Influence of different concentrations of ethanol on energy expenditure, substrate utilisation, and activity in the...

The acute (one hour) effects of intraperitoneal injections of four concentrations (10%, 30%, 45% and 60%) of a single dose (0.5 g/kg) of ethanol were investigated in unanesthetised rats in an open-circuit calorimeter. Ethanol increased energy expenditure, with the greatest effect being produced by the two lowest concentrations. In contrast, ethanol decreased respiratory quotient, with the greatest effect being produced by the two highest concentrations. The decreased respiratory quotients indicate that ethanol promotes an exclusive reliance on lipids as a source of energy, and further causes lipids to be catabolised for the synthesis of glucose. The peak metabolic effects were produced at a dose that did not significantly affect motor activity, which indicates that the metabolic effects are not secondary to changes in activity. These data support the view that ethanol's effects on energy expenditure and substrate utilisation are mediated by distinct mechanisms. Moreover, since the different metabolic effects were produced by the same ethanol dose, they cannot be due to ethanol's energy content. Thus, ethanol concentration is a major modulator of its effects on energy expenditure and substrate utilisation quite apart from effects due to dose, motor activity or its energy content. This suggests the need to consider the effects of ethanol concentration when analysing ethanol's other pharmacological effects.