- and extracellular Na+ concentrations. Amiloride analogues, known to inhibit Na+-Ca2+ exchange, reduced basal 45Ca influx. Although we could not reveal the activation of Na+-Ca2+ exchange by angiotensin II, inhibitors of Na+-Ca2+ exchange also inhibited the angiotensin- and ACTH-induced aldosterone response of glomerulosa cells. Our results suggest that Na+-Ca2+ exchange supports the maintenance of basal Ca2+ level in the cytoplasma of glomerulosa cells, and amiloride derivatives inhibit aldosterone production by reducing Ca2+ level below resting values.

Further investigations on the atrial natriuretic factor (ANF)-induced inhibition of the growth and steroidogenic capacity of rat adrenal zona glomerulosa in vivo

A prolonged infusion with ANF (20 micrograms/kg/h for 7 days) induced atrophy of zona glomerulosa cells and lowering of basal plasma concentration of aldosterone in rats whose hypothalamo-hypophyseal-adrenal axis and renin-angiotensin system had been interrupted by the simultaneous administration of dexamethasone/captopril and maintenance doses of ACTH/angiotensin II. Chronic ANF treatment also caused comparable reductions in the aldosterone response of zona glomerulosa cells to the acute stimulation with angiotensin II, potassium and ACTH. These data are interpreted to indicate that ANF exerts an inhibitory effect on the growth and secretory activity of rat zona glomerulosa, and that the mechanism underlying this action of ANF does not involve blockade of renin release or ACTH secretion.

Simultaneous determination of intracellular free calcium and aldosterone production in bovine adrenal zona glomerulosa

Angiotensin II (AII) induces an initial rapid but transient rise in [Ca2+]i detected with aequorin in bovine adrenal capsule strips. The rise in [Ca2+]i begins immediately after AII addition, reaches a peak in 30 seconds, and returns to near basal values within 5 minutes. The [Ca2+]i transient is receptor-mediated and its height is dose-dependent. The increase in [Ca2+]i is largely due to the release of Ca2+ from an intracellular pool. The uncorrected peak rise in [Ca2+]i after 1 X 10(-6) M beta-[asp1]-AII stimulation is approximately 3 fold, from 110 nM to 300 nM; the peak rise, corrected for diffusion and nonsynchronous cellular response, is from 110 nM to 1.2 microM. Perifusion of aequorin-loaded strips with beta-[asp1]-AII, an aminopeptidase-resistant analog of AII, allows the simultaneous measurement of [Ca2+]i and aldosterone production rate. Levels of agonist which generate a transient rise in [Ca2+]i also produce a sustained increase in aldosterone production rate, but the two events are temporally separated: the transient rise in [Ca2+]i precedes the increase in aldosterone production rate. However, there is a strong correlation, r = 0.94, between the amplitude of the initial [Ca2+]i transient and the magnitude of the sustained increase in steroid production rate.

A case of glucocorticoid-suppressible hyperaldosteronism with aldosterone producing adenoma

A 34-yr-old woman with hypertension (142/102 mmHg), hypokalemia, high plasma and urinary aldosterone and low plasma renin activity was studied. A left adrenal tumor and enlarged right adrenal gland were demonstrated by adrenal venography. During administration of dexamethasone (2 mg daily, for 3 weeks), urinary aldosterone excretion decreased abruptly from 22.5 to 9-11 micrograms/day, serum potassium increased and blood pressure fell to 120-130/80-90 mmHg. After left adrenalectomy, all manifestations improved with no medication. The resected adrenal gland revealed clear cell adenoma and micronodular adrenocortical hyperplasia. The patient was considered to be a rare case of glucocorticoid-suppressible hyperaldosteronism with an aldosterone-producing adenoma.

Effects of opioid peptides on aldosterone production: stimulatory effect of leu-enkephalin

The effects of several opioid peptides (Leu-enkephalin, Met-enkephalin, D-Ala2,D-Leu5-enkephalin, and peptide E) on aldosterone secretion have been studied in isolated bovine adrenal glomerulosa cells. Leu-enkephalin significantly increased aldosterone production in a dose-dependent manner (10(-10)-10(-7) M). Similar results on steroidogenesis were obtained with the synthetic opioid D-Ala2,D-Leu5-enkephalin, whereas much higher concentrations of Met-enkephalin were required. Peptide E did not affect steroidogenesis. Naltrexone or naloxone (10(-5) M) potentiated the effect of Leu-enkephalin on aldosterone secretion. The effect of a general opioid antagonist (diprenorphine) or an agonist (etorphine) was also studied. The stimulation by Leu-enkephalin of aldosterone secretion was only partially blocked by diprenorphine. Etorphine (10(-6) and 10(-8) M) had no effect on basal steroidogenesis. It is proposed that the stimulatory effect of Leu-enkephalin on aldosterone production could be mediated by a different receptor than the classical opioid receptors presently known.

The use of cell permeabilization for studying the mechanisms of action of angiotensin II in the adrenal cortex and vascular smooth muscle

Some applications of the technique of electropermeabilization to the study of the mechanisms of action of angiotensin II in two of its physiological target cells, the adrenal zona glomerulosa and the vascular smooth muscle cell, are described. The technique proved useful for characterizing the second messenger role of inositol 1,4,5-trisphosphate, its metabolic pathways and the effect of Ca2+ on steroidogenesis.

In vitro studies in primary aldosteronism: baseline steroid production and aldosterone responses to ACTH and angiotensin II

The spontaneous glucocorticoid production in control adrenal cells (N = 10) and in the adenoma cells (N = 15) exhibited comparable geometric mean values: 1.896 nmol/ml/4-5 x 10(5) cells per 2 h (confidence limits: 0.428-8.391) and 1.852 nmol/ml (0.326-12.241), respectively. The same results were obtained for the three samples of nodular hyperplasia cells. When cortisol and corticosterone were measured separately, there was no significant difference between the outputs for control cells and those for pathological cells. Baseline aldosterone production in control cells showed a geometric mean of 2.525 pmol/ml (0.236-27.192). In the 15 adenomas, spontaneous production was extremely important: 57.297 pmol/ml (3.357-976.692). The difference was highly significant (P less than 0.0005). Aldosterone levels in the 3 samples of nodular hyperplasia cells were not different from the control values. In 9 out of the 15 adenomas, aldosterone responses to 10(-10) mol/l ACTH, expressed as stimulated/basal production, were above normal: 3.58 +/- 0.86 (SEM) against 1.48 +/- 0.08 (P less than 0.025). In the remaining 6 and in the 3 samples of nodular hyperplasia cells, there was a slight or no response. Angiotensin II (AII) stimulated both adenoma and nodular hyperplasia cells to varying degrees, without any obvious difference between these two categories. A combination of ACTH (10(-12) mol/l) and AII (10(-12) mol/l) had a synergistic action on aldosterone production in cells classed in the adenoma group. These findings demonstrate that despite the abnormal rate of aldosterone formation in adenoma cells, the production rate of corticosterone and cortisol remains normal. They unmask two functional categories with regard to ACTH in the adenoma group. Finally, they underline the relative insensitivity of nodular hyperplasia cells to ACTH.

Isolation and structure of corticostatin peptides from rabbit fetal and adult lung

A 34-amino acid peptide and three other structurally related peptides were isolated from rabbit fetal and adult lung. These cationic arginine- and cysteine-rich peptides inhibit corticotropin (ACTH)-stimulated rat adrenal cell corticosterone production. The peptide was called corticostatin (CSI). CSI was purified by reverse-phase HPLC and was shown to be homogenous from its amino acid analysis. Its sequence was determined on a gas-phase sequenator. The structure of CSI is Gly-Ile-Cys-Ala-Cys-Arg-Arg-Arg-Phe-Cys-Pro-Asn-Ser-Glu-Arg-Phe-Ser-Gly- Tyr-Cys - Arg-Val-Asn-Gly-Ala-Arg-Tyr-Val-Arg-Cys-Cys-Ser-Arg-Arg. CSI was found to markedly inhibit ACTH-stimulated corticosterone production by rat adrenal cells in vitro but did not affect basal levels. CSI did not affect the stimulation of aldosterone synthesis by angiotensin II in rat zona glomerulosa cells but it did suppress ACTH-stimulated aldosterone synthesis in whole adrenal cells, demonstrating that CSI is a specific inhibitor of ACTH-stimulated corticosteroid synthesis. The minimum effective concentration of CSI inhibiting ACTH-stimulated (33 pM) corticosterone production was 5 nM (20 ng/ml), the ED50 (50% effective dose) was 25 nM and steroidogenesis was completely inhibited at concentrations greater than 500 nM (2 micrograms/ml).

Reduced urinary aldosterone excretion rates with normal plasma concentrations of aldosterone in the very elderly

Although aldosterone production declines with age, so does the aldosterone metabolic clearance rate (MCR), and the net effect of age on the circulating level of aldosterone may be less than can be predicted from production rates alone. The effect of age on aldosterone production and plasma levels was studied in a group of elderly individuals at a very advanced age when susceptibility to the impacts of age might be particularly pronounced. Seventeen nursing home patients, ages 75-99 (mean age 86 years), had aldosterone production assessed from the urinary excretion rate of the acid hydrolyzable 18-glucuronide conjugate of aldosterone. Aldosterone excretion was low in the elderly when compared to a group of healthy, young to middle-aged subjects: 123 +/- 19 (SEM) vs. 234 +/- 18 ng/h (P less than 0.001). However, plasma aldosterone concentrations in the elderly were well within a range observed in much younger and fully ambulatory subjects: 14.1 +/- 1.3 in the elderly vs. 15.9 +/- 1.8 ng/dL in the young. The plasma aldosterone concentration was apparently maintained at a normal level by a coincident decrease in both the metabolic clearance rate and the aldosterone production rate. In conclusion, an aldosterone deficiency state resulting from an age-correlated reduction in aldosterone production is probably uncommon in the elderly.

Stimulation of chick adrenal steroidogenesis by avian parathyroid hormone

Dispersed chick adrenocortical cells were incubated with avian parathyroid hormone (aPTH) or ACTH. Accumulation of cyclic AMP (cAMP), activity of cAMP-dependent protein kinase and the secretion of corticosterone and aldosterone, in response to these hormones, were measured. Accumulation of cAMP and activity of cAMP-dependent protein kinase were stimulated by both aPTH and ACTH as well as by cholera toxin. Cyclic AMP production followed a similar time-course when stimulated by either peptide hormone. Stimulation of steroid hormone secretion was detectable after 20 min of incubation with ACTH, but only after 40 min with aPTH. The maximal steroid hormone secretion by adrenocortical cells was similar when induced by either peptide hormone. The aPTH concentrations needed for half-maximal response of corticosterone and aldosterone secretion were higher than those for ACTH (2.5- and 2-fold respectively), but still within the physiological range. The 11 beta-hydroxylase inhibitor metyrapone inhibited the secretion of both corticosterone and aldosterone when induced by either aPTH or ACTH. The results suggest that aPTH is almost as potent as ACTH in stimulating the secretion of corticosterone and aldosterone from chick adrenocortical cells and utilizes a cAMP-dependent pathway similar to that of ACTH.

Interrenal activity in the female lizard Lacerta vivipara J.: in vitro response to ACTH 1-39 and to [Sar1, Val5] angiotensin II (ANG II)

A perifusion system technique was developed in order to determine in vitro the respective roles of ACTH and ANG II in the regulation of adrenal steroidogenesis in the lizard Lacerta vivipara. Synthetic human ACTH 1-39, administered as 20-min pulses, stimulated corticosterone (B) and aldosterone (A) release in a dose-dependent manner. The increase in corticosterone output was higher than that in aldosterone output, leading to an enhancement of the B/A ratio. Iterative stimulations with 1 nM ACTH (20-min pulses every 120 min) led to reproducible increases in corticosterone and aldosterone release. Prolonged stimulation with 1 nM ACTH (up to 240 min) caused a sustained increase in corticosteroid release, suggesting that, in the lizard, ACTH does not induce any desensitization phenomenon. The angiotensin II analogue [Sar1, Val5] ANG II also stimulated corticosterone and aldosterone release in a dose-dependent manner; the stimulatory effects of ANG II on both steroids were very similar. These results indicate that, in lizards, ACTH plays a major role in the regulation of adrenal steroidogenesis. Since ANG II stimulates the production of gluco- and mineralocorticoids, our data raise the question of the existence of two cell types synthesizing corticosterone and aldosterone, respectively, in reptiles.

Verapamil directly inhibits aldosterone synthesis by adrenal mitochondria in vitro

The action of verapamil, a calcium channel blocker, on the last step of aldosterone biosynthesis (transformation of 18-hydroxycorticosterone into aldosterone) was studied using duck adrenal mitochondria in the absence of regulatory factors. Results show that 10(-5) M verapamil inhibits the transformation of 18-hydroxycorticosterone into aldosterone by 52.8%. Moreover, our findings show that verapamil induces only a slight inhibition of respiratory capacity without action on respiratory control and does not displace 18-hydroxycorticosterone from cytochrome P450 11 beta which catalyses the reaction. Thus, this study does not explain the mechanism of inhibition induced by verapamil on the last step of aldosterone synthesis but it is of interest to note, for clinical use, that this inhibition is not linked to regulatory factors of aldosterone production. Since primary hyperaldosteronisms are characterized by their independence vis-á-vis regulatory factors, administration of verapamil may be particularly interesting for treatment of primary hyperaldosteronisms.