EFFECT OF THYROTROPHIN RELEASING HORMONE AND THYROID-STIMULATING HORMONE ON SERUM PROTEIN-BOUND 131I

Abstract

ABSTRACT Seventeen subjects without any clinical or laboratory evidence of thyroidal or pituitary disease were given 1.0 mg thyrotrophin-releasing hormone (TRH) as a rapid iv injection 48 hours after an oral dose of 50 μCi 131I-. In all subjects there was a clear rise in serum PB131I. The elevation in the mean serum PB131I was significant (P<0.01) one hour after TRH, and the mean peak response was noted at 4 hours. It is suggested that this elevation in serum PB131I following TRH administration reflects the effect of the TSH released. In order to find the most suitable method of administration, 1.0 mg TRH was given iv, im, or as a 1 hour infusion. The maximal responses seemed to be independent of the mode of administration. Six subjects were given 3.0 mg TRH iv and 4 others 6.0 mg TRH iv. It was not possible to demonstrate a clear dose-response relationship. In five subjects the serum PB127I and the serum PB131I were measured at the same times following administration of TRH. This showed that the serum PB131I was a more sensitive index of TSH release than the serum PB127I. Twenty-four hours after the TRH injection the same subjects were given 5 IU TSH as a rapid iv or im injection. All subjects responded with a significant rise in serum PB131I. In the subjects who did not respond to TRH the response to TSH allows the differentiation between pituitary and thyroid disease.