Endocrine responses to thyrotropin-releasing hormone in major depressive disorders

The endocrine response to thyrotropin-releasing hormone (TRH) was studied in severely endogenously depressed patients during illness (n=21) and after recovery (n=18). The thyroid-stimulating hormone (TSH) response to TRH was blunted (ΔTSH < 5 μIU/ml) in over one third of depressives during illness and remained blunted in most even after recovery. There was no correlation between multiple measures of cortisol secretion (the mean 24-hour plasma cortisol, dexamethasone suppression test, and plasma cortisol during the TRH procedure) and the TSH response during illness and after recovery. The TSH and prolactin (PRL) responses to TRH, as well as the baseline PRL, were significantly lower during illness. The role of possible abnormalities in dopamine and/or serotonin in depression contributing to these endocrine disturbances is discussed.