Pathways of Ethanol Metabolism in Perfused Rat Liver

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Abstract
Traditionally, ethanol metabolism is a function attributed solely to the hepatic enzyme alcohol dehydrogenase (ADH) (1). Whereas the importance of the liver as the primary organ of ethanol metabolism remains unchallenged (2), recent years have seen the accumulation of evidence indicating that enzyme systems other than alcohol dehydrogenase participate in the metabolism of ethanol (3, 4,5). However, the identity of the enzyme(s) responsible for ADHindependent ethanol metabolism is a subject of great controversy (6,7,8). Evidence has been presented in favor of the catalase-hydrogen peroxide complex (4,5) and, in turn, for the so-called Microsomal Ethanol Oxidizing System (MEOS) (3,9) as additional hepatic ethanol-oxidizing systems. Extrapolations from inhibition studies performed in vitro to in vivo situations have created a great deal of confusion concerning the quantitative role of ADH as well as of other possible pathways. The present study will both review the problems involved in the evaluation of the pathways of ethanol metabolism and describe a combination of experimental techniques which make it clear that ethanol is metabolized principally by alcohol dehydrogenase at low ethanol concentrations (5). On the other hand, at high ethanol concentrations, catalase participates in ethanol metabolism to a significant degree.