The biosynthesis of adrenal steroids: effects of angiotensin II, adrenocorticotropin, and potassium.

Abstract

The search for the physiologic mechanism controlling the biosynthesis of aldosterone has centered upon three factors-ACTH, the renin-angiotensin 1 system, and potassium. All three have been shown to stimulate the production of aldosterone in the intact animal (1-4). Despite a large number of in vivo experiments involving ,the rat, dog, sheep, and man, the exact locus of each stimulus within the control mechanism and the precise relationships of one to the other have not been clearly defined. In particular, disagreement persists as to the physiologic role of the renin-angiotensin system (2,3,5).The initial results of in vitro studies of the effects of ACTH and angiotensin on the biosynthesis of adrenal steroids have been published (6). In those studies, in which the effects upon aldosterone and cortisol were nonselective, relatively large amounts of both agents were used. Additional in vitro experiments have therefore been performed, studying the effects of smaller amounts of these agents as well as potassium, alone and in combination, in an attempt to elucidate further their role in the control of aldosterone biosynthesis. 1 Unless otherwise stated, the term "angiotensin" is used to designate the active octapeptide, angiotensin II. MethodsTissue preparation and incubation. The studies were carried out with slices of beef adrenal cortex prepared in the manner of the previous study (6). The glands were incubated within 2 hours after death of the animals. Slices were taken with a microtome.In studies upon aldosterone synthesis alone, only outer slices were incubated, since histologically this slice includes most of the zona glomerulosa. When cortisol synthesis was also studied, the next inner slice was also taken, since it includes considerable zona fasciculata. When only cortisol synthesis was studied, only the third slice was used. The different slices were shown to vary in their initial steroid content by assays of nonincubated slices used in four separate experiments. The mean steroid contents (in l'g per g tissue) were as, follows: 1) outer slices, aldosterone 3.85; corticosterone 3.65; cortisol 0.68; 2) second slices, aldosterone 3.03; corticosterone 5.55; cortisol 7.80; 3) third slices, aldosterone 0.15; corticosterone 2.36; cortisol 7.23. The slices used in each experiment were combined and minced to obtain uniformity. At least four vessels containing 400 to 667 mg of tissue were incubated and analyzed separately for each portion of each experiment.No effect of angiotensin upon this in vitro preparation was observed if the tissues were not first preincubated and the preincubation media replaced with fresh media. Therefore, in all experiments, the tissues were preincubated for 1 hour in Krebs-Ringer bicarbonate medium containing glucose at a concentration of 200 mg per 100 ml. The glucose was omitted in the studies of phosphorylase activity. The preincubation medium was then replaced with 5 ml of fresh medium and the appropriate stimulatory agent added. Each vessel was gassed with 95% 02-5% C02 and capped ti...

Site of stimulation of aldosterone biosynthesis by angiotensin and potassium

“…These findings are in accord with results of in vitro experiments (23)(24)(25) suggesting that the site of action of angiotensin and potassium is early in the aldosterone biosynthetic pathway, probably before the formation of pregnenolone. At what point in the steroidogenic pathway the various stimuli converge to produce their common effect of accelerating the formation of DOC remains to be determined.…”

The Syndrome of Congenital Adrenocortical Unresponsiveness to ACTH. Report of Six Cases

“…The addition of 3',5'-adenosine monophosphate produced no change in cortisol production, but did produce a marked increase in corticosterone. Outer slices (mainly glomerulosa) of beef adrenals have been shown to increase output of aldosterone and corticosterone when 3',5'-adenosine monophosphate is added to the incubation media [13]. In our experiments, the increase in corticosterone can therefore be considered as a direct effect of 3',5'-adenosine monophosphate on the zona glomerulosa.…”

Comparative Effects of Angiotensin and ACTH on Cyclic AMP and Steroidogenesis in Isolated Bovine Adrenal Cells

“…Thus far, the stimulation of cortisol synthesis by angiotensin has been reported in only two species (6)(7)(8)(9). It seems likely that the ability to synthesize cortisol in response to angiotensin is species specific since the human adrenal does not produce cortisol in response to angiotensin infusion (25,26).…”

“…Angiotensin has been shown to induce aldosterone synthesis in man (3,4) and in sheep with adrenal transplants (5), and to stimulate cortisol as well as aldosterone synthesis in isolated bovine adrenals (6,7) and in the hypophysectomized dog (8,9). However, attempts to demonstrate an effect of angiotensin on adrenal adenylate cyclase activity (10,11) or cyclic AMP levels (12) have thus far been unsuccessful.…”