Thyrotropin Response to Synthetic Thyrotropin-Releasing Hormone in Normal Subjects and in Patients with Nontoxic Goiter

400 μg TRH given intravenously to normal subjects produced a peak serum TSH within 20 or 30 min. TSH levels were significantly increased as early as 10 min. after the injection. An oral dose of 10 mg of TRH gave a slower and more sustained response in normal subjects. The magnitude of the TSH response was directly related to the basal serum TSH level and inversely proportional to the basal concentration of blood thyroxine. No alteration in the normal pattern of TSH response was observed in patients with euthyroid nontoxic goiters. The data obtained from the normal subjects indicate that the magnitude of the pituitary response to TRH is closely related to the level of the circulating thyroid hormones. Thus, in patients with thyroid pathology the significance of the TSH response curve to TRH must be interpreted after taking into account the level of circulating thyroid hormones. This is particulary important before drawing conclusions concerning any primary defect of the hypothalamo-pituitary system in thyroid pathology.