The TRH stimulation test in subtypes of unipolar depression.

The thyrotropin releasing hormone (TRH) stimulation test was administered to 54 primary unipolar endogenously depressed and 19 non-depressed hospitalized inpatients. Blunted TSH responses to TRH infusion (delta max TSH less than 7 microunits/ml) were revealed in 18 depressed and no non-depressed patients (P less than 0.01). Augmented TSH responses (delta max TSH greater than 23 microunits/ml) were noted in 8 depressed and no non-depressed patients (P = n.s.). The TRH stimulation test did not distinguish between subtypes of unipolar depression using the familial subtyping criteria of Winokur. These findings are discussed in light of previously reported dexamethasone suppression test subtype distinctions.