Alteration of Thyroid Hormone Secretion Rate in Fowls Changed from a Cold to a Warm Environment

THE seasonal variation in thyroxine secretion rate (TSR) of two strains of New Hampshire fowls differing in mean TSR has been reported (Stahl and Turner, 1961). The group of fowls with a high mean TSR secreted the equivalent of 2.97 μg. l-thyroxine (l-T4)/100g. body weight (b.w.) during the winter months and declined to 1.24 μg. l-T4/100g. b.w. during the summer months, a decline of 58.3%. The low TSR strain showed a mean TSR of 1.01 μg. l-T4/100g. b.w. in the winter and 0.59 μg. l-T4 in the summer, a decrease of 41.6%. These changes are gradual with increasing and decreasing environmental temperature. The mechanism by which the animal body adjusts to temperature variation involves the increased secretion of the thyrotropic hormone (TSH) and of l-T4 during periods of a cold environment and decreases during periods in a hot environment. When these fowls were shifted suddenly from a warm environment to …