EFFECT OF COLD-EXPOSURE ON ORGAN TEMPERATURES IN WISTAR AND ZUCKER FA/FA RAT

1. Small thermocouple sensors were surgically implanted in several organs of Wistar and Zucker fatty (fa/fa) rats. The sensors allowed continuous long-term monitoring of the temperatures of the organs cited in otherwise undisturbed rats. 2. In Wistar rats, brown adipose tissue, liver and kidney temperatures were consistently higher than core (aortic) temperature: in Zucker fa/fa rats, only liver, kidney and small intestine showed higher temperatures than that of the blood. 3. During cold (4-degrees-C) exposure, Wistar rats maintained their core blood temperature, whilst Zucker fa/fa rats showed a deep hypothermia that was potentially lethal; under cold exposure all organs studied showed changes which were parallel to changes in aortic blood temperature. Zucker fa/fa rats were unable to maintain their temperature under cold conditions. 4. The results obtained suggest that in Wistar rats there must be net export of heat from liver, kidney and brown adipose tissue. No persistent effect of muscle shivering thermogenesis was observed.