PLASMA ALDOSTERONE RESPONSE TO ACTH IN SUBTYPES OF PRIMARY ALDOSTERONISM

SUMMARY 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 2h of upright posture, however, levels were similar among the three groups. 3. During ACTH infusion, aldosterone levels in AII‐U and AII‐R APA were similar, and higher than those in BAH. Because of the higher basal level, the 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 cortisol levels observed in the AII‐R APA group may reflect secretion by AII‐R APA of a cortisol‐like substance that is capable of suppressing ACTH and thus adrenal cortisol production. 5. The tendency of aldosterone to follow the diurnal rhythm of ACTH in AII‐U APA may thus represent an unmasking of the normal ability of ACTH to regulate aldosterone, secondary to the loss of AII responsiveness, rather than an enhancement of ACTH effect.