The Effects of Dexamethasone and Captopril on Plasma Aldosterone Response to Exogenous Angiotensin II in Normal Men

The response of plasma aldosterone to exogenous angiotensin II was evaluated in five normal volunteers on three occasions, once without endogenous ACTH or angiotensin II suppression (control), once with ACTH suppression (dexamethasone) and once with ACTH and angiotensin II suppression (dexamethasone and captopril). Plasma aldosterone concentration (PAC) fell from a control of 6.8 +/- 1.6 (mean +/- SEM) to 4.4 +/- 0.4 ng/dl with dexamethasone (p less than 0.05) and to 1.8 +/- 0.2 ng/dl with dexamethasone and captopril (p less than 0.001). PAC increased dose-dependently upon infusion rates of angiotensin II (0.2, 0.4, 0.8, 1.0, 1.2, 2.5 and 5.0 ng/kg/min) on each occasion, but aldosterone responsiveness to infused angiotensin II (change and percentage from base line levels) was not altered by the suppression of endogenous ACTH secretion with dexamethasone with each incremental infusion of the octapeptide. However, change in PAC caused by angiotensin II in the suppression of ACTH and angiotensin II was greater than that in the control at an infusion rate of 0.2 ng/kg/min (p less than 0.05), 1.2 ng/kg/min (p less than 0.05) and 2.5 ng/kg/min (p less than 0.01), and it was also greater than that in the suppression of ACTH at an infusion rate of 0.2 ng/kg/min (p less than 0.05) and 2.5 ng/kg/min (p less than 0.01). These results demonstrate that in normal men, base line aldosterone levels are controlled not only by the renin-angiotensin system, but also, in part, by ACTH. The aldosterone response to angiotensin II, however, does not depend upon endogenous ACTH secretion, an action of angiotensin II on the pituitary to release ACTH. Simultaneous administration of dexamethasone and captopril may be a useful tool to assess the sensitivity of aldosterone production in the adrenal glomerulosa with exogenous angiotensin II since endogenous ACTH and angiotensin II can be suppressed by these medications.