THE TEMPERATURE RESPONSE OF ACCLIMATIZED AND UNACCLIMATIZED RATS TO EXERCISE IN THE COLD

Abstract

Colonic and tail-skin temperatures of cold-acclimatized (4 °C for 4 weeks) and unacclimatized (4 °C for 1 day) rats were measured while they were being exercised on a treadmill (4.6 m/minute) in the cold (4 °C). In unacclimatized animals the colonic temperature increased to the same level as when they were previously exercised at 24 °C, but the changes in tail-skin temperature indicated only a small vasodilatation. In cold-acclimatized animals the colonic temperature increased to a significantly higher level than in unacclimatized animals before peripheral vasodilatation appeared, and this higher colonic temperature was maintained as exercise continued. In addition, the cold-acclimatized animals showed a higher tail-skin temperature during rest and a greater vasodilatation during exercise than the unacclimatized controls. Rats treated for 6 days at room temperature (24 °C) with a mixture of thyroxine (25 μg/100 g body weight per day) and cortisone (1 mg per rat per day) were exercised at 4 °C after being exposed to this temperature for only 1 day. The colonic temperature was controlled at a higher level in these animals than in saline-injected controls but peripheral vasodilatation was not greater.