Changes in plasma thyroxine levels during and after spontaneous metamorphosis in a natural population of the green frog, Rana clamitans

Abstract

Plasma thyroxine (T 4) levels were measured by radioimmunoassay in a spontaneously metamorphosing population of green frog, Rana clamitans, tadpoles. In accordance with species previously studied, a sharp rise in plasma T 4 was seen at metamorphic climax, followed by a decline at final transformation. Unlike other species studied thus far, T 4 levels were also moderately high in growing tadpoles (stages X–XIII). These early elevated levels may be due to daily rhythmicity in thyroid secretion coupled with the restricted hours of blood collection used in this study.