Noradrenergic response to acute ethanol administration in heathly subjects: comparison with intravenous yohimbine

The effects of oral administration of ethanol [1.1 ml/kg 95% ethanol administered as a 20% (by volume) solution] and intravenous administration of the alpha₂ adrenergic receptor antagonist yohimbine hydrochloride (0.4 mg/kg), alone and in combination, were compared using a double-blind, placebo-controlled design. Twelve healthy subjects completed 4 test days during which drug effects on subjective measures of intoxication and anxiety, plasma levels of the norepinephrine (NE) metabolite 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) and cortisol, and cardiovascular indices were assessed. Acutely administered oral ethanol significantly increased the subjective measures of intoxication and anxiety, plasma MHPG, and sitting systolic blood pressure compared with placebo. Intravenous yohimbine significantly increased subjective measures of intoxication and anxiety, plasma MHPG and cortisol, and blood pressure relative to placebo. The ethanol-induced increase in plasma MHPG was significantly greater than that following yohimbine, whereas yohimbine resulted in significantly greater increases in anxiety, plasma cortisol, and blood pressure measurements than ethanol. The combined administration of ethanol and yohimbine had a clear additive effect of increasing the severity of acute intoxication compared with ethanol or yohimbine alone, and resulted in a significantly greater plasma MHPG response compared with either drug given alone. Although the pharmacokinetic effects of ethanol administration on NE metabolism must be considered, these findings suggest that the intoxicating and anxiogenic effects of acute ethanol administration may be associated with increased NE turnover, as measured by plasma MHPG, in healthy human subjects. In addition, these results indicate that ethanol and yohimbine may act additively to increase ethanol intoxication and that they may increase NE turnover through different physiological mechanisms.