Properties of alcohol dehydrogenase and ethanol oxidation in vivo and in hepatocytes.

Studies in this laboratory have been concerned with testing the properties of alcohol dehydrogenase (ADH) in vitro as predictors of ethanol oxidation in the rat in vivo. With the kinetic constants for the extracted enzyme determined under physiological conditions (pH 7.3, ionic strength = 0.25, 38 degrees C), it was possible to predict rates of ethanol elimination in the rat in vivo within +/- 15%. The results indicate that the level of ADH is the major rate determining factor and that physiological levels of free cytosolic NADH have a minor influence (less than or equal to 20%) on the rate of ethanol oxidation in vivo. Those conclusions are supported by results with isolated hepatocytes which, when incubated without other substrates, oxidize ethanol at 1/3 the rate in vivo. Under that condition, titrations with 4-pentylpyrazole show that ADH is not rate determining, and acceleration of NADH reoxidation stimulates ethanol removal. When hepatocyte incubations are supplemented with substrates, ethanol oxidation proceeds at rates similar to those in vivo, and the rates are, as in vivo, determined largely by the cellular content of ADH.