While there is no doubt that the thyroid gland is necessary for the survival of experimental animals at low environmental temperatures, there is little agreement on the role that the thyroid hormone plays in metabolism during prolonged exposure to cold. Sensitizing tissues to adrenalin and increasing neuromuscular activity have been suggested as possible actions of thyroxin. However, the primary effect of cold may be to increase utilization of thyroid hormone by the peripheral tissues. Thyroxin requirement normally remains high for prolonged periods of cold exposure when tested by turnover methods and by replacement experiments. Recent investigations have suggested that thyroxin is synergistic with adrenalin in chemical regulation of heat production, a process markedly enhanced with continuous cold exposure.
The requirement for thyroxin in chemical regulation of heat production was investigated by testing the response of curarized rats to cold exposure at varying periods after thyroidectomy.