Time Relations in the Alteration of Thyroid Gland Function in Fowls

PREVIOUS studies have shown that seasonal variations of environmental temperature affect the functional activity of the thyroid gland of fowls. Turner (1948) observed a 15% reduction in thyroxine secretion rate (TSR) of hens from March to May as the mean temperature increased. In two separate lines of New Hampshire fowls maintained in this laboratory, Stahl and Turner (1961) observed significantly higher TSR’s during the winter months than during the summer months. Stahl et al. (1961a) determined the increase in TSR of New Hampshire fowls maintained in a constant temperature chamber held at 40°F. They found that the TSR of these birds increased significantly for varying periods of time and after 190 days of subjection to 40°F., in some birds the TSR continued to increase. However, during the first 8 hours at 40°F., no change in the slope of the curve of thyroidal-I131 release was observed, indicating that the fowl’s pituitary…