Abstract
There was a significant rise in serum TSH levels in normal subjects given TRH either intravenously or subcutaneously. Serum TSH was also increased by oral administration of TRH but the response was considerably lower. The serum TSH increased rapidly to reach the maximum level about 30 min after intravenous administration of 50-800μg of TRH and the response appeared to be related to the quantity of TRH. The maximum response ranged from 10 to 40μU/ml by 500μg of TRH. Day to day variation of the response in a single individual was smaller than variations in different subjects. Serum GH, LH and cortisol levels did not show any significant changes following administration of TRH. Intravenous administration of 500 to 800 pg of TRH failed to alter serum thyroxine levels, but 10mg of TRH given orally caused a slight but consistent rise in the serum thyroxine level.
A clinical test, designated as TRH test, was standardized on this basis and performed in patients. The response to the test varied considerably from patients to patients with hypothalamico-pituitary diseases, i. e. hypopituitarism resulted from postpartum necrosis, meningitis, pituitary dwarfism, chromophobe adenoma, acidophile adenoma, craniopharyngioma and chordoma. In general, no response at all or a low one was noted in patients with secondary hypothyroidism. No response was noted in two female siblings with non goitrous cretinism due to isolated thyrotropin deficiency. In patients with untreated Graves' disease, the base line TSH was undetectable in most cases and did not respond to TRH. The patients rendered euthyroid by antithyroid therapy had also no response at all or a low one to TRH. Serum TSH levels which were very high in patients with primary hypothyroidism were markedly more increased following TRH administration. During treatment with desiccated thyroid, both the base line and the response to TRH were lowered. Dilution curves in radioimmunoassay with sera obtained from a patient before and 30 min after TRH administration were parallel with a standard curve with the standard TSH.
