Diurnal variation in plasma cortisol and prolactin in patients with Cushing's syndrome.

Abstract

ABSTRACT To evaluate the relationship between plasma prolactin and cortisol in patients with Cushing's syndrome, the 24 h pattern of these hormones was measured in normal subjects and in 5 patients with pituitary dependent Cushing's syndrome and 2 patients with Cushing's syndrome due to an adrenocortical adenoma and ectopic secretion of ACTH. The normal subjects showed an increase in plasma prolactin during late sleep without correlation (P > 0.05) to changes in plasma cortisol. All patients had normal basal levels (between 10 a. m. and 12 p. m.) of plasma prolactin. Four of 5 patients with pituitary dependent Cushing's syndrome had an absent diurnal rhythm of plasma prolactin. One patient classified as pituitary dependent Cushing's syndrome on the basis of adrenal pathology, but pituitary independent on the basis of the dexamethasone suppression test had a normal circadian rhythm of plasma prolactin suggesting that the disease is not pituitary dependent at this stage. Two patients with pituitary independent Cushing's syndrome, one with adrenocortical adenoma and one with an oat cell carcinoma of the lung and the ectopic ACTH syndrome and very elevated plasma cortisol levels showed a normal and an absent diurnal rhythm of prolactin, respectively.