Mechanisms of Inhibition of Aldosterone Secretion by Adrenocorticotropin

Abstract

The mechanisms by which prolonged administration of ACTH causes a decrease in aldosterone secretion were studied in the rat. After 6 days of treatment with ACTH (2 U/day), blood corticosterone was elevated and plasma aldosterone was decreased in rats maintained on either a normal or low sodium diet. PRA was also decreased, probably secondary to increased sodium and/or fluid retention. In collagenase-dispersed glomerulosa cells from adrenals of ACTH-treated rats, angiotensin II receptors were markedly decreased, as were the in vitro aldosterone responses to angiotensin II, ACTH, 8- bromo-cAMP, and potassium. However, the production of deoxycorticosterone and precursor steroids was increased, indicating the presence of a block in the late aldosterone biosynthetic pathway. Measurement of the activity of biosynthetic enzymes of the steroidogenic pathway in isolated mitochondria revealed an 80% increase in side-chain cleavage enzyme in both glomerulosa and fasciculata mitochondria from ACTH treated rats. Although ACTH injection also increased 11-hydroxylase activity in the fasciculata zone, this enzyme was reduced by 50% in capsular mitochondria. The 18-hydroxylase activity in adrenal capsular mitochondria was markedly decreased by ACTH treatment in both normal and sodium-restricted animals. The importance of ACTH-induced steroidogenesis in the development of altered glomerulosa cell function was indicated by the ability of aminoglutethimide to prevent the inhibitory effects of ACTH on angiotensin II receptors and PRA. It is likely that the observed inhibition of the renin-angiotensin system is responsible for the decrease in angiotensin II receptors and 18-hydroxylase, since both are highly dependent on the trophic effect of angiotensin II. The specific lesions produced in adrenal glomerulosa cells by long term ACTH treatment include decreased levels of angiotensin II receptors, 11-hydroxylase, and 18-hydroxylase. These changes are secondary to the suppression of renin-angiotensin activity and are res onsible for the impaired aldosterone secretion that results from prolonged treatment with ACTH. {Endocrinology108: 522, 1981)