Ethanol potentiation of carbon tetrachloride hepatotoxicity: possible role for the in vivo inhibition of aldehyde dehydrogenase.

A potentiation of CCl4-induced hepatotoxicity was observed in rats pretreated with ethanol 18 hr prior to CCl4 exposure. Hepatic microsomal aldehyde dehydrogenase (ALDH) was significantly inhibited in animals sacrificed 1 hr following the sequential exposure, however, no more so than in those animals receiving CCl4 alone. The animals receiving ethanol alone had ALDH activity similar to vehicle treated controls. Twenty-four hours following a potentiating dose of ethanol and CCl4 an 81 and 57% decline in NAD+-dependent microsomal and mitochondrial ALDH activity was observed, respectively. Similar results were observed for microsomal and mitochondrial NADP+-dependent ALDH activity. The decline in membrane-bound ALDH was greater in potentiated animals than in those receiving CCl4 alone. A relatively smaller decline in cytosolic ALDH activity was observed in CCl4 treated rats with or without ethanol pre-exposure. The data suggest that inhibition of membrane bound ALDH may be one of the major mechanisms of in vivo potentiation of CCl4-induced hepatotoxicity by ethanol.