(a) The delayed TSH response to TRH in a patient with hypothalamic disease. Peak plasma TSH values are reached at approximately 60 minutes following exogenous TRH, compared to the normal where the peak occurs at 20ΓÇô30 minutes pituitary hypothyroidism, TSH reserve may be severely reduced and there may be only a slight, or no response, to exogenous TRH. (b) The normal rise in circulating plasma T3 following an injection of TRH. The T3 response lags behind the TSH response, reflecting the fact that T3 rises secondary to stimulation of the thyroid gland by the released TSH.
