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

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Abstract
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.

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