Beta-adrenergic responsiveness in the rat following acute administration of ethanol

Ethanol has been shown to induce a hypothermia in rats maintained in air at 26 degrees C. The objective of the present study was to assess the metabolic responsiveness of ethanol-treated rats to administration of isoproterenol, a beta-adrenoceptor agonist, and to assess whether ethanol per se, or the hypothermia accompanying its administration, contribute to changes in beta-adrenergic responsiveness. In the present study, administration of ethanol (3 g/kg, i.p.) reduced both colonic temperature (Tco) and rate of oxygen consumption (metabolic rate) of rats maintained at 26 degrees C to levels below those of saline-treated controls within 20 min after treatment. Maximal decreases in both parameters occurred within approximately 40 min. Administration of isoproterenol (50 micrograms/kg, s.c.) 10 min after treatment with either ethanol or saline was accompanied by an increase in the metabolic rates of both groups, although the magnitude of the increase in the ethanol-treated group was less than that of controls. Maximal increases in tail skin temperatures (Tsk) following treatment with isoproterenol were similar in both groups but an increase in Tsk occurred earlier in the ethanol-treated group. Tco increased after treatment with isoproterenol in the saline-treated group but decreased in the ethanol-treated group. When isoproterenol was administered 90 min after treatment with ethanol, increases in metabolic rate, Tsk, and Tco were similar in both groups, although the increase in Tsk of ethanol-treated animals was delayed until Tco reached pretreatment level. Exposure to 30 degrees C minimized ethanol-induced hypothermia. At this temperature the metabolic responses to administration of isoproterenol at 90 min after treatment with ethanol did not differ significantly between the two groups. These results suggest that the metabolic responsiveness to administration of a beta-adrenoceptor agonist is not altered by prior treatment with ethanol but is affected by the hypothermia accompanying its administration.