Circadian secretion of ACTH, cortisol, and mineralocorticoids in Cushing's syndrome.

The behaviour of plasma levels of ACTH was studied in five untreated patients with pituitary-dependent Cushing's syndrome, with blood samples taken every half an hour for a total period of 24 hours; plasma cortisol, corticosterone, deoxycorticosterone (DOC) and aldosterone were also measured simultaneously. In all cases, above normal secretory impulses of ACTH and cortisol, at approximately the same height, were present throughout the day, while between these peaks the levels were in the normal range. Few peaks of ACTH and cortisol were simultaneous and rare secretory impulses of corticosterone, and deoxycorticosterone were in synchrony with those of ACTH or cortisol. DOC levels were found to have some peaks above normal levels while corticosterone levels presented rare elevated peaks during the day. Plasma aldosterone values on the other hand, were extremely low in all except in one case, where the variations may be interpreted as pure fluctuations. These findings confirm that: 1) In a number of cases, multiple samples of ACTH and cortisol (during the 24 hrs.) appear to be essential in order to distinguish pituitary-dependent Cushing's syndrome from normal; 2) In conditions of ACTH excess, DOC and corticosterone secretion seems to become progressively less ACTH-dependent as we proceed down the biosynthetic chain towards aldosterone, which is suppressed in most cases.