Regulation of adrenal steroidogenesis during chronic stress

The mechanism of the altered adrenal responsiveness during chronic stress was studied by analysis of ACTH and Ang II responses and the expression and activity of steroidogenic enzymes in the adrenal cortex of rats subjected to repeated immobilization (2 hr/day for 14 days), or repeated i.p. injection of 1.5 M NaCl. Concomitant with increased pregnenolone production and reduced aldosterone secretion by isolated adrenal glomerulosa cells of chronically stressed rats, P-450scc mRNA were increased and P-450aldo mRNA levels were decreased in adrenal zona glomerulosa. Consistent with elevated plasma corticosterone levels, isolated adrenal fasciculata cells from stressed rats showed higher cAMP, pregnenolone and corticosterone responses to ACTH. Adrenal fasciculata area and levels of P-450scc, but not those of P-450(11s) hydroxylase were significantly increased. The effects of repeated stress on adrenal steroidogenesis were mimicked by repeated ACTH injections. The half life of corticosterone in plasma measured with [3H]corticosterone was increased in stressed rats but not in ACTH injected rats. This study shows that chronic stress leads to a) inhibition of mineralocorticoid secretion due to inhibition of the late biosynthetic pathway, and b) increased circulating glucocorticoids due to increased ACTH receptor activity, expression and activity of the early pathway, and decreased glucocorticoid clearance. Altered adrenal glomerulosa and fasciculata function, but not changes in glucocorticoid clearance, are probably mediated by increased ACTH secretion during chronic stress.