Prolonged ACTH infusion suppresses aldosterone secretion in spite of high renin activity

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Abstract
Five normal young males on a low Na diet received i.v. ACTH (1-24) infusions (10 IU/24 h) for 100 h in addition to diuretics. The aim of the study was to find out whether the biphasic effect of ACTH on aldosterone (initial stimulation followed by escape) could be prevented by keeping plasma renin activity (PRA) at a fairly constant high level. PRA was .apprx. 20 ng/kg per min before and towards the end of the ACTH infusion. Plasma aldosterone and aldosterone excretion rates were only transiently stimulated, but the first was relatively more suppressed than the latter at the end of the ACTH infusion. Plasma 18-OH-corticosterone followed the same pattern. Even on the last infusion day, aldosterone and 18-OH-corticosterone levels were still higher than in normal ambulatory Na-replete men. The fasciculata steroids cortisol, 11-deoxycorticosterone and corticosterone were continuously stimulated by ACTH. The biphasic response of zona glomerulosa steroids to ACTH is basically independent of renin and angiotensin II. However, the marked suppression of aldosterone secretion observed in Na replete individuals during prolonged ACTH treatment was not seen. Angiotensin II or a different factor associated with Na depletion may partly protect the zona glomerulosa from adverse effects of ACTH observed in the Na-replete state.

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