Evidence that prolonged alpha-MSH infusion enhances the steroidogenic capacity of rat adrenal zona glomerulosa in vivo

Prolonged infusion with 120 micrograms/kg/day alpha-MSH significantly increased basal plasma level of aldosterone in the rat, as well as raised the acute aldosterone response to a bolus administration of a high dose of ACTH or angiotensin II. These findings suggest that chronic alpha-MSH treatment stimulates the steroidogenic capacity of rat zona glomerulosa.     

Effect of alpha-MSH on the corticosteroid production of isolated zona glomerulosa and zona fasciculata cells

α-MSH (10^?9 ? 6×10^?7M) potentiates the effect of ACTH (10^?11 ? 5×10^?9M) on adrenocortical steroidogenesis decreassng ED₅₀ of ACTH from 220 to 183 pg/ml on zona fasciculata corticosterone-, and from 739 to 437 pg/ml on zona glomerulosa aldosterone production. α-MSH alone increases aldosterone production of zona glomerulosa cells in doses (10^?9 ? 6×10^?7M) that do not stimulate zona fasciculata corticosterone production. The response of zona glomerulosa aldosterone production to α-MSH can be characterized by a bi-phase dose-response curve.     

Acute effects of alpha-MSH on the rat zona glomerulosa in vivo

alpha-MSH acutely enhanced the plasma concentration of aldosterone (but not that of corticosterone) in the rat, with a maximal response at a dose of 100 micrograms/kg. This dose of alpha-MSH increased the blood level o aldosterone and the activity of 11 beta-hydroxylase and 18-hydroxylase of capsular adrenals in rats infused for 24 h with dexamethasone, dexamethasone plus ACTH, or captopril plus angiotensin II, but not in animals treated with captopril alone. The plasma concentration of corticosterone and the activity of 11 beta-hydroxylase in the inner adrenal layers were not changed. These findings indicate that alpha-MSH is specifically involved in the acute stimulation of the late steps of the secretory activity of the rat zona glomerulosa, and that this action of alpha-MSH requires a normal level of circulating angiotensin II.     

Intramitochondrial bodies in sheep adrenal zona glomerulosa cells

Summary Relatively large, mostly rounded, very electron dense intramitochondrial bodies in adrenal zona glomerulosa cells of sheep are described and their nature and connection to protein in the mitochondria discussed. The so called azocarmine granules seen in the light microscope may be identical with the intramitochondrial bodies in the zona glomerulosa cells.     

Ascorbate stimulates monooxygenase-dependent steroidogenesis in adrenal zona glomerulosa

It is well known that ascorbic acid (Asc) is highly concentrated in the adrenal gland, but its function in the gland is not thoroughly elucidated. We therefore examined the possibility that Asc participates in steroidogenic monooxygenase systems of the adrenal cortex with the aid of the regenerating system including outer mitochondrial membrane cytochrome b (OMb). When Asc availability was limited in rat mutants unable to synthesize Asc, the increase in plasma aldosterone concentration under Na-deficiency was suppressed without effect on plasma corticosterone concentration. Aldosterone formation in the isolated mitochondrial fraction of the zona glomerulosa (zG) of the adrenal cortex was stimulated by the addition of Asc and NADH, while corticosterone formation was not. Consistently zG showed a high level of Asc regeneration activity and was rich in OMb among adrenocortical zones. Taken together, the enhanced aldosterone formation that is catalyzed by one of the steroidogenic monooxygenases, P450aldo, may be supported by Asc with its regenerating system.     

Isolation of bovine adrenal cortex mitochondria from the zona glomerulosa

Isolation procedures for the bovine adrenal cortex mitochondria from the zona glomerulosa are described. Special care was taken to avoid contamination of the mitochondria from the zona fasciculata.     

Steroidogenesis in the zona glomerulosa of the adrenal cortex I. Isolation and some properties of mitochondria from the zona glomerulosa of the bovine adrenal cortex

Isolation procedures for mitochondria from the zona glomerulosa of the bovine adrenal cortex are described and the properties of the mitochondria thus prepared are compared with those isolated from the zona fasciculoreticularis. The cristal membranes of mitochondria in the zona glomerulosa in situ are tubular or tubulovesicular, whereas those of mitochondria in the zona fasciculoreticularis in situ are vesicular. When mitochondria are isolated from the former zone, they invariably showed the condensed configuration regardless of isolation media, whereas those isolated from the latter zone in an ST medium showed the orthodox configuration. When Ca²⁺ was added to mitochondria isolated either from the zona glomerulosa or the zona fasciculoreticularis in an STE medium in the condensed configuration, a transition from the condensed to the orthodox configuration took place; the cristal membranes of mitochondria from the zona glomerulosa became tubular or tubulovesicular and those of mitochondria from the zona fasciculoreticularis became vesicular. Contaminations of mitrochondria of the zona glomerulosa with other cellular organelles were examined using various marker enzymes. There was no difference in cytochrome content between mitochondria of the two zones specified above. The coupling efficiency of mitochondria of the zona glomerulosa was found to be remarkably effected by temperature during the isolation procedures. Effects of various substrates, isolation media, and bovine serum albumin on the coupling efficiency of mitochondria of the glomerulosa are also described.     

Steroidogenesis in the zona glomerulosa of the adrenal cortex II. Distribution of cytochrome P-450 in the zona glomerulosa of the bovine adrenal cortex

Microsomes were obtained from the zona glomerulosa of the bovine adrenal cortex. Contamination of microsomes with other cellular organelles was examined using various marker enzymes and the electron microscope. Distribution of cytochrome P-450 in the zona glomerulosa was studied using various fractions including microsomes, described above, and mitochondria. The amount of cytochrome P-450 in mitochondria and in microsomes was determined to be 0.73 and 0.32 nmol/mg protein, respectively. The CO difference spectrum was affected not only by the concentration of added deoxycholate but also by the incubation time after addition. Approximately 40–50% of cytochrome P-450 in the samples was converted to cytochrome P-420 within 20–30 sec of incubation with deoxycholate.The content of RNA, phospholipids, and cytochromeb ₅ in microsomes obtained from the zona glomerulosa is also evaluated in comparison to that in microsomes obtained from the zona fasciculoreticularis.     

Chronic hypoxia induced ultrastructural changes in the rat adrenal zona glomerulosa

The adrenal cortex plays an important role in adaptation to various forms of stress, including hypoxia. While physiological changes in the aldosterone metabolism during hypoxia have been extensively described, few studies have focused on the morphological changes in the adrenal glands under chronic hypoxia. We studied the ultrastructure of the zona glomerulosa of 6-month-old Wistar rats exposed to chronic normobaric hypoxia. Animals were divided into two groups: control (n=12) and hypoxic (n=12). In this latter group, the animals were kept at 7% O2 concentration after a gradual adaptation (21, 15, 12, 10, 8, 7 vol% O2). The duration of the study was 112 days. In comparison with normoxic rats, body weight and adrenal gland weight of hypoxic animals was significantly reduced by 18.5% (p=0.006) and 14.7% (p=0.001) respectively. The thickness of the zona glomerulosa decreased due to atrophy of cells. The main ultrastructural changes observed were: 1) a decrease in, or complete elimination of, lipid droplet content; 2) a marked increase in lysosome number; and 3) the presence of giant mitochondria. Our findings show that rats fail to adapt to severe chronic hypoxia. The ultrastructural changes in the zona glomerulosa found in the present study could reflect changes in the aldosterone pathway.     

Rat atrial natriuretic polypeptide stimulation of adrenal zona glomerulosa cell growth

Rat atrial natriuretic polypeptide (rANP) was found to stimulate [3H] thymidine incorporation into the DNA of bovine adrenal glomerulosa cells in a primary culture in a dose-dependent manner. The minimum effective dose was a very low concentration (10(-12) M of ANP), suggesting that ANP had a physiological effect. These findings are the first indication that ANP possesses growth-stimulating activity with regard to adrenal zona glomerulosa cells.     

Structure-activity studies with ACTH/alpha-MSH fragments on corticosteroid secretion of isolated zona glomerulosa and fasciculata cells

The steroidogenic action of ACTH/alpha-MSH fragments was studied on isolated zona glomerulosa and zona fasciculata cells dispersed by collagenase. ACTH-(4-7), ACTH-(6-10), ACTH-(4-10) and ACTH-(11-13) stimulated corticosterone production of the zona fasciculata and aldosterone production of the zona glomerulosa cells. ACTH-(7-10) was ineffective. ACTH-(4-7) appeared to be the most potent peptide of the tested fragments. None of the fragments affected the steroidogenic action of ACTH-(1-39). It is suggested that similar to the melanotropic effect of alpha-MSH two 'message' sequences for adrenocortical stimulation exist in the alpha-MSH part of the ACTH molecule.     

Effects of IGF-I on proliferation and steroidogenesis of cultured adrenal zona glomerulosa cells

In a primary culture of bovine adrenal zona glomerulosa cells, insulin-like growth factor I (IGF-I)/somatomedin C stimulated DNA synthesis, as measured by [3H] thymidine uptake, at concentrations of 10(-9) and 10(-7) M. IGF-I also prevented ACTH-induced suppression of [3H] thymidine uptake. IGF-I in no way affected aldosterone secretion during short-term exposure to cultured cells, however. Our findings suggest that IGF-I plays an important role in the proliferation of adrenal zona glomerulosa cells.     

Serotonin stimulates calcium influx in isolated rat adrenal zona glomerulosa cells.

To investigate the role of calcium as a second messenger in serotonin-stimulated aldosterone secretion, radiolabelled calcium influx studies were carried out in purified rat adrenal zona glomerulosa cells using 45CaCl2. The results show that serotonin caused calcium influx within 45 seconds of addition and this continued for up to 105 seconds. Angiotensin II also caused calcium influx; however, the effect was significantly smaller than that of serotonin. Serotonin-stimulated calcium influx could be inhibited by the calcium antagonist verapamil and by methysergide, a selective serotonin receptor type-1/2 antagonist. The data indicate that serotonin directly stimulates calcium uptake in zona glomerulosa cells via calcium channels which are coupled to specific serotonin receptors.     

Dopamine inhibition of potassium-stimulated aldosterone biosynthesis in bovine adrenal zona glomerulosa cells

Dopamine inhibits angiotensin II-stimulated aldosterone production by an effect on the late phase of biosynthesis. This study was undertaken to investigate the effect of dopamine on potassium-stimulated aldosterone biosynthesis in adrenal glomerulosa cells in vitro. As potassium concentrations were increased from 0 to 12 mM, aldosterone production increased up to 6 mM potassium, but not beyond this concentration. Dopamine (10(-5)M) inhibited the aldosterone response to potassium. The effect of potassium on pregnenolone accumulation (the early phase of aldosterone biosynthesis) was assessed in cells treated with trilostane which inhibits the conversion of pregnenolone onward to aldosterone. Increasing potassium concentrations up to 12 mM gave increasing pregnenolone accumulation; however dopamine did not influence this effect. The potassium stimulated conversion of corticosterone to aldosterone, an index of activity in the late phase of aldosterone biosynthesis, was assessed using aminoglutethimide to prevent cholesterol side-chain cleavage. Significantly more corticosterone was converted to aldosterone at 6 mM potassium than at 0 or 12 mM; dopamine inhibited the conversion of corticosterone to aldosterone at 6 mM potassium. These data indicate that dopamine inhibits potassium-stimulated aldosterone production by an effect restricted to the late phase of the aldosterone biosynthetic pathway similar to its previously established effect on angiotensin II-stimulated aldosterone biosynthesis.     

Effect of a water-rich diet on adrenal zona glomerulosa in Gerbillus tarabuli

The objective of this work is to evaluate the aldosterone level and to study the gerbil adrenal zona glomerulosa morphology in the presence of an important water diet content during seven days. Thirty adult gerbils, Gerbilus tarabuli, were randomly assigned to two watering regimes, with fifteen gerbils per group. The first group was the control and the second group was exposed to a water-rich diet during seven days. Thin sections of the adrenal glands were observed in photonic and electron microscopy. Their blood was sampled and analyzed for aldosterone, electrolyte concentrations and hematocrit. Urine was collected after 24hours. A water-rich diet decreased the body weight but increased the hematocrit, total protein, aldosterone concentration and urine volume. In electronic microscopy, the adrenal zona glomerulosa cells present a decrease in lipid compartment and Golgi apparatus zone development. The blood electrolyte concentrations were not changed significantly. These findings indicate that the water-rich diet exerts a potent stimulatory effect on aldosterone secretion by the gerbil adrenal zona glomerulosa through plasma volume perturbation.