The Effects of Ouabain on Steroid Production by Rat Adrenal Cells Stimulated by Angiotensin II, αl–24 Adrenocorticotropin, and Potassium*

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Abstract
Aldosterone and corticosterone production by rat adrenal glomerulosa cells was significantly (P < 0.01) increased by the cardiac glycoside, ouabain octahydrate, at a concentration of 10-5 M. Concentrations greater or less had no effect. Ouabain had a biphasic effect when added to cells maximally stimulated by angiotensin II (2.4 .times. 10-8 M) and .alpha.1-24 ACTH (1.4 .times. 10-10 M); 10-5 M ouabain raised aldosterone output significantly above the already elevated levels (P < 0.05), while 10-3 M ouabain blocked stimulation of aldosterone production by angiotensin II or ACTH completely (P < 0.001). Ouabain at a dose of 10-4 M completely inhibited aldosterone output in response even to large doses of .alpha.1-24 ACTH (1.4 .times. 10-7 M) and significantly reduced glomerulosa cell responses to increasing doses of angiotensin II. Increasing extracellular K concentration caused a dose-dependent reversal of the 10-4 M ouabain block so that at the highest K doses used (13 and 18 meq/l), aldosterone and corticosterone production was equal to their output with K alone. Ouabain [10-4 M] did not significantly alter either threshold or maximum corticosterone output by fasciculata cells in response to ACTH. Ouabain does not have a nonspecific toxic effect on adrenal cells and modifies only glomerulosa and not fasciculata cell responsiveness to acute stimulation. Changes in intracellular K or K flux are important determinants of the steroidogenic response to acute stimulation of glomerulosa but not fasciculata cells. Studies assessing the role of intracellular K+ using a mixed population of adrenal cells and/or using only corticosterone as the index of steroidogenesis may give erroneous conclusions.
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