Direct Evaluation of Pituitary Thyrotropin Reserve Utilizing Synthetic Thyrotropin Releasing Hormone¹

Abstract

Serum TSH levels were measured by radioimmunoassay before and after giving synthetic thyrotropin releasing hormone (TRH) to normal subjects and to patients with thyroid or pituitary disease. Normal individuals responded to TRH with reproducible dose-related increments in serum TSH. Females tended to show a greater response to a given dose of TRH than did males, but sex dependent differences were usually not significant. Daily testing with TRH blunted the TSH response; alternate day testing showed less blunting in preliminary studies. Hyperthyroid patients had undetectable baseline TSH levels; seven of nine failed to respond to TRH. Patients with primary hypothyroidism had an exaggerated response to TRH. Treatment with dexamethasone suppressed their elevated baseline TSH levels but not the response to TRH. Euthyroid patients with pituitary lesions were tested with TRH and were found to have intact TSH reserve in most cases. In general, pituitary surgery or radiation obliterated the response to TRH. Dose-response curves and data illustrating the above responses are presented.