Estimation of thyroxine secretion rate in reindeer, Rangifer tarandus: effects of sex, age and season (original) (raw)

Changes in thyroxine secretion rate (TSR) in response to season, age and sex were studied in reindeer, Rangifer tarandus. 2. The TSR was calculated as the product of (a) disappearance rate (R) of labeled thyroxine/day, (b) the concentration of plasma thyroxine (PT) and (c) the volume of thryoxine distribution space (TDS). 3. All thyroid indices showed no significant change due to the different climatic seasons in the Arctic. 4. The biokinetic parameters of thyroid function (TSR) and (K) decreased markedly with age. Sex has little effect on thyroid activity. 5. In conclusion, the thyroid gland appears to play a relatively minor role in acclimatization of reindeer to the Arctic. YOUSEF M. K. & JOHNSON II. D. (1966a) Calorigenesis of dairy cattle as influenced by thyroxine and environmental temperature. J. Anim. Sci. 25, 150-156. YOUSEI~ M. K. & JOHNSON H. D. (1966b) Calorigenesis of cattle as in8uenced by growth hormone and environmental temperatures. J. Anim. Sci. 25, 1076-1082. YOUSEF M. K. & JOHNSON H. D. (1967a) Calorigenesis of cattle as influenced by hydrocortisone and environmental temperature. J. Anim. Sci. 26, 1087-1093. YOUSEF M. K. & JOHNSON H. D. (1%7b) A rapid method for estimation of thyroxine secretion rate of cattle. J. Anim. Sci. 26, 1108-l 112. YOUSEP M. K. & JOHNSON H. D. (1968) Effects of heat and feed restriction during growth on thyroxine secretion rate of male rats. Endocrinology 82, 353358. YOUSIXF M. K. & JONNSON H. D. (1970) Se76-selenomethio~e turnover rate during growth and aging in rats.