Original Articles ; Effect of an Acute Ethanol Administration of Rat Liver Alcohol Dehydrogenase

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the main enzymes responsible for ethanol metabolism in the liver. In the present study, effect of an acute administration of ethanol on activities of hepatic ADH and ALDH was investigated in starved rats fed ethanol at a dose of 3 g/㎏ body weight (bw). ADH and ALDH activities were measured at 1, 2, 4, and 6 h after the ethanol treatment. The acute administration of ethanol caused an inhibition of cytosolic ADH enzyme in the liver at 1 h, and this inhibition remained until 6 h after the ethanol intake. In contrast to ADH, mitochondrial ALDH activity was not affected by ethanol at early times. However, it was slightly reduced at 6 h after ethanol intake. Factors that may regulate ADH activity in ethanol-fed rats were examined. ADH activity was measured in the presence of various concentrations of ethanol or acetaldehyde in assay mixture containing hepatic cytosolic fraction prepared from rats fed a chow diet, in order to determine whether the substrate (ethanol) or the product (acetaldehyde) of this enzyme inhibits ADH. Both ethanol and acetaldehyde inhibited ADH enzyme at high concentrations. However, ADH inhibition by acetaldehyde disappeared after dialysis. An ethanol disappearance curve was constructed to determine the elimination rate constant for ethanol, k^(el), and the blood lactate/pyruvate (L/P) ratio was measured to estimate the redox state in the liver during ethanol metabolism. The k^(el), value was calculated to be 0.092/min and the blood L/P ratio increased 16.6% by ethanol treatment. The combined data suggest that the decrease in hepatic ADH activity observed in rats fed ethanol is probably due to an inhibition caused by local, high concentrations of ethanol and acetaldehyde in the cytosol of the liver and that the inhibition of ADH by acetaldehyde is reversible.