Effects of alcohol consumption on mitochondrial aldehyde dehydrogenase isoenzymes in rat liver

The effects of long-term and short-term exposure of rats to ethanol on aldehyde dehydrogenase (ALDH) activity in the liver mitochondria were investigated. The specific activities of mitochondrial high Km ALDH and low Km ALDH after the prolonged administration of ethanol were both increased to levels about 2.5 times that of the control group. In contrast, high Km and low Km ALDH showed maximum activity 12 h after administration of a single large dose of ethanol, increasing 21 and 4.4 times, respectively, over the level in the control group. When ethanol was administered for a long time, the two ALDH isoenzyme levels showed approximately the same increase, while the high Km ALDH level was more significantly increased than the low Km ALDH level after a single large dose. These results suggest that the high Km ALDH level of the outer membrane was increased as a result of a transient increase in the level of acetaldehyde around the liver mitochondria after a single large dose of ethanol, and that high Km ALDH plays an important role in acetaldehyde metabolism. However, when ethanol was administered for a long time, the mitochondria were exposed to low concentrations of acetaldehyde over a long time, leading to an increase in levels of low and high Km ALDH in the matrix.