Receptor Induction by Thyroid Hormones in Tadpole Erythrocytes in Vivo and in Vitro

Abstract

This paper describes the continuation of studies of the binding of the thyroid hormone (TH) or triiodothyronine (T3) to nuclei of red blood cells (ABCs) of Rana catesbeiana tadpoles (1–4). Nuclei of tadpole liver and tail contain specific binding sites for TH which may affect the dramatic changes in these tissues during metamorphic climax. Moriya et al. (4) have detected saturable, high affinity binding of T3 in tadpole RBC nuclei. They also found that the number of binding sites per nucleus increased four to five times during the approach to metamorphic climax or in response to an injection of T3. Similar results were reported independently by Galton et al. (5,6). Suggestions that the nuclear binding sites in tadpole RBCs are TH receptors have been based primarily on their binding characteristics and the presumption that the receptor increase is of physiological significance. Therefore, we have investigated receptor induction, the proposal that the increase in T3 binding sites is a direct response of the RBCs to T3, and that the binding sites are T3 receptors (1–6).