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Starvation Induces a Partial Failure of Triiodothyronine to Inhibit the ThyrotropinResponse to Thyrotropin-Releasing Hormone^*

ALBERT G. BURGER, MICHAEL WEISSEL and MICHAEL BERGER

Thyroid Research Unit, Endocrine Division, and Institut de Biochimie Clinique, University of Geneva Switzerland

Address requests for reprints to: Dr. A. Burger, Thyroid Research Unit 4-767, Hopital Cantonal CH-1211 Geneva 4, Switzerland.

During starvation the response of TSH to TRH decreases in many subjects. This could be due to an increased sensitivity of TSH secretion to circulating thyroid hormones. To study this hypothesis,13 subjects were starved twice for 2-day periods. After both starvation periods, a standard TRH test (200 µg TRH, iv) was performed; during 1 starvation period 15 µg T₃ were injectediv 24 h before the TRH test. The TRH tests were also performed while on normal nourishment, once without pretreatment and once 24 h after the iv injection of 15 µg T₃.

The spontaneous decrease of the TSH response to TRH was seen in 10 of 13 subjects. In these 10 subjects it decreased from 180 ± 1.9 to 9.7 ± 1.2 µU/ml (mean ± SEM; P < 0.001). The additional inhibition of the TRH test with T₃ was small compared with the one observed under normal conditions. In starvation, T₃ decreased the maximal TSH response from 9.7 ± 1.2 to 8.4 ± 1 µU/ml (P = NS), while during the control period the maximal TSH response fell from 18.0 ± 1.9 to 11.4 ± 1.3 µU/ml (P < 0.001). These data indicate a diminished effectiveness of T.t in inhibiting TSH secretion and are consistent with the hypothesis of a more generalized resistance of target organs to T₃ during starvation in man.

^* This work was supported by the Swiss National Research Foundation (Grant 3.925–0.78).

f Supported by the Swiss-Austrian Fellowship for Scientific and Technical Collaboration. Present address: Second Medical Department,University of Vienna, A-1090 Vienna, Austria.

Present address: Department of Medicine E, Diisseldorf University,4 Diisseldorf, West Germany.

Received April 9, 1980.

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