HIND-LEG HEAT-LOSSES IN COLD-EXPOSED RATS

Wistar rats, reared at 22 degrees C, were exposed to 4 degrees C for up to 2 h. During this period, the temperatures of aortic blood (core), thigh muscle and skin were recorded; the blood flow into the skin and muscle of the hind leg was determined with radioactive microspheres; and the arterio-venous balances of oxygen and carbon dioxide, as well as those of lactate, were measured. The data were used to estimate the oxidative and anaerobic energy liberated in the hind leg at the given times, as well as the heat transferred by the blood to the leg tissues. These data were used to calculate the heat balance, and hind leg heat loss during cold-exposure. Despite a doubling in heat production in muscle, this accounted for less than a quarter of all the heat lost by the leg; the difference was made up by a marked increased in the heat carried by the blood, thanks to increased blood how. It can be concluded that in spite of increased local heat production, hind leg muscle thermogenesis falls short of providing the heat needed to maintain hind leg tissue temperatures under cold-exposure.