The effect of a single injection of thyrotrophin on serum concentrations of thyroxine, triiodothyronine, and reverse triiodothyronine in the immature chicken (Gallus domesticus).

Immature domestic fowl were given a single injection of 0.1 or 0.25 IU bovine thyrotrophin (TSH)/kg body wt by the intramuscular route and serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), and 3,3',5'-reverse T3 (rT3) were measured during the following 24 hr. The increase in T4 was markedly greater than that of T3. Serum rT3 concentration increased after an injection of 0.25 IU TSH/kg but the maximal concentration (75 pg/ml) was very low.