Magnitude, Origin, and Implications of the Discrepancy between Blood Ethanol Concentrations of Tail Vein and Arterial Blood of the Rat

The rat is widely used as an animal model for experiments involving ethanol, and alcohol concentrations in blood obtained from the tail routinely are used to monitor ethanol exposure and metabolism. The present study demonstrates that during periods of rising and declining ethanol levels, the alcohol concentrations in tail vein blood lags far behind that of arterial, jugular, or femoral vein blood. As a result, tail vein ethanol concentrations markedly underestimate the concentration in arterial blood and rapidly perfused tissue during periods of increasing body ethanol, whereas the reverse is true as body ethanol declines. This discrepancy, which appeared to result from the low blood perfusion:tissue water ratio in the tail, disappeared when the tail was heated to 37°C. Compared with arterial blood, alcohol measurements performed on tail vein blood yielded a much higher apparent K_m for ethanol clearance and a somewhat lower estimate of ethanol reaching the peripheral circulation. We conclude that, for a variety of studies, analyses of arterialized blood from the heated tail should yield a more accurate and reproducible measure of ethanol exposure and/or metabolism than does the conventional collection from the unheated tail.