Immunofluorescent detection and localization of thyroxine in blood of adult amphibians.

Indirect immunofluorescent staining was used to detect and localize thyroxine (T4) in blood smears from different species of adult amphibians, namely, Rana pipiens, Rana catesbeiana, Bufo marinus, Xenopus laevis, and Notopthalmus viridescens. Fluorescence, indicative of T4, was observed in both plasma and erythrocytes (RBC) from all individuals of the five species studied. It was weak and diffuse in the plasma and in the cytoplasm of the RBC but was intense in the nuclei (especially the nuclear perimeter) of these cells. The finding of intracellular T4 suggests that thyroid hormone may be of some physiological importance in adult amphibians.