Role of the Thyroid in Metabolic Response to Low Temperature

¹ From the Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington

Cold-adapted rats, kept at 5°C, and warm-adapted rats, kept at 28°C, were curarized and oxygen consumption; heart rate; muscular activity; rectal, foot and room temperatures recorded during a period at 30°C and during exposure to cold. The experiments were performed before and at varying intervals after thyroidectomy. Oxygen consumption measured at 30°C reached a minimum 8 days after thyroidectomy in the rats kept at 5°C and 12 days after thyroidectomy in the rats kept at 28°C. The half-time for the decline was twice as long for the rats kept at 28°C, indicating that thyroxin stores were being utilized twice as fast by the rats kept at 5°C. Upon exposure to cold the rats responded by an increase in oxygen consumption. Since the response persisted after thyroxin stores had been depleted it is concluded that the metabolic response to cold is not directly dependent upon the amount of circulating thyroxin. Rats kept at 5°C reduced their food intake and lost weight following thyroidectomy, but maintained a high metabolic rate. The significance of these findings are discussed.