title: The relative potencies of L-T4 and L-T3 on the pituitary-thyroid axis in the Japanese quail.
abstract: We have studied indirectly the relative contribution of the two thyroid hormones T4 and T3 to the feedback regulation of thyrotropin (TSH) secretion in quails, by means of the TRH-test. Adult euthyroid quails received a single injection of thyrotropin-releasing hormone (TRH) (1 or 10 micrograms/100 g body wt) and were killed different times after. Peak level of T4 occurred at 40 min and further served as the TRH-test response. The administration of two different doses of T4 or T3 (0.5 or 2 micrograms/100 g body wt) increased plasma T4 or T3 levels by 3- to 12-fold, respectively, according to the dose. The dose of 0.5 micrograms T4 slightly impaired the TRH-test response, while 2 micrograms rapidly blunted this response. Changes in plasma T3 levels had no deep repercussion on the TRH-test response. It is concluded that the pituitary of the quail is more sensitive to changes in plasma T4 levels than to changes in plasma T3.
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D003370:Coturnix / Q000502:physiology*; D007700:Kinetics; D010902:Pituitary Gland / Q000502:physiology*; D011784:Quail / Q000502:physiology*; D013961:Thyroid Gland / Q000502:physiology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013974:Thyroxine / Q000097:blood* / Q000494:pharmacology*; D014284:Triiodothyronine / Q000097:blood* / Q000494:pharmacology
chemical_list: D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013974:Thyroxine