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Research Article Free access | 10.1172/JCI107831

Hyperresponse to Thyrotropin-Releasing Hormone Accompanying Small Decreases in Serum Thyroid Hormone Concentrations

Apostolos G. Vagenakis, Basil Rapoport, Fereidoun Azizi, Gary I. Portnay, Lewis E. Braverman, and Sidney H. Ingbar

Endocrine Division, St. Elizabeth's Hospital, Boston, Massachusetts 02135

Department of Medicine, Tufts Medical School, Boston, Massachusetts 02135

Veterans Administration Hospital, San Francisco, California 94121

Department of Medicine, University of California School of Medicine, San Francisco, California 94121

Find articles by Vagenakis, A. in: PubMed | Google Scholar

Endocrine Division, St. Elizabeth's Hospital, Boston, Massachusetts 02135

Department of Medicine, Tufts Medical School, Boston, Massachusetts 02135

Veterans Administration Hospital, San Francisco, California 94121

Department of Medicine, University of California School of Medicine, San Francisco, California 94121

Find articles by Rapoport, B. in: PubMed | Google Scholar

Endocrine Division, St. Elizabeth's Hospital, Boston, Massachusetts 02135

Department of Medicine, Tufts Medical School, Boston, Massachusetts 02135

Veterans Administration Hospital, San Francisco, California 94121

Department of Medicine, University of California School of Medicine, San Francisco, California 94121

Find articles by Azizi, F. in: PubMed | Google Scholar

Endocrine Division, St. Elizabeth's Hospital, Boston, Massachusetts 02135

Department of Medicine, Tufts Medical School, Boston, Massachusetts 02135

Veterans Administration Hospital, San Francisco, California 94121

Department of Medicine, University of California School of Medicine, San Francisco, California 94121

Find articles by Portnay, G. in: PubMed | Google Scholar

Endocrine Division, St. Elizabeth's Hospital, Boston, Massachusetts 02135

Department of Medicine, Tufts Medical School, Boston, Massachusetts 02135

Veterans Administration Hospital, San Francisco, California 94121

Department of Medicine, University of California School of Medicine, San Francisco, California 94121

Find articles by Braverman, L. in: PubMed | Google Scholar

Endocrine Division, St. Elizabeth's Hospital, Boston, Massachusetts 02135

Department of Medicine, Tufts Medical School, Boston, Massachusetts 02135

Veterans Administration Hospital, San Francisco, California 94121

Department of Medicine, University of California School of Medicine, San Francisco, California 94121

Find articles by Ingbar, S. in: PubMed | Google Scholar

Published October 1, 1974 - More info

Published in Volume 54, Issue 4 on October 1, 1974
J Clin Invest. 1974;54(4):913–918. https://doi.org/10.1172/JCI107831.
© 1974 The American Society for Clinical Investigation
Published October 1, 1974 - Version history
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Abstract

To determine whether pituitary thyrotropin (TSH) responsiveness to thyrotropin-releasing hormone (TRH) is enhanced by small decreases in serum thyroxine (T4) and triiodothyronine (T3), 12 euthyroid volunteers were given 190 mg iodide po daily for 10 days to inhibit T4 and T3 release from the thyroid. Basal serum T4, T3, and TSH concentrations and the serum T4 and TSH responses to 400 μg TRH i.v. were assessed before and at the end of iodide administration. Iodide induced small but highly significant decreases in basal serum T4 (8.0±1.6 vs. 6.6±1.7 μg/100 ml; mean ± SD) and T3 (128±15 vs. 110±22 ng/100 ml) and increases in basal serum TSH (1.3±0.9 vs. 2.1±1.0 μU/ml). During iodide administration, the TSH response to TRH was significantly increased at each of seven time points up to 120 min. The maximum increment in serum TSH after TRH increased from a control mean of 8.8±4.1 to a mean of 13.0±2.8 μU/ml during iodide administration. As evidence of the inhibitory effect of iodide on hormonal release, the increment in serum T3 at 120 min after TRH was significantly lessened during iodide administration (61±42 vs. 33±24 ng/100 ml). These findings demonstrate that small acute decreases in serum T4 and T3 concentrations, resulting in values well within the normal range, are associated both with slight increases in basal TSH concentrations and pronounced increases in the TSH response to TRH. These results demonstrate that a marked sensitivity of TSH secretion and responsiveness to TRH is applicable to decreasing, as well as increasing, concentrations of thyroid hormones.

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