First-pass gastric mucosal metabolism of ethanol is negligible in the rat.

Ethanol metabolism by gastric alcohol dehydrogenase (ADH) is thought to be an important determinant of peripheral ethanol time-concentration curves (AUCs) in rats and humans. We quantitated this metabolism in rats by measuring the gastric absorption of oral ethanol (0.25 g/kg) and the gastric venous-arterial (V-A) difference of ethanol versus ethanol metabolites (acetate, acetaldehyde, and bicarbonate). Over 1 h, approximately 20% of the ethanol was absorbed from the stomach and 70% was emptied into the duodenum. The gastric V-A difference of ethanol metabolites was less than 4% of that of ethanol. Thus, gastric metabolism accounted for less than 1% (less than 4% of 20% absorbed) of the dose. This negligible metabolism was predictable from the low affinity of gastric ADH for ethanol. In contrast, gastric ADH has a high affinity for octanol, and 66% of this compound was metabolized during gastric absorption. Evidence supporting gastric metabolism of ethanol largely derives from the lower AUCs observed after oral than after intravenous administration; however, we observed increasingly higher AUCs with increasingly rapid portal vein infusions of identical ethanol doses. We conclude that gastric metabolism of ethanol is negligible in the rat, and differences in AUCs ascribed to gastric metabolism may reflect differences in ethanol absorption.