Pituitary and Peripheral Hormone Responses to T3 Administration During Antarctic Residence
NAVAL MEDICAL RESEARCH INST BETHESDA MD
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Very little is known regarding hormonal adaptation in human subjects who are exposed to the extremes of temperature and light that are found in polar latitudes. We have previously reported a 50 elevation in the serum thyrotropin TSH response to thyrotropin-releasing hormone TRH, a fall in serum total triiodothyronine T3 and free T3 fT3, and no change in serum total thyroxine T4 or free T4 fT4 after 42 wk of Antarctic cold exposure. To differentiate between central and peripheral mechanisms that may lead to these changes, we report the effect of sequentially increasing oral doses of T3 Cytomel on serum T3 and fT3 levels and on the resultant attenuation of the TSH response to TRH in nine men before, during, and after 42 wk residence in Antarctica. The pituitary response to TRH was attenuated by each T3 regimen and this suppression was not different after 20 and 42 wk of Antarctic residence. Serum T4 and fT4 values were similar throughout the study. We conclude that the pituitary sensitivity to T3 was unchanged during the study and that changes in TSH responsiveness and serum T3 levels were likely due to changes in peripheral T3 metabolism. Keywords Thyrotropin Thyrotropin-releasing hormone Cold adaptation Reprints.
- Anatomy and Physiology