THE INFLUENCE OF ENVIRONMENTAL TEMPERATURE ON THE METABOLISM OF THE THYROID HORMONE IN THE RAT*

IT HAS been conclusively demonstrated that in many animals, including the rat, an increase in thyroid activity occurs on exposure to cold. (Ring, 1939; Uotila, 1939; Dempsey and Astwood, 1943). Uotila (1939) has shown that the pituitary stalk is a necessary link in the thyroid stimulation but beyond this, the mechanism of the response is obscure. In an attempt to elucidate further the manner in which exposure to cold causes an increase in the activity of the thyroid gland, we have studied the effect of environmental temperature on the serum protein-bound iodine first, in untreated rats, and second, in rats maintained on propylthiouracil and graded doses of thyroid. In the latter experiments, in which the rate of supply of thyroid hormone is known, one can obtain an index of the rate of utilization of thyroid hormone and can determine whether or not the increased utilization in rats exposed to cold is dependent upon an increase in the concentration of hormone in the blood stream.