Transient fall and subsequent return of high aldosterone secretion by adrenal adenoma during continued dexamethasone administration.

Plasma aldosterone concentration was consistently decreased by 50% or more in 6 patients with aldosterone-producing adenoma on the first day of dexamethasone administration, only to rise subsequently with continued use of dexamethasone while plasma cortisol concentration remained suppressed. The secondary rise in plasma aldosterone was not related to measured changes in known stimuli of aldosterone secretion. It is probable that the observations result from intrinsic alteration of aldosterone synthesis in the adenoma during prolonged ACTH suppression.