Pituitary sensitivity to thyroid hormones in depressed patients.

To evaluate the feedback control of thyroid hormones on TSH release, 18 normal subjects and 16 depressed patients received two TRH injections: on days one and nine. Forty eight hours before the second TRH injection subjects and patients received either T3, 100 micrograms orally, or matched placebo. T3 administration resulted in a highly significant and similar reduction of delta max TSH and FT4-index levels in both subjects and patients whereas serum T3 levels were unchanged. These data suggest that the pituitary response to the negative feedback signal of T3 is intact in depressed patients.