Nuclear receptors for L-triiodothyronine in quail liver

Binding studies were conducted using in vitro-labeled quail liver nuclei to identify and characterize receptors for L-triiodothyronine (T3). Saturation binding experiments were analyzed by Scatchard analysis and indicated a single class of high-affinity, limited-capacity T3 binding sites. These receptors exhibited binding specificity as demonstrated by competition experiments between labeled T3 and unlabeled thyroid hormones or hormone analogs. Binding specificity was virtually identical in quail and rat liver nuclei. Thus, apparent differences between mammals and birds, in regard to the biological potency of T4 versus T3, are not apparent at the level of the nuclear T3 receptor.