To determine if corticotroph nonsuppression, as reflected by β-endorphin nonsuppression, occurs before cortisol nonsuppression (defined as a cortisol level of >140 nmol/L) when examining multiple time points in a day.
The General Medical Clinical Research Center and Inpatient Depression Research Unit, Ann Arbor, Mich.
Multiple blood samples were obtained through an intravenous catheter around the time points of 8 AM, noon, and 4 PM and assayed for β-endorphin and cortisol.
Patients meeting Research Diagnostic Criteria for the diagnosis of major depressive disorder, primary and simple. A total of 73 subjects, both inpatients and outpatients, were studied.
Samples were obtained both at baseline and 1 day after administration of 1 mg of dexamethasone at 11:30 PM.
Measurements and Results:
Overall 39 patients (53%) demonstrated β-endorphin nonsuppression after administration of dexamethasone at any of the three time points, while only eight patients (11%) demonstrated cortisol nonsuppression at any of these time points. Cortisol nonsuppression, but not β-endorphin nonsuppression, was associated with lower concentrations of dexamethasone in plasma. Baseline cortisol and menopausal status were significantly associated with β-endorphin nonsuppression in women.