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

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 × 10-8 M) and αl–24 ACTH (1.4 × 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 αl–24 ACTH (1.4 × 10-7 M) and significantly reduced glomerulosa cell responses to increasing doses of angiotensin II. In contrast, increasing extracellular potassium concentration caused a dose-dependent reversal of the 10-4 M ouabain block so that at the highest potassium doses used (13 and 18 meq/liter), aldosterone and corticosterone production was equal to their output with potassium alone. On the other hand, 10-4 M ouabain did not significantly alter either threshold or maximum corticosterone output by fasciculata cells in response to ACTH. We conclude that in the doses used in this study, ouabain 1) does not have a nonspecific toxic effect on adrenal cells and 2) modifies only glomerulosa and not fasciculata cell responsiveness to acute stimulation. Thus, these data support the hypothesis that changes in intracellular potassium or potassium flux are important determinants of the steroidogenic response to acute stimulation of glomerulosa but not fasciculata cells. It also suggests that 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.