Effects of ethanol and tertiary-butanol on energy expenditure and substrate utilization in the rat

Does an Energy Drink Modify the Effects of Alcohol in a Maximal Effort Test?

BACKGROUND

There are popular reports on the combined use of alcohol and energy drinks (such as Red Bull and similar beverages, which contain caffeine, taurine, carbohydrates, etc.) to reduce the depressant effects of alcohol on central nervous system, but no controlled studies have been performed. The main purpose of this study was to verify the effects of alcohol, and alcohol combined with energy drink, on the performance of volunteers in a maximal effort test (cycle ergometer) and also on physiological indicators (oxygen uptake, ventilatory threshold, respiratory exchange rate, heart rate, and blood pressure), biochemical variables (glucose, lactate, insulin, cortisol, ACTH, dopamine, noradrenaline, and adrenaline), and blood alcohol levels.

METHODS

Fourteen healthy subjects completed a double-blind protocol made up of four sessions: control (water), alcohol (1.0 g/kg), energy drink (3.57 ml/kg Red Bull), and alcohol + energy drink, each 1 week apart. The effort test began 60 min after drug or control ingestion, and the dependent variables were measured until 60 min after the test.

RESULTS

Heart rate at the ventilatory threshold was higher in the alcohol and alcohol + energy drink sessions in comparison with control and energy drink sessions. Although in comparison to the control session, the peak oxygen uptake was 5.0% smaller after alcohol ingestion, 1.4% smaller after energy drink, and 2.7% smaller after the combined ingestion, no significant differences were detected. Lactate levels (30 min after drug ingestion, 30 and 60 min after the effort test) and noradrenaline levels (30 min after the effort test) were higher in the alcohol and alcohol + energy drink sessions compared with the control session.

CONCLUSIONS

The performance in the maximal effort test observed after alcohol + energy drink ingestion was similar to that observed after alcohol only. No significant differences between alcohol and alcohol + energy drink were detected in the physiological and biochemical parameters analyzed. Our findings suggest that energy drinks, at least in the tested doses, did not improve performance or reduce alterations induced by acute alcohol ingestion.

Insulin increases energy expenditure and respiratory quotient in the rat

The effects of insulin on energy expenditure are a matter of dispute. Various authors have reported increases or decreases. Irrespective of their nature, it is not clear whether the effects of insulin on energy expenditure are secondary to insulin-induced hypoglycemia or changes in motor activity. The present study investigated the acute effects of insulin on energy expenditure, energy substrate utilisation, motor activity and blood glucose levels. Four U/kg of fast acting insulin had no effect on any of the metabolic or motor activity measures in spite of producing a 30% reduction in blood glucose levels. In contrast, 8 U/kg of insulin increased energy expenditure and respiratory quotient, with the latter effect indicating increased reliance on carbohydrates as a source of energy. This dose reduced blood glucose levels by 68%, yet had no significant effect on motor activity. Insulin, therefore, enhances thermogenesis and carbohydrate utilisation in a manner that can be dissociated from any effect on motor activity. These effects occur at a high dose and they are not counteracted by even massive hypoglycemia. It, therefore, appears that in terms of energy expenditure insulin may be characterised as catabolic, whereas in terms of substrate utilisation it may be characterised as anabolic.

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

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.

Effects of ethanol and tertiary butanol on blood glucose levels and body temperature of rats

The mechanisms of ethanol's hyperglycemic and hypothermic effects were investigated by comparing the effects of ethanol with those of tertiary butanol. Tertiary butanol is an intoxicant like ethanol, but unlike ethanol it is only minimally metabolized. Consequently, tertiary butanol does not produce appreciable amounts of active metabolites or energy. Tertiary butanol exerts its neural effects primarily by directly altering the physico-chemical properties of nerve cell membranes. It was found that ethanol and tertiary butanol produce hyperglycemic and hypothermic effects whose magnitude and time course are nearly identical. These data suggest that the hyperglycemic and hypothermic effects of ethanol represent a primary physico-chemical effect on nerve cell membranes and are not secondary to its energy content or metabolites.