Steroid profiles formed by rat adrenocortical whole tissue and cell suspensions under different conditions of stimulation

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.

Control of aldosterone secretion in zona glomerulosa cell suspensions and in the perfused adrenal gland of the rat

The secretion of aldosterone and its responses to stimulation have been studied in rat adrenal zona glomerulosa tissue incubated as intact capsules or as collagenase-dispersed cell suspensions, and in intact perfused rat adrenal glands. Several differences are apparent in the functions of the various preparations. Aldosterone secretion rates are similar in incubated intact capsules and in the perfused gland. Relative to corticosterone, lower yields of aldosterone are obtained in dispersed glomerulosa cell in vitro. This may be related to the loss in the dispersed cells of a pool of tissue steroid (aldosterone or a precursor) which is revealed only in intact tissue incubations by trypsin stimulation of aldosterone secretion. Trypsin-released aldosterone is increased by prior dietary sodium restriction. In addition, differences occur in the responses of dispersed cells and perfused glands to stimulation. Perfused glands from animals on a normal diet are less sensitive to stimulation by ACTH or alpha-MSH, but more sensitive than dispersed cells to angiotensin II amide. In the perfused gland, sensitivity of response (lowest effective concentration) to all three stimulants is increased by prior dietary sodium restriction, in contrast to dispersed cells in which increased sensitivity has been reported only to alpha-MSH. The perfused gland is particularly sensitive to angiotensin II amide, and a bolus administration of 1 amol gives significant stimulation in glands from animals on low sodium intake. Electrical (field) stimulation or dopamine administration at 10(-6) mol/l (which is ineffective in dispersed cells) both depress aldosterone secretion by the perfused gland. The data suggest that the sequestered pool of steroid is utilized in the perfused gland for aldosterone secretion. They furthermore suggest that in the intact gland there are mechanisms, which involve neural components, for intraglandular regulation of aldosterone secretion, which are lost in dispersed cells in vitro. Such mechanisms may be involved in sensitivity increases in sodium depletion.

Effects of protease inhibitors on adenylate cyclase activation and aldosterone production in rat adrenal zona glomerulosa cells

It has been shown that serine proteases are involved in aldosterone and 18-hydroxycorticosterone production by the rat adrenal zona glomerulosa in response to a variety of stimulants. From evidence presented for various tissues, including the rat adrenal cortex, the observation that adenylate cyclase can be activated by proteolytic enzymes and inhibited by protease inhibitors has led to the suggestion that serine proteases may also be involved in the hormonal stimulation of adenylate cyclase. In studies designed to test this hypothesis using protease inhibitors, only high concentrations (greater than 10(-4) M) of TAME (p-tosyl-L-arginine methyl ester) inhibited ACTH stimulated steroid and cAMP production in rat adrenal glomerulosa cells. TPCK (tosyl-L-phenylalanine chloromethylketone) and TLCK (tosyl-L-lysine chloromethylketone) were found to have a similar effect at very high concentrations (10(-2) M) but had no effect at the serine protease inhibitory concentration of 5 X 10(-6) M. Other protease inhibitors tested had no effect on ACTH-stimulated cAMP but the inhibitory effect of high concentrations of protease inhibitors on ACTH-stimulated adenylate cyclase was duplicated by the polyanion dextran sulphate. The results suggest that the inhibitors act through non-specific membrane effects and that proteases are not involved in the activation of zona glomerulosa adenylate cyclase by ACTH. In view of these findings it is concluded that a more rigorous approach should be applied to the use of protease inhibitors in whole cell systems, and that the concept of hormonal activation of adenylate cyclase via proteolytic events, which is based on studies with such inhibitors, should be reconsidered.

The relationship between tissue preparation and function; methods for the study of control of aldosterone secretion: a review

The study of the control of aldosterone synthesis and secretion by the rat adrenal gland has over the past thirty years involved the application of many different in vivo and in vitro techniques. In this review the relationship between the data that each of these methods has produced is compared. There are striking differences in overall steroid production rates, and in the qualitative nature of the steroid profile which the various methods produce. In particular, aldosterone is secreted at higher rates in vivo, and when whole tissue preparations are used in vitro, than in incubations of isolated glomerulosa cells. In addition, while corticosterone is a major product of glomerulosa tissue in vitro, the available evidence suggests that it is not a major glomerulosa product in vivo.

alpha-MSH analogues and adrenal zona glomerulosa function

Recent studies on the control of adrenal zona glomerulosa function and aldosterone secretion have focussed attention on the role of MSH-like peptides. In particular, at low concentrations, alpha-MSH has a specific stimulatory effect on rat adrenal glomerulosa cells. The synthesis of alpha-MSH analogues which have potent and prolonged effects on melanocyte systems offers new methods of examining the specificity of this response. Two peptides were tested in which potential for a beta-turn configuration was stabilised. These were: [Nle4, D-Phe7]-alpha-MSH and the cyclic [Cys4, Cys10]-alpha-MSH. In contrast to their effects on melanocyte systems, only [Cys4, Cys10]-alpha-MSH stimulated glomerulosa cells, and it was equipotent with alpha-MSH, while [Nle4, D-Phe7]-alpha-MSH and shorter fragments had no effect when added alone. [Nle4, D-Phe7]-alpha-MSH, however, augmented the response of cells already maximally stimulated with alpha-MSH and in this respect its actions resembled those of gamma-MSH and related peptides. The augmentation produced by [Nle4, D-Phe7]-alpha-MSH and gamma 3-MSH was not additive when the two peptides were added together with alpha-MSH. The results suggest that the specificity of the alpha-MSH receptors in rat adrenal glomerulosa cells and the peptide structure-function relationships in this system are different from those described for melanocytes.

alpha-MSH and zona glomerulosa function in the rat

The responses of rat adrenal zona glomerulosa cells to stimulation by alpha-MSH and ACTH and related peptides have been studied. The major findings were that: (1) alpha-MSH stimulated corticosterone production in glomerulosa cells from from normal animals at concentrations of about 10(-10) mol/l, but other steroids, including aldosterone, were not significantly stimulated until levels of 10(-7) mol/l were used. Peptide structure-function relationships showed that in the adrenal cortex, in contrast with other systems, ACTH 4-10 had no effect and did not block the response of glomerulosa cells to alpha-MSH, bisacetyl Ser 1-alpha-MSH, (nor-valine-12)-alpha-MSH, and ACTH 1-13 amide were equipotent with alpha-MSH, while alpha-MSH 1-10 had activity but was considerably less potent. alpha-MSH 6-13, 7-13, 8-13 and lys-11-acetyl-alpha-MSH were all inactive. N-formyl-N-epsilon-benzyloxycarbonyl alpha-MSH stimulated only at 10(-6) mol/l. (2) Normalised alpha-MSH dose-response curves for aldosterone production in glomerulosa cells from normal rats, and corticosterone in inner zone cells were coincident. In glomerulosa cells, prior sodium depletion shifts the dose-response curve for aldosterone to the left, indicating a more sensitive response, and for corticosterone to the right. Bromocriptine treatment (which depresses the level of alpha-MSH in circulating plasma) and metoclopramide (which enhances it) respectively increased and decreased the sensitivity of the response of corticosterone to alpha-MSH in subsequently incubated glomerulosa cells, but had no effect on aldosterone. (3) In contrast, normalised ACTH stimulated dose-response curves for glomerulosa corticosterone and aldosterone, and for fasciculata corticosterone production were all coincident, and were unaffected by sodium depletion, or by metoclopramide or bromocriptine pretreatment. (4) Cyclic-AMP production by glomerulosa cells was stimulated by alpha-MSH only at levels of in excess of 10(-5) mol/l, five orders of magnitude greater than required to produce significant corticosterone stimulation. Under cyclic-AMP stimulation, the normalised responses of glomerulosa corticosterone and aldosterone, and of inner zone corticosterone were all coincident. The data suggest that alpha-MSH at low concentrations (less than 10(-7) mol/l) interacts with a glomerulosa cell receptor which is distinct from the ACTH receptor but interacts with the ACTH receptor at concentrations greater than 10(-'5) mol/l. Corticosterone production is stimulated by alpha-MSH in cells from normal animals at concentrations within the normal range for circulating plasma (approximately 3 X 10(-10) mol/l), while aldosterone is stimulated by similar concentrations of alpha-MSH in cells from sodium depleted animals. The effects of sodium depletion are not modulated through changes in plasma alpha-MSH levels. At low concentrations alpha-MSH stimulation of glomerulosa cells is unlikely to be modulated by cyclic-AMP as second messenger.

Origins of the differences in function of rat adrenal zona glomerulosa cells incubated as intact tissue and as collagenase-prepared cell suspensions

While in vitro incubation of dispersed cell preparations of adrenal cell types has been widely used as an experimental model, few studies have addressed the possibility that the enzymic and mechanical treatments involved may affect tissue functions. Using rat adrenal whole capsule tissue, consisting of glomerulosa cells still attached to the connective tissue capsule together with some fasciculata cells, and dispersed glomerulosa cell preparations formed by a variety of enzymic and incubation treatments, striking differences have been demonstrated between the functions of the various preparations in vitro. Under ACTH stimulation, whole capsules produced (ng per pair +/- s.e.) 405 +/- 35 ng aldosterone, 650 +/- 60 ng 18-hydroxycorticosterone (18-OH-B) and 850 +/- 90 ng corticosterone. In cells dispersed by collagenase incubation followed by repeated pipetting and filtration, aldosterone and 18-OH-B yields under ACTH stimulation fell to values less than 10% of those produced by whole tissue, whereas corticosterone values were unchanged. Omitting the filtration step gave a less well marked decline in aldosterone and 18-OH-B to 50% of intact tissue values. When the tissue was not dispersed after collagenase incubation, aldosterone and 18-OH-B outputs were similar in the two preparations. The decline in aldosterone and 18-OH-B is not attributable to loss in cell-cell contact alone, since short term culture of collagenase dispersed cells on contracting collagen discs did not restore the capacity to produce these steroids, and a decline in their output also occurred in similar culture of intact capsule tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of steroids by in vitro superfusion from adrenals of the Mongolian gerbil (Meriones unguiculatus): effect of acute stress

1. The output of steroids by in vitro superfusion from adrenals of normal gerbils was studied; the glands secreted the following amounts of steroids (ng/animal/hr): 272 (glucocorticosteroids), 60 (aldosterone), 5.0 (progesterone), 1.0 (androstenedione) and 1.0 (testosterone). 2. Glucocorticosteroid and progesterone output from superfused glands of animals stressed by exposure to a novel environment (a) on concentrated ether vapor (b) was significantly higher than that of control animals (glucocorticosteroids: a: 3-9 min, b: 3-30 min after start of superfusion; progesterone: a, b: 3 min after start of superfusion). 3. Aldosterone output was not affected by the stressors applied. 4. Glucocorticosteroid plasma levels of 204 ng/ml were found in control animals. Exposure to a novel environment or concentrated ether vapor resulted in significantly elevated glucocorticosteroid concentrations (511 ng/ml and 760 ng/ml, respectively). 5. Neither testosterone nor progesterone plasma levels were changed by these stressors.

Effects of stimulation on the steroid profile formed by rat adrenal capsule tissue incubated in vitro

A characteristic of the response of non-dispersed rat adrenal capsule tissue (mainly zona glomerulosa) to ACTH stimulation is that corticosterone and aldosterone production is increased whereas 18-hydroxy-deoxycorticosterone (18-OH-DOC) is not. The effects of potential second messengers on the steroid profile were compared with those of ACTH and K+ ions in adrenal capsule incubations. ACTH stimulated corticosterone, 18-hydroxycorticosterone and aldosterone, but not 18-OH-DOC. In contrast, K+ (5.9 mM) stimulated 18-OH-DOC as well as the other capsule products. Compared with controls incubated with EDTA, the addition of Ca2+ and Mg2+ ions invariably stimulated aldosterone and 18-hydroxycorticosterone, while the effects on corticosterone were variable, and 18-OH-DOC production was unaltered. Addition of dibutyryl cyclic AMP (1 mM and 0.3 mM) or cyclic GMP (1mM) stimulated all products. The results show that Ca2+ ions and dibutyryl cAMP may have slightly different effects in that the cyclic nucleotides can stimulate all products whereas Ca2+ and Mg2+ ions preferentially support aldosterone and 18-hydroxycorticosterone. However, none of the potential intracellular stimulants studied fully reproduce the characteristic response of non-dispersed tissue to ACTH in which the secretion of corticosterone and 18-hydroxy-DOC is disassociated.

Dopaminergic control of aldosterone: modulation of the response of rat adrenal zona glomerulosa cells to alpha-Msh by pretreatment with bromocriptine or metoclopramide

Bromocriptine treatment in rats (3 mg/kg per day, 7 days) significantly reduced alpha-msh and aldosterone plasma levels 2 hrs after the final treatment in animals on low, normal and high sodium diets. Alpha-MSH dose response curves for corticosterone and 18-hydroxydeoxycorticosterone (18-OH-DOC) in subsequently incubated glomerulosa cells gave stimulation at lower concentrations of alpha-MSH (10(-10) moles per litre) than in cells from untreated animals (10(-9) moles per 1). Curves for aldosterone (ald) and 18-hydroxycorticosterone (18-OH-B) were also affected in cells from animals on a low sodium diet. Fasciculata-reticularis cell responses to ACTH were unaffected. Metoclopramide (4 mg/kg per day, 7 days) elevated plasma alpha-MSH, although ald was unaffected, but inhibited the glomerulosa cell response to alpha-MSH in vitro. Acute dopaminergic responses in plasma ald may be mediated through alpha-MSH in rats, but chronically alpha-MSH may down- regulate glomerulosa cell alpha-MSH receptors. It is unlikely that alpha-MSH mediates the adrenocortical response to sodium depletion.

Morphological correlates of hormone secretion in the rat adrenal cortex and the role of filopodia

Rat adrenals in different states of stimulation were examined by transmission electron microscopy following perfusion fixation using an in situ isolated-circulation technique. In unstimulated glands, intracortical capillaries were constricted and the cells of the cortex were pressed closely together with little development of filopodia or intercellular spaces. Glands fixed during the period of operative stress, or following a 1 hr perfusion with Adrenocorticotropic hormone (ACTH) showed that the radially orientated capillaries of the cortex were massively expanded, and the cells of both the glomerulosa and fasciculata exhibited an extensive development of filopodia on their surfaces. These filopodia extended into large intercellular spaces, where they often entered into complex relationships with filopodia from neighboring cells. The development of filopodia by cells of the adrenal cortex was also observed using scanning electron microscope techniques. In cells either incubated with ACTH in vitro or isolated from adrenals of rats treated with ACTH in vivo, the filopodia were numerous, often branched, and could reach as much as 1 micro m in length. In contrast, adrenal cells obtained from animals pretreated with cortisol were smooth surfaced. Other cell characteristics, including mitochondria, smooth endoplasmic reticulum, dense granules, and coated vesicles did not show such dramatic correlations with the state of stimulation. It is considered that the development of filopodia and intercellular space is related to secretory mechanisms in the rat adrenal cortex.

alpha-MSH at physiological concentrations stimulates "late pathway" steroid products in adrenal zona glomerulosa cells from sodium restricted rats

alpha-MSH stimulates steroid secretion by rat adrenal zona glomerulosa cells and tissues but not fasciculata/reticularis cells when added to in vitro incubations. With glomerulosa cells from control animals on a normal sodium intake, production of corticosterone was significantly stimulated at an alpha-MSH concentration of 10(-9) moles per 1, with ED50 at 10(-8) moles per 1. Other steroid products, including 18-hydroxycorticosterone (18-OH-B), 18-hydroxydeoxycorticosterone (18-OH-DOC) and aldosterone were only significantly stimulated at 10(-7) moles alpha-MSH per 1. In contrast, in cells taken from animals subjected to dietary sodium restriction, aldosterone and 18-OH-B were significantly stimulated at 10(10) moles alpha-MSH per 1, whereas corticosterone and 18-OH-DOC were unaffected at all concentrations tested. Circulating plasma levels of alpha-MSH in control animals were 2.5 +/- 0.4 x 10(-10) moles per 1, but were unchanged by dietary sodium restriction or by sodium loss induced by diuretic (LASIX) administration. However, the threshold concentration at which alpha-MSH induces increased aldosterone secretion in cells from sodium depleted rats clearly falls well within the physiological range, and it is therefore likely that alpha-MSH contributes to the support of aldosterone secretion in these animals in vivo.

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).