SEASONAL-VARIATIONS OF THYROID-ACTIVITY IN THE ADULT MALE BADGER, (MELES-MELES L)

Seasonal variations of thyroid activity (radioactive iodide uptake, plasma thyroxine, and biological half-life of the radioactive-labeled thyroxine) were studied in the male badger. These variations were characterized by a maximum occurring at the end of summer and in autumn, and a winter and late spring minimum. A significant spring activity was observed. Thyroid uptake 24 hr after injection of radioactive iodide exhibited a maximum from September to December. A second peak is also observed in April. In winter and summer this parameter was strongly depressed. The annual cycle of plasma thyroxine concentrations presented a biphasic seasonal change with a maximum in summer and autumn, a minimum in winter and a second maximum in spring. The metabolism of exogenous thyroxine was reduced in winter and moderate rates of inactivation were observed in summer and autumn. However, during this latter period there is a short, important increase of the biological half-life of thyroxine. Thyroxine metabolism is accelerated at the end of winter. Relationships to seasonal changes in body weight, general activity cycle and climatic conditions are considered. © 1979.