THYROXINE CONCENTRATIONS IN BLOOD-SERUM AND PERICARDIAL FLUID OF METAMORPHOSING TADPOLES AND OF ADULT FROGS

Thyroxine (T4) was measured by double antibody radioimmunoassay in blood serum and pericardial fluid of individual tadpoles and frogs of Rana catesbeiana. The pattern of change of mean T4 values during tadpole growth and metamorphosis was similar in serum and pericardial fluid. In growing tadpoles, stages V-XVIII, all T4 concentrations were below the limit of detection (<0.20 μg/dl). Mean T4 values first became detectable in early metamorphic stages, XIX, XX; they reached a peak (0.94 μg/dl serum) at stages XXI, XXII, XXIII. Differences in mean values between these three stages were not significant. At the end of metamorphosis, stages XXIV, XXV, mean T4 concentrations dropped to levels similar to those of stages XIX, XX. However, in adult summer frogs mean T4 values for serum and pericardial fluid were somewhat higher than mean values at the end of metamorphosis. Despite this general developmental pattern, T4 concentrations in some individual animals at each stage, including metamorphic stages, were below the limit of detection (<0.20 μg/dl). © 1979.