The control of shivering and non-shivering thermogenesis in the rat.

1. The effect of intraperitoneal administration of propranolol (4, 8 and 12 mg/kg) on colonic temperature was studied in twelve rats during exposure to ambient temperatures of 30, 15 and 5 degrees C. 2. At 30 degrees C, propranolol had no effect on colonic temperature; at 15 and 5 degrees C, however, 4 mg propanolol/kg induced a fall in colonic temperature of about 0-8 degrees C, whereas 8 and 12 mg propanolol/kg induced a fall of about 1-5-2-0 degrees C. 3. Assuming that the temperature regulations system of the rat has a proportional controller and that the effect of propranolol was due to the blockade of non-shivering thermogenesis, the results are interpreted as showing that shivering is activated only when heat loss exceeds the capacity for non-shivering thermogenesis.