Plasma Dexamethasone Concentrations and Cortisol Suppression Response in Patients with Endogenous Depression*

Abstract

An early escape of plasma cortisol concentrations during a 24-h overnight oral dexamethasone suppression test (DST) has been noted in patients with endogenous depression (ED). Among psychiatric patients this finding is highly specific for ED. Plasma dexamethasone and plasma cortisol concentrations were measured in patients with ED and, for comparison, in patients with nonendogenous depression who maintained normal suppression of plasma cortisol during the DST. There was little variation in plasma dexamethasone concentrations between tests within individual patients. In patients with ED tested both before and after treatment the half-life of dexamethasone in plasma between 9-24 h after its administration was the same as that reported by other investigators in normal subjects between 2-8 h after dexamethasone. Abnormally high plasma cortisol concentrations during the DST were observed in patients with ED in association with normal plasma concentrations of dexamethasone. After treatment, these patients maintained normal suppression of plasma cortisol for 24 h after dexamethasone administration, without any change in their plasma dexamethasone concentrations. Patients with nonendogenous depression and those who had recovered from an episode of endogenous depression maintained normal suppression of plasma cortisol through 1600 and 2300 h after dexamethasone despite having low plasma dexamethasone concentrations at these times. We conclude that the abnormal escape of plasma cortisol concentrations from suppression during the 24-h DST in patients with ED cannot be explained by unusually rapid clearance of dexamethasone from plasma. The results indicate that a central neuroendocrine disturbance is present in patients with ED.