Plasma ACTH levels in primary depression: relationship to the 24-hour dexamethasone suppression test.

The failure of adequate cortisol suppression after 1 mg dexamethasone in 50% of patients with endogenous depression has been attributed to abnormal hypothalamic-pituitary-adrenal axis regulation, resulting in high levels of adrenocorticotropic hormone (ACTH). Because studies of plasma ACTH have been conflicting, we studied plasma ACTH levels during the 24-hour dexamethasone suppression test in a homogeneous group of 29 hospitalized patients with primary endogenous depression and 19 normal volunteers. No differences were found in ACTH levels among normal volunteers, depressed cortisol suppressors, and depressed cortisol nonsuppressors at either 4 p.m. or 11 p.m.