PLASMA-ALDOSTERONE RESPONSE TO ACTH IN SUBTYPES OF PRIMARY ALDOSTERONISM

1. Aldosterone responsiveness to ACTH was compared in eleven patients with angiotensin-unresponsive (AII-U) aldosterone-producing adenomas ( APA), 16 with AII-responsive (AII-R) APA and 19 with bilateral adrenal hyperplasia (BAH). 2. After overnight recumbency, aldosterone levels were highest in AII-U APA and lowest in BAH. Following 2 h of upright posture, however, levels were similar among the three groups. 3. Durin g ACTH infusion, aldosterone levels in AII-U and AII-R APA were simila r, and higher than those in BAH. Because of the higher basal level, th e percentage rise in aldosterone was lower in AII-U APA compared with the other groups, as was the ratio of per cent aldosterone rise to per cent cortisol rise. 4. Slightly but significantly reduced plasma cort isol levels observed in the AII-R APA group may reflect secretion by A II-R APA of a cortisol-like substance that is capable of suppressing A CTH and thus adrenal cortisol production. 5. The tendency of aldostero ne to follow the diurnal rhythm of ACTH in AII-U APA may thus represen t an unmasking of the normal ability of ACTH to regulate aldosterone, secondary to the loss of AII responsiveness, rather than an enhancemen t of ACTH effect.