A COMPARISON OF SEASONAL CHANGES AND THE EFFECT OF COLD ON THE THYROID GLAND OF THE MALE RAT AND GROUND SQUIRREL (CITELLUS TRIDECIMLINEATUS)

Abstract

Seasonal changes have been reported in the morphology, activity and iodine content of the thyroid gland of many species of wild and domestic animals (Seidell & Fenger, 1912; Hunt, 1923; Coninx-Giradet, 1927; Zalesky, 1935; Tala, 1940; Kayser, 1940; Adams, 1946). In the rat, however, except for a single report on changes in iodine content of the thyroid gland (Seidell & Fenger, 1913), it has apparently been taken for granted that seasonal fluctuations do not occur. Contradictory reports concerning cell height, sensitivity to cold or thyrotrophin (TSH) which, in the past, have been assumed to be due to strain differences, diet etc. might be explainable on the basis of seasonal changes. Although, a detailed description of the seasonal changes in the thyroid gland of the ground squirrel and other hibernators is available (Coninx-Giradet, 1927; Zalesky, 1935; Kayser, 1940; Kayser & Aron, 1938) no objective measurements of these changes have been made.