Compensatory pituitary-thyroid mechanisms in major depressive disorder

The thyrotropin-releasing hormone (TRH) stimulation test was administered to 47 patients meeting DSM-III criteria for major depressive disorder (with melancholia) and to 19 nondepressed patients. The wide variability of pituitary responses to TRH stimulation noted in the depressed patients provides evidence for the dysregulation of compensatory hypothalamic-pituitary-thyroid function in acute depression. Blunted thyroid-stimulating hormone (TSH) responses to TRH injection were found in 16 depressed (34%) and no nondepressed patients (p less than 0.01). Depressed patients who revealed blunted TSH responses also had blunted prolactin responses to TRH relative to other depressed and nondepressed patient groups (p less than 0.01). These patients (with blunted TSH and prolactin responses) may represent a psychobiologically distinct subgroup of endogenously depressed patients. Augmented (high normal) TSH responses to TRH stimulation were found in eight depressed patients (all women), in contrast to no nondepressed patients. These patients may have a subtle thyroidal dysfunction affecting the underlying endogenous depressive diathesis.