Sensitivity of thyrotropin (TSH) secretion to 3,5,3'-triiodothyronine and TSH-releasing hormone in rat during starvation.
The mechanisms by which plasma T3 and TSH decrease after a 3-day starvation period are not completely understood. In this study we tested the hypothesis of a possible modification in the sensitivity of thyrotroph cell to T3 and/or TRH. For that purpose, TRH tests were performed before and after a 3-day starvation in euthyroid, thyroidectomized, and T3-treated (75 or 175 ng/100 g BW) thyroidectomized male Wistar rats. TRH (10 to 500 ng/100 g BW) was injected iv through a chronically-implanted catheter. In another set of experiments, hypophyseal TSH content was also determined. Our results showed that after a 3-day-starvation plasma TSH decreased in all except hypothyroid rats; TSH responsiveness to TRH was unchanged in euthyroid rats but was increased in hypothyroid rats; and the T3-dependent increase in TSH responsiveness to TRH was significantly amplified. Moreover, there was a significant positive correlation between TSH responsiveness to TRH and hypophyseal TSH content. These results suggest that starvation induces an increased sensitivity of thyrotroph cell to T3.
D000818:Animals; D005508:Food Deprivation; D007037:Hypothyroidism / Q000503:physiopathology; D008297:Male; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013217:Starvation / Q000503:physiopathology*; D013961:Thyroid Gland / Q000503:physiopathology; D013972:Thyrotropin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000097:blood / Q000502:physiology*; D014284:Triiodothyronine / Q000097:blood / Q000502:physiology*
D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin