Regulation of aldosterone secretion during altered sodium intake

The interactions of the renin-angiotensin system with other factors in the regulation of aldosterone secretion were analyzed during altered sodium in the rat. During sodium restriction, the rise in aldosterone one secretion was accompanied by trophic changes in the adrenal glomerulosa zone including increased angiotensin II receptors and enzymes of early and late steps in the aldosterone biosynthetic pathway. All these effects of sodium restriction were reproduced by infusion of angiotensin II, and could be prevented by administration of the converting enzyme inhibitor, SQ 14,225. These findings indicate that the adrenal secretory and trophic responses to sodium restriction are mediated by angiotensin II. In hypophysectomized rats, the basal activities of the enzymes of the early aldosterone biosynthetic pathway were reduced, contributing to the blunted aldosterone responsiveness to sodium deficiency. However, sodium restriction for 6 days significantly increased adrenal glomerulosa angiotensin II receptors and enzymes of the early and late aldosterone biosynthetic pathway, indicating that the pituitary gland is not necessary for the adrenal effects of angiotensin II. In contrast to the prominent glomerulotropic actions of angiotensin II in rats on normal or low sodium intake, infusion of angiotensin II during high sodium intake did not increase blood aldosterone, angiotensin II receptors, or 18-hydroxylase activity, indicating that the trophic actions of the octapeptide are determined by the state of sodium balance. In recent studies, other factors including potassium, dopamine and somatostatin have been shown to potentiate or inhibit the actions of angiotensin II on the adrenal gland. The ability of such factors to influence the effects of angiotensin II could serve as a protective mechanism to modulate aldosterone responses to angiotensin II when elevations in the circulating level of the peptide occur in the absence of sodium deficiency.