Response to Thermal Stress in the Rat following Acute Administration of Ethanol

Abstract

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 (T_a) of 17, 25, and 32 °C. The magnitude of the ethanol-induced, hypothermic response was inversely related to T_a, with the decrease in colonic temperature (T_co) at 120 min postinjection ranging from 0.1 °C at T_a32 °C to 3.2 °C at T_a 17 °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 T_a 25 °C and immediate exposure to either T_a 32 or 17 °C. The increase in T_co of ethanol-treated rats was delayed compared to controls following exposure to 32 °C. In addition, tail skin temperature and rate of oxygen consumption of treated rats were significantly lower. The delayed rise in T_co is most likely the result of a reduction in rate of oxygen consumption. When administered ethanol at T_a 25 °C and then exposed to T_a 17 °C, the rats exhibited a significant recovery from the metabolic depression that characterized the administration of ethanol during exposure to T_a 17 ° 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 T_a.

β-Adrenergic Responsiveness in the Rat following Acute Administration of Ethanol

“…The mode o f restraint and attachment o f thermocouple wires for measuring tail skin and co lonic temperatures were identical to that described by Spiers cl al. [28). Oxygen consumption (V ,, ) was mea sured by an open-circuit system.…”

“…(15% solution o f ethanol to saline, w/v at 37 ± I °C) and control animals were administered the same volume o f saline (37 ± I °C), intrapcritoneally. It was determined previously that 3 g ethanol/kg was sufficient to alter thermoregulatory ability o f the rat exposed to T a 26 °C for a minimum of 120 min [28], All animals were subcutaneously injected with 50 pg/kg isoproterenol (Isuprel, Winthrop Laboratories) at 10 min after injection o f cither ethanol or saline. Measurements o f T co, T ik.…”

“…22, 28] and potentiated by a decrease in ambient temperature (Ta). The mechanisms responsible for ethanol-induced hypothermia are not completely understood, but include effects on heat production [7,13,28], heal loss [9], and a possible change in thermal set point o f the body [18. 19].…”