Directβ-Adrenergic Stimulation of Aldosterone Secretion in Cultured Bovine Adrenal Subcapsular Cells*

Primary culture of bovine adrenal subcapsular cells was used to investigate direct effects of catecholamines on aldosterone secretion. Cells dispersed with collagenase and DNAse and cultured at high density (1.5-2 million/ml) for 3 days displayed high sensitivity to angiotensin II and ACTH, with an ED50 of 1.4 and 1.5 nM, respectively. Adrenergic agonists elicited a 4- to 6-fold stimulation of aldosterone secretion with potency order (-)isoproterenol greater than (-)epinephrine equals (-)norepinephrine greater than (+)isoproterenol, and corresponding ED50 5, 240, 213, and 3000 nM, respectively. No reproducible inhibition by dopamine of basal or stimulated levels of aldosterone secretion could be detected, but a weak stimulatory effect was sometimes observed at high concentration greater than 10 microM. (-)Isoproterenol stimulation of aldosterone production was potently inhibited by the beta-adrenergic antagonists (-)alprenolol and (+)alprenolol with potencies of 1.8 and 110 nM, respectively. The alpha-adrenergic antagonists prazosin, yohimbine, and phentolamine only weakly inhibited (-)isoproterenol stimulation with potencies of 5, 13, and 140 microM, respectively. The potent beta 2-adrenergic antagonist ICI 118.551 and the weaker beta 1-adrenergic antagonist atenolol were roughly equipotent with potencies of 0.27 and 0.44 microM, respectively. Addition of the phosphodiesterase inhibitor Ro 20-1724 at 10 microM doubled the maximum stimulation effect of (-)isoproterenol without changing the potency of the catecholamine or the basal level of aldosterone secretion, suggesting a potential role of cAMP as a mediator of isoproterenol stimulation. These results indicate the presence of a beta 1-adrenergic receptor stimulating aldosterone secretion in bovine zona glomerulosa cells. The physiological significance of direct beta-adrenergic stimulation of aldosterone production is currently being assessed.