Effect of protein kinase inhibitors on ACTH-stimulated aldosterone production in rat zona glomerulosa cells

In order to obtain further evidence for the involvement of protein kinases in the short-term ACTH-stimulated aldosterone synthesis in rat zona glomerulosa cells, the effects of three different compounds with protein kinase inhibitory properties were investigated. Staurosporine, H-7 and trifluoperazine inhibited ACTH-stimulated aldosterone release in a dose-dependent manner. While the inhibitory effect of H-7 was reversible upon washing of the cells with inhibitor-free medium, the inhibition was maintained in cells treated with staurosporine or trifluoperazine. In contrast to the stimulated production, basal release of aldosterone even at the highest drug concentrations tested was not completely inhibited. We thus conclude that protein kinases may play a crucial role in short-term ACTH-stimulated aldosterone production in rat glomerulosa cells.

Endothelin-1 potentiation of angiotensin II stimulation of aldosterone production

Endothelin-1 (ET-1) binds to specific receptors in cultured bovine adrenal glomerulosa cells and stimulates aldosterone secretion with a 50% effective concentration (EC50) of 300 +/- 80 pM (mean +/- SE). The relative stimulatory potency for ET-1 is significantly less than that of angiotensin II (ANG II). The incubation of calf zona glomerulosa cells in primary culture with ET-1 and ANG II resulted in a significant potentiation of ANG II effect on aldosterone secretion. The EC50 of ET-1 potentiation of ANG II-induced stimulation of aldosterone secretion was 40 +/- 5 pM (mean +/- SE, n = 4), which is lower than the EC50 for ET-1 stimulation of aldosterone secretion. Adrenocorticotropic hormone (ACTH) stimulation of aldosterone secretion, but not that of potassium, was also potentiated by ET-1, but to a lesser degree. ET-1 and ET-1-mediated potentiation of ANG II-stimulated aldosterone biosynthesis increased both the early and late pathways of aldosterone biosynthesis, but the potentiation was greater for the early pathway. Preincubation with ET-1 for at least 15 min, followed by extensive washing to remove bound ET-1, also resulted in persistent potentiation of ANG II-mediated aldosterone secretion. ET-2, sarafotoxin, and vasoactive intestinal contractor potentiation of ANG II action were very similar to that of ET-1. ET-3 and Big-ET-1 potentiated ANG II stimulation only at the highest doses tested and the proendothelin-(110-130) fragment was inactive. ET-1 potentiation of ANG II action is likely to be mediated through an ETB receptor subtype.(ABSTRACT TRUNCATED AT 250 WORDS)

Are adrenal catecholamines involved in the enhancement of aldosterone production in cold acclimated rats?

In order to determine the possible role of adrenal catecholamines in the enhancement of aldosterone production in cold acclimated rats, dopamine (DA), noradrenaline (NA) and adrenaline (A) contents of adrenals were investigated in cold acclimated (or not), hypophysectomized (or not) rats. The DA content, DA being an inhibitor of aldosterone synthesis, increased in hypophysectomized rats and remained unchanged in sham-operated ones following cold exposure. The NA and A contents, these being, in vitro, stimulators of aldosterone production did not increase, in either group of cold acclimated rats. It is concluded that adrenal catecholamines do not seem to be implicated in the enhancement of aldosterone production.

Effects of angiotensin subtype 1 and subtype 2 receptor antagonists in normotensive versus hypertensive rats

The purpose of this study was to examine in vivo the importance of angiotensin subtype 1 (AT1) versus subtype 2 (AT2) receptors in spontaneously hypertensive (hypertensive) versus normotensive Wistar-Kyoto (control) rats. Intravenous infusions of DuP 753, a selective AT1 receptor antagonist, abolished the pressor responses to intravenous infusions of angiotensin II in both strains, and the potency of DuP 753 in this regard was similar in the two strains. DuP 753 also abolished angiotensin II-induced aldosterone release in both strains; however, with respect to inhibiting angiotensin II-induced aldosterone release, DuP 753 was more potent in hypertensive compared with control rats. In hypertensive but not control rats, DuP 753 inhibited angiotensin II-induced aldosterone release at doses lower than required to inhibit angiotensin II-induced pressor responses. Intramesenteric infusions of DuP 753 abolished mesenteric vascular responses to intramesenteric infusions of angiotensin II with a similar potency in both strains. In control but not hypertensive rats, angiotensin II consistently potentiated noradrenergic neurotransmission in the mesenteric vascular bed, and this effect of angiotensin II was abolished by DuP 753. High doses of PD123177, a selective AT2 antagonist, did not influence any of the aforementioned effects of angiotensin II in either strain.(ABSTRACT TRUNCATED AT 250 WORDS)

[Role of prostaglandin E1 in steroidogenesis by isolated rat adrenal cells]

In order to investigate the effects of prostaglandin E1 (PGE1) used in hypotensive anesthesia on the adrenal endocrine function, aldosterone, corticosterone (Comp B) and cAMP production were measured in isolated glomerulosa (G-c) and fasciculata cells (F-c) of the rats. Rat glomerulosa and fasciculata cells were obtained by enzymatic digestion of the adrenals of male wistar rats. The cell pellet was suspended in Hank's balanced salt solution containing 0.1% BSA and distributed in 900 microliters aliquots to polyethylene tubes. The samples were preincubated for 90 min in a 37 degrees C water bath aerated with 5% CO2/95% O2. PGE1 or ACTH 50 microliters was added and incubated for 4 hr. Total volume of the incubation medium is 1.0 ml. Aldosterone and cAMP were measured by radioimmunoassay and Comp B was determined by fluorimetric method. PGE1 increased significantly the basal secretion of aldosterone and Comp B in G-c and F-c, respectively. The steroidogenic effect of PGE1 was dose dependent in aldosterone production. This aldosterone production was also accompanied with cAMP production. On the other hand, significant increase of cAMP was not observed in comp B production. These results suggest that cAMP may be the second messenger in PGE1-induced aldosterone production in G-c. But PGE1 receptors in F-c seem not to be coupled to the adenylate cyclase system. The addition of ACTH and PGE1 resulted in inhibition of aldosterone secretion when compared with that obtained by ACTH alone. Several researchers have shown that low doses of PGE1 depressed the basal aldosterone secretion. These findings may be contributing to Na-uresis effect during PGE1-induced hypotension.

[Organ transplantation. One of the biochemical reasons for the race against the clock]

The authors have studied the subcellular functioning of human adrenal glands removed from subjects in a stage IV coma. The present study has a two-fold interest: on the one hand, it offers biochemical information on a key element in the intermediate metabolism (namely, the mitochondrial energetic metabolism, occurring in a fragile tissue which, under a state of shock, is primarily affected; the results obtained on such type of tissue may therefore be inferred to other organs); on the other hand, it allows a wider approach of the adrenal biochemical mechanisms during a stage IV coma. The mitochondrial fraction was obtained by differential centrifugation carried out immediately after organ removal. The steroid synthesis, studied using radioactive precursors, turned out to be similar to that found in other mammals. Respiratory characteristics, determined by polarography with a Clark oxygen electrode, at 37 degrees C, were satisfactory: respiratory intensity was 77.25 +/- 12.16 nanomoles O2/min/mg mitochondrial protein in the presence of succinate 15 mM and respiratory control was 1.93 +/- 0.15 in the presence of ADP 37 microM. The respiratory chain functioned in a classical manner: rotenone 25 microM did not inhibit respiration in the presence of succinate 15 mM, while it did with L-malate 15 mM. In the presence of succinate 15 mM, the respiratory intensity was inhibited at 87.4 percent and 76.7 percent by KCN 0.01 microM and antimycin A 0.09 microM respectively; with DNP 85 microM, it was multiplied by 5. However, the value of the P/O ratio was low (0.24 +/- 0.04). Under the present conditions, this may highlight the difficulty to synthetize ATP whenever neither the functioning nor the regulation of the multi-enzymatic complex accounting for oxygen consumption are affected. This result clearly confirms that the shortest possible delay between organ removal and transplantation is crucial, as the renewal of cell structures requires energy. These fundamental research studies account for the major concerns of reanimation teams. This also raises the issue of the role of fundamental researchers within a transplant surgery team.

Inhibition of aldosterone biosynthesis by 18-ethynyl-deoxycorticosterone

The inhibiting effects of 18-ethynyl-deoxycorticosterone (18-E-DOC) as a mechanism-based inhibitor on the late steps of aldosterone biosynthetic pathway were examined in calf adrenal zona glomerulosa cells placed in the primary culture. Baseline and ACTH (10(-9) M)-, angiotensin-II (10(-8) M)-, and potassium (12 mM)-stimulated production of aldosterone and 18-hydroxycorticosterone were inhibited in a dose- and time-dependent manner. At 1 microM, 18-E-DOC produced a 73% inhibition, and at 10 microM, it produced a 94.6% inhibition of aldosterone secretion. Preincubation with 10 microM 18-E-DOC for 5 min followed by washing resulted in 75% inhibition of aldosterone secretion. The maximal degree of inhibition was reached after 60 min of preincubation. The degree of the inhibition of 18-hydroxycorticosterone production was almost same as that of aldosterone. Preincubation with 10 microM 18-E-DOC for 60 min, followed by extensive washing and reincubation with medium for 24 h, resulted in recovery to more than half the production of the control cells. Minimal changes occurred in the production of corticosterone (slight increase), 18-hydroxydeoxycorticosterone (slight increase) in zona glomerulosa cells, and cortisol (no changes) in zona fasciculata cells. These studies show that 18-E-DOC is a specific inhibitor of the late pathway of aldosterone biosynthesis. 18-E-DOC could be valuable as a therapeutic agent in those conditions associated with increased aldosterone production where a specific inhibitor would be useful.

Angiotensin II receptor and postreceptor events in adrenal glomerulosa cells from streptozotocin-induced diabetic rats with hypoaldosteronism

Streptozotocin-induced chronic diabetic rats develop hyporeninemic hypoaldosteronism. The hypoaldosteronism is associated with selective unresponsiveness of aldosterone to angiotensin II (AII) and an atrophy of the zona glomerulosa. To assess the nature of the adrenal unresponsiveness to AII, we examined the [125I]monoiodoAII binding and the responses of pregnenolone formation and aldosterone production to AII using adrenal glomerulosa cells from diabetic rats 6 weeks after an injection of streptozotocin. Comparisons were made using the cells from control rats treated with vehicle. Diabetic rats had low levels of plasma renin activity, plasma 18-hydroxycorticosterone, and plasma aldosterone, and normal levels of plasma corticosterone and plasma potassium. The zona glomerulosa width was narrower in diabetic than in control rats. Scatchard analysis of the AII binding data demonstrated that the number and affinity of the receptors were similar in the cells from control and diabetic rats. When corrected to an uniform number of cells per group, baseline levels of pregnenolone formation and aldosterone production were similar in the cells from control and diabetic rats. However, cells from diabetic rats had a less sensitive and lower response of both pregnenolone formation and aldosterone production to AII. In contrast, the effect of ACTH on pregnenolone formation and aldosterone production was similar in the cells from control and diabetic rats. These results indicate that the main defect responsible for the hypoaldosteronism may be located on some step(s) mediating between AII receptors and conversion of cholesterol to pregnenolone, presumably on the calcium messenger system, with a disturbance downstream from AII binding.

The biosynthesis of aldosterone

The cellular mechanisms for aldosterone biosynthesis are incompletely understood. Although the enzymes involved are now well characterized, the dynamics of aldosterone secretion in a variety of rat adrenal preparations are not consistent with the concept that freshly synthesized corticosterone is an important intermediate. In whole glomerulosa tissue preparations, aldosterone is more readily formed from endogenous precursors than from an added radioactive precursor, such as [3H]pregnenolone, and in the in situ perfused gland preparation, aldosterone responses to stimulation, for example by ACTH, are significantly more rapid than those of corticosterone, suggesting a tissue source of steroid substrate for aldosterone production other than corticosterone. The only steroid which is stored in rat adrenal glomerulosa tissue to any extent is 18-hydroxydeoxycorticosterone (18-OH-DOC), and this pool has been located in plasma membrane fractions. It is lost on preparation of collagenase dispersed glomerulosa cells. Since dispersed glomerulosa cell preparations produce significantly less aldosterone, relative to corticosterone, than incubated intact whole glomerulosa, it is plausible that this tissue pool (which is not found in the inner zones) is the immediate precursor for aldosterone formation. Further evidence shows that trypsin, which stimulates aldosterone (and 18-hydroxycorticosterone) production in rat intact glomerulosa tissue, but not in dispersed cells, stimulates translocation of protein kinase C to the plasma membrane. It is plausible that one function of protein kinase C in the rat adrenal zona glomerulosa is to mobilize membrane sequestered 18-OH-DOC for conversion to aldosterone.

The product of the CYP11B2 gene is required for aldosterone biosynthesis in the human adrenal cortex

The steroid 11 beta-hydroxylase (P450c11) enzyme is responsible for the conversion of 11-deoxycortisol to cortisol in the zona fasciculata of the adrenal cortex. Animal studies have suggested that this enzyme or a closely related isozyme is also responsible for the successive 11 beta- and 18-hydroxylation and 18-oxidation of deoxycorticosterone required for aldosterone synthesis in the zona glomerulosa. There are two distinct 11 beta-hydroxylase genes in man, CYP11B1 and CYP11B2, which are predicted to encode proteins with 93% amino acid identity. We used a sensitive assay based on the polymerase chain reaction to analyze the expression of the CYP11B1 and B2 genes. Transcripts of CYP11B1 were detected at high levels in surgical specimens of normal adrenals and also in an aldosterone-secreting adrenal tumor. Transcripts of CYP11B2 were found at low levels in normal adrenals, but at a much higher level in the aldosterone-secreting tumor. CYP11B2 mRNA levels were increased in cultured zona glomerulosa cells by physiological levels of angiotensin-II. The entire coding regions of both CYP11B1 and B2 cDNAs were cloned from the tumor mRNA. Expression of these cDNAs in cultured COS-1 cells demonstrated that the CYP11B1 product could only 11 beta-hydroxylate 11-deoxycortisol or deoxycorticosterone, whereas the CYP11B2 product could also 18-hydroxylate cortisol or corticosterone. A small amount of aldosterone was synthesized from deoxycorticosterone only in cells expressing CYP11B2 cDNA. These data demonstrate that the product of CYP11B2 is required for the final steps in the synthesis of aldosterone.

Inhibition of aldosterone production by pinacidil in vitro

Pinacidil, an antihypertensive agent that opens potassium channels, lowers plasma aldosterone levels in hypertensive patients by an unknown mechanism. In the present study, pinacidil's direct effects on production of aldosterone were assessed using isolated cells from bovine adrenal glomerulosa. Pinacidil was found to inhibit aldosterone production, both basally and during stimulation with either potassium, angiotensin II (Ang II), or adrenocorticotropic hormone (p less than 0.001), with half maximal inhibition occurring at 10(-5) M. As assessed by the exclusion of trypan blue from cells, pinacidil did not inhibit secretion through injurious effects on glomerulosa cells. Also, washing of cells previously exposed to pinacidil restored secretory responsiveness. Pinacidil did not alter cytosolic calcium (Ca2+) concentrations when aequorin was used as a photoluminescent indicator of Ca2+ levels, suggesting that pinacidil acted by a non-Ca(2+)-mediated mechanism. Consistent with direct inhibition of the late pathway in steroidogenesis was that pinacidil decreased conversion of pregnenolone and corticosterone to aldosterone. Pinacidil did not block binding of Ang II to its receptor, nor did it appear to affect adrenocorticotropic hormone-receptor binding, since stimulation by cyclic AMP, the post-receptor second messenger of adrenocorticotropic hormone, was also inhibited. In summary, pinacidil inhibited directly the adrenal's production of aldosterone. The mechanism whereby the inhibition occurred was unclear.

Interference of C17-spirosteroids with late steps of aldosterone biosynthesis. Structure-activity studies

Structure-activity relationships concerning the steroidal skeleton as well as the C21,17-ring systems could be established while investigating the inhibitory effects of 27 different C17-spirosteroids on aldosterone synthesis in vitro. 18-hydroxylation appeared to be the crucial point of interference with all active compounds, whereas impairment of 11 beta- and 21-hydroxylase, respectively, was of minor importance, i.e. occurring to a smaller degree and only with a few test substances. Inhibition of 18-hydroxylation was associated with the following structural features: C21,17-spiro-gamma-lactone ring with 17 beta-O-atom; 3-oxo group in combination with delta 4,5-6,7-diene structure or, alternately, combination of 3-oxo group or even a bulky 3-O-function, if it protrudes out of ring plane in beta-position, and 7a-thioalkyl- or thioacyl- or thiol groups; combination of 17-spiro-gamma-lactone and a 3-O-function may result in an active compound even without 7a-substituents, provided there are no additional groups fixed on the steroidal skeleton. Elimination of an angular methyl group (----nor-compound), however, is acceptable. On the other hand, inhibitory potency is abolished or diminished by the following structural features: 7a-groups containing oxidized sulphur (e.g. suphoxy- or sulphonyl groups); bulky 3-substituents fixed in the ring plane via double bond; 18-alkyl groups; 6 beta-substituents; 2-substituents in absence of 7a-groups, depending on their configuration (e.g. cycle or chain); introduction of a heteroatom at C21, i.e. instead of the carbonyl-C-atom. Mespirenone (CAS 87952-98-5), the test substance of central concern, possesses favourable structural features finding its expression in a correspondingly enhanced inhibitory action.

Inhibitory effects of the novel anti-aldosterone compound mespirenone on adrenocortical steroidogenesis in vitro

Mespirenone (CAS 87952-98-5), the delta 1,2-15 beta, 16 beta-methylene derivative of spironolactone, proved to be a potent and quite specific inhibitor of adrenocortical mineralocorticoid synthesis in vitro. At 10(-4) mol/l concentrations, the production of aldosterone as well as its possible precursor 18-OH-corticosterone was inhibited more than 40% (p less than 0.01), whereas corticosterone was elevated highly significantly. This points to a clearcut blockade of 18-hydroxylase on the main pathway of aldosterone synthesis by mespirenone. Decrease of 18-OH-progesterone- and increase of 21-deoxyaldosterone secretion suggests two additional points of interference on an alternate pathway of aldosterone biosynthesis, i.e. 18- and 21-hydroxylation, respectively. Thus, mespirenone causes an effective all-around inhibition of mineralocorticoid synthesis in rat adrenals. On the contrary, androstendione levels remained virtually unchanged indicating that mespirenone exerts no inhibitory effects on androgen synthesis. In conclusion, mespirenone, due to inhibition of mineralocorticoid synthesis in addition to antagonistic effects on the receptor level, is a candidate for the development of a new, potent and specific anti-aldosterone drug.

Angiotensin II receptor subtypes and biological responses in the adrenal cortex and medulla

Angiotensin II (AII) receptor subtypes and their potential coupling mechanisms were studied using recently developed peptide and nonpeptide antagonists in rat and bovine adrenal zona glomerulosa cells, as well as in membranes prepared from rat and bovine adrenal cortex and medulla. Comparison of the potencies of these novel antagonists to displace 125I-[Sar1,Ile8]AII from its binding sites revealed two distinct AII binding sites in membranes prepared from rat adrenal capsules (zona glomerulosa) and from rat adrenal inner zones containing the medulla. About 85% of the binding sites of the glomerulosa zone and 30% of those of the inner zones were of the AT1 subtype, with relative affinities for the nonpeptide antagonists Dup 753 and PD 123177 and the peptide antagonist CGP 42112A in the order of Dup 753 much greater than CGP 42112A greater than PD 123177. In contrast, the relative binding potencies for the other (AT2) population of binding sites were CGP 42112A greater than PD 123177 much greater than Dup 753. Neither AII nor its peptide antagonist [Sar1,Ile8]AII could distinguish between the two sets of binding sites. The effects of the new antagonists on functional responses of rat adrenal glomerulosa cells demonstrated that both AII-stimulated aldosterone production and the AII-induced inhibition of adrenocorticotropic hormone-stimulated cAMP formation were mediated by the AT1 receptor subtype. In bovine adrenals, only AT1 receptors were detected in membranes prepared from the cortex and the medulla, as well as in cultured glomerulosa cells. The relative inhibitory potency of Dup 753 was lower by an order of magnitude at bovine than at rat AT1 receptors. The inhibition of AII-induced aldosterone production by the various antagonists was closely correlated with their inhibitory potencies on 125I-[Sar1,Ile8]AII binding to bovine glomerulosa cells. These data suggest that the known effects of AII in adrenal glomerulosa cells are mediated through the AT1 receptor subtype and that the distribution and/or specificity of the AT2 receptors shows marked species variations.

Contrasting effects of sn-1,2-dioctanoyl glycerol as compared to other protein kinase C activators in adrenal glomerulosa cells

Angiotensin II acts on adrenal glomerulosa cells to induce the phospholipase C-mediated generation of inositol trisphosphate and sn-1,2-diacylglycerol as the major products of inositol phospholipid breakdown. This last product is known to activate protein kinase C, but its role in the action of angiotensin II on steroidogenesis has not been defined. We report herein that, in bovine adrenal glomerulosa cells, protein kinase C activators, such as phorbol 12,13-dibutyrate, 12-O-tetradecanoylphorbol-13-acetate, mezerein and sn 1,2 oleoyl acetoylglycerol, each failed to increase steroidogenesis. These results contrast with our recent report on the enhancement of aldosterone output by sn-1,2-dioctanoylglycerol (DiC8) [J. Steroid Biochem. 35 (1990) 19-33]. In addition, the difference between DiC8 and the other protein kinase activators was also observed in the pattern of 86Rb efflux from preloaded glomerulosa cells; only DiC8 mimicked the effect of angiotensin II on ion fluxes. Furthermore, staurosporine, a potent inhibitor of protein kinase C, was capable of amplifying the aldosterone output induced by a maximally effective concentration of DiC8 or angiotensin II. These data suggest that the effect of the cell permeant DiC8 on aldosterone biosynthesis either is not mediated by protein kinase C activation, or is mediated by a phorbol ester-insensitive isoenzyme of protein kinase C.

Benzamide derivatives provide evidence for the involvement of a 5-HT4 receptor type in the mechanism of action of serotonin in frog adrenocortical cells

We have previously shown that serotonin (5-HT) is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells and we have demonstrated that the action of 5-HT is not mediated by the classical 5-HT receptor subtypes i.e. 5-HT1, 5-HT2 and 5-HT3. Recently, a non-classical 5-HT receptor (termed 5-HT4) has been characterized using 4-amino-5-chloro-2-methoxy-benzamide derivatives as serotonergic agonists. In the present report, we have investigated the possible involvement of the 5-HT4 receptor subtype in the mechanism of action of 5-HT on steroid secretion. Increasing concentrations of benzamide derivatives (zacopride, cisapride and BRL 24924) gave rise to a dose-related stimulation of corticosteroid production, zacopride being the most potent compound of this series to enhance steroidogenesis. Prolonged administration (230 min) of zacopride induced a rapid increase in corticosterone and aldosterone output followed by a gradual decline of corticosteroid secretion. During prolonged exposure of adrenal tissue to zacopride (10(-5) M), the corticotropic activity of 5-HT (10(-6) M) was totally abolished. The stimulatory effects of 5-HT and zacopride were abolished by the non-selective 5-HT3 antagonist ICS 205 930. In contrast methysergide, a 5-HT1 receptor antagonist, and MDL 72222, a selective 5-HT3 antagonist did not block zacopride-induced corticosteroid secretion. Both 5-HT and zacopride induced a dose-related increase in cAMP production by frog adrenal slices. Taken together, these results indicate that the stimulatory effect of 5-HT on frog adrenocortical tissue is mediated by activation of a 5-HT4 receptor subtype positively coupled to adenylate cyclase.

17 alpha-hydroxylation deficiency

Cases of sexual immaturity and male pseudohermaphroditism due to disorders such as androgen resistance, 5 alpha-reductase deficiency, cholesterol desmolase deficiency, 3 beta-hydroxysteroid dehydrogenase deficiency, and testicular and ovary dysgenesis can easily be distinguished from 17 alpha-OHD. None of these disturbances result in hypertension. In the only other form of juvenile hypertension due to congenital adrenal hyperplasia, 11 beta-OHD, androgen excess leads to female pseudohermaphroditism and precocious puberty in the male patient. Patients with dexamethasone-suppressible hyperaldosteronism present with no sexual abnormalities. A diagnosis of 17 alpha-OHD can be readily assumed in the female patient with primary amenorrhea, hypertension, and hypokalemia. The absence of aldosterone, a measurement that is readily available, establishes this diagnosis even without the measurement of DOC.

Diagnosis of hyperaldosteronism

Hyperaldosteronism is associated with hypertension, potassium depletion, and suppressed plasma renin activity. It may involve one or both adrenal glands. This article reviews the different types of hyperaldosteronism and the diagnosis and management of each.

Dantrolene inhibits adrenal steroidogenesis by a mechanism independent of effects on stored calcium release

The muscle relaxant dantrolene has been widely used in signal transduction studies as an inhibitor of intracellular calcium release. However, in vivo studies have shown that the drug may inhibit steroidogenesis by a mechanism which is distinct from its effects on calcium mobilization. Using freshly isolated cells and mitochondria from the outermost regions of bovine adrenal cortex we have shown that dantrolene (0.2 mM) significantly inhibits steroid synthesis stimulated by either angiotensin II (AII) or by addition of various precursors. Our results suggest that dantrolene inhibits the rate-limiting steps of adrenocortical steroidogenesis, i.e. the intramitochondrial conversion of cholesterol to pregnenolone (for both aldosterone and cortisol) and the conversion of corticosterone to aldosterone (for aldosterone), by a mechanism independent from its known effects on calcium release. A possible alternative mechanism may involve direct inhibition of cytochrome P450-dependent hydroxylation reactions.

Stimulation of steroidogenesis by forskolin in rat adrenal zona glomerulosa cell preparations

The actions of forskolin have been investigated to determine to what extent its effects on steroidogenesis in rat adrenal preparations are dependent on activation of adenylate cyclase. In zona glomerulosa preparations, stimulation of both aldosterone and corticosterone production was obtained at concentrations of forskolin between 1 and 10 mumol/l. The effects of 10 mumol forskolin/l were additive with those of low doses (1 pmol/l) of corticotrophin (ACTH), but not with those of high doses (1 nmol/l) of ACTH. In contrast, in zona fasciculata/reticularis cells, doses of forskolin up to 10 mumol/l produced no significant stimulation of corticosterone production either alone or in the presence of ACTH (1 pmol/l and 1 nmol/l). The response to 1 nmol ACTH/l was attenuated in the presence of forskolin (10 mumol/l) in both zona glomerulosa and zona fasciculata/reticularis cell preparations. Cyclic AMP production increased progressively with dose up to 100 mumol forskolin/l in zona glomerulosa cells, whereas corticosterone production was maximal between 10 and 30 mumol forskolin/l and decreased at 100 mumol forskolin/l. In zona fasciculata/reticularis cells, cyclic AMP production was also increased by forskolin (1 and 10 mumol/l). The stimulation of zona glomerulosa steroidogenesis by forskolin (1-10 mumol/l) and ACTH (1-100 pmol/l) were both reduced by the adenylate cyclase inhibitor, N6-phenylisopropyladenosine (100 mumol/l). The calcium channel inhibitor, nifedipine, only reduced the steroidogenic response to forskolin (3 mumol/l) at doses of 300 mumol/l whereas the response to 8.4 mmol K+/l was inhibited at 10 mumol nifedipine/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Sites of action of angiotensin II, atrial natriuretic factor and guanabenz, on aldosterone biosynthesis

It is well known that atrial natriuretic factor (ANF) inhibits aldosterone biosynthesis. Recent studies showed that amiloride can also inhibit adrenal steroidogenesis. Since the antihypertensive agent, guanabenz, is structurally related to amiloride, we have examined its action on aldosterone biosynthesis. The aim of this work was to localize the sites of action of angiotensin II (AII) and of ANF on steroidogenesis and to compare the effects of guanabenz to ANF. Trilostane, an inhibitor of 3 beta-hydroxysteroid dehydrogenase was used to separately study the early and late pathways of aldosterone biosynthesis. The different steps of steroidogenesis are stimulated by AII. ANF inhibits the formation of pregnenolone, the steps between progesterone and deoxycorticosterone, deoxycorticosterone and corticosterone and finally, corticosterone and aldosterone with ED50 of 114 +/- 17, 199 +/- 90, 14 +/- 3 and 92 +/- 34 pM of ANF, respectively, and around 70% of inhibition. These steps are also inhibited by guanabenz with ED50 of 66 +/- 17 microM for the formation of pregnenolone, 1.6 +/- 1.3, 3.3 +/- 1.7 and 29 +/- 4 microM for the last 3 steps. The percentage of inhibition by guanabenz was at least 80% for all the steps except for progesterone to deoxycorticosterone which is less than 35%. These results indicate that the major site of action of both AII and ANF could be at the level of intracellular signal transduction for the activation of mitochondrial steroidogenic enzymes or for the transport of steroids to mitochondria. We also showed that guanabenz mimics the inhibitory effects of ANF. This study with guanabenz suggests that it might be a prototype for a new family of antihypertensive agents.

Histological and biochemical distinctiveness of atypical aldosterone-producing adenomas responsive to upright posture and angiotensin

Fifteen patients with primary aldosteronism were classified as angiotensin II-unresponsive aldosterone-producing adenoma (AII-U APA, n = 9), or angiotensin II-responsive aldosterone-producing adenoma (AII-R APA, n = 6), based on the responsiveness of aldosterone to upright posture and to angiotensin II infusion. Lack of aldosterone response to angiotensin II infusion immediately postoperatively in the AII-R APA subtype was consistent with previous responsiveness residing solely within the adenoma. Cortisol levels in five of the six patients with AII-R APA failed to suppress normally with dexamethasone consistent with some autonomous production of cortisol by the adenoma. In contrast, cortisol levels suppressed normally during dexamethasone administration in all patients with AII-U APA. This biochemical distinction can be added to the previously described overproduction of 18-oxo cortisol in AII-U APA but not in AII-R APA. Histological examination of adenoma sections revealed predominantly (greater than or equal to 50%) zona fasciculata type cells in AII-U APA. In contrast, AII-R APA contained less than 20% zona fasciculata type. Thus, biochemical differences between AII-U APA and AII-R APA subtypes of primary aldosteronism may be due to underlying differences in cellular composition of the aldosterone-producing adenomas.

Thapsigargin-induced increase in cytoplasmic Ca2+ concentration and aldosterone production in rat adrenal glomerulosa cells: interaction with potassium and angiotensin-II

Thapsigargin (Tg), a microsomal Ca2+ pump inhibitor, dose-dependently increases the cytoplasmic Ca2+ concentration and aldosterone production without having any striking effect on the formation of inositol phosphates in isolated rat adrenal glomerulosa cells. The interaction of Tg with the major Ca2(+)-mediated stimuli of glomerulosa cells on aldosterone production was also examined. The effects of Tg and the Ca2(+)-mobilizing angiotensin-II (AII) were additive. The aldosterone production stimulatory effect of potassium, which induces Ca2+ influx via voltage-operated Ca2+ channels, was potentiated by Tg. The positive interaction between Tg and potassium on aldosterone production raises the possibility that stimuli generating Ca2+ signal by depleting intracellular Ca2+ stores, such as Tg or AII, enhance the response of the cell to depolarization. Such an interaction between AII and potassium may have an important role in the physiological control of aldosterone production.