ANGIOTENSIN-II ACTS VIA THE TYPE-1 RECEPTOR TO INHIBIT 17-ALPHA-HYDROXYLASE CYTOCHROME-P450 EXPRESSION IN OVINE ADRENOCORTICAL-CELLS

In this study we have investigated the effect of angiotensin-II (A-II) on cortisol production and 17-alpha-hydroxylase cytochrome P450 (P450(17-alpha)) expression in primary cultures of ovine adrenocortical cells and the A-II receptor subtypes that mediate these responses. While A-II alone had no stimulatory effect on cortisol secretion, it inhibited the cortisol response to ACTH (10(-8) M) in a dose-dependent manner (K(i), < 0.1 nM; maximum inhibition, 60-80%). While prolonged treatment with ACTH (10(-8) M) increased the expression of P450(17-alpha), cotreatment with A-II (10(-8) M) also inhibited ACTH-stimulated expression, as determined by changes in mRNA, immunoreactive P450(17-alpha), and 17-alpha-hydroxylase activity. A study of the effects of the AT1 and AT2 receptor antagonists, DuP 753 and PD 123319, on binding of [I-125]A-II to ovine adrenocortical cells showed that the A-II receptor population was predominantly of the AT1 subtype. The effects of A-II on inhibition of cortisol secretion in response to ACTH and the activation of phosphoinsitidase-C in response to A-II alone were both fully antagonized by DuP 753, but not by PD 123319. Furthermore, the inhibitory effects of A-II on expression of P450(17-alpha), as measured at the levels of mRNA, immunoreactive protein, and enzyme activity, were reversed by DuP 753 (10(-5) M), but not PD 123319 (10(-5) M). We conclude that A-II has a potentially important role in the control of cortisol secretion and long term maintenance of P450(17-alpha) expression in the ovine adrenal cortex, and that the effects of A-II on both cortisol secretion and P450(17-alpha), expression are mediated through the AT1 receptor, which is coupled to phosphoinositidase-C.