THYROXINE SECRETION IN RATS EXPOSED TO COLD1

Abstract

THE importance of the thyroid hormone in the increased heat production necessary for survival in a cold environment has been established in the rat (1). Several indices, including histological changes (2, 3, 4), the effects of anti-thyroid substances (5, 6) and iodine metabolism (7, 8) indicate that thyroid activity increases shortly after exposure to cold and remains high for some time. However, whether a high level of thyroid activity continues throughout prolonged cold exposure has been questioned. In various studies, values obtained by several indirect indices of thyroid activity have returned to, or toward normal after about 30 or more days' cold exposure.