Response to thermal stress in the rat following acute administration of ethanol

Several thermoregulatory responses (i.e., colonic temperature, tail-skin temperature, rate of oxygen consumption) were measured in the rat following acute administration of either saline or 3 g ethanol/kg BW i.p. at ambient temperatures (Ta) of 17, 25, and 32 degrees C. The magnitude of the ethanol-induced, hypothermic response was inversely related to Ta, with the decrease in colonic temperature (Tco) at 120 min postinjection ranging from 0.1 degree C at Ta 32 degrees C to 3.2 degrees C at Ta 17 degrees C. Depression of rate of oxygen consumption (heat production) was a major factor contributing to ethanol-induced hypothermia, with no observed differences in heat loss as assessed by differences in the responses of tail skin temperature. Thermoregulatory responses were also measured following acute administration of ethanol at Ta 25 degrees C and immediate exposure to either Ta 32 or 17 degrees C. The increase in Tco of ethanol-treated rats was delayed compared to controls following exposure to 32 degrees C. In addition, tail skin temperature and rate of oxygen consumption of treated rats were significantly lower. The delayed rise in Tco is most likely the result of a reduction in rate of oxygen consumption. When administered ethanol at Ta 25 degrees C and then exposed to Ta 17 degrees C, the rats exhibited a significant recovery from the metabolic depression that characterized the administration of ethanol during exposure to Ta 17 degrees C. This was most likely related to differences in the clearance of ethanol from blood. The results of this study are consistent with the suggestion that the physiologically significant inhibitory effect of acute administration of 3 g ethanol/kg BW on thermoregulatory responses of rats is manifested at the level of heat production rather than heat loss and that the effect is exacerbated by a reduction in Ta.