| Abstract: | Experiments were designed to determine whether the increased rate of ethanol clearance previously demonstrated in alcoholics, in normal humans and in rats following prolonged alcohol ingestion is due to an increase in activity of enzymes involved in its metabolism. Alcohol was given in various doses to 56 rats, and alcohol dehydrogenase (ADH) and lactic dehydrogenase (LDH) assayed in liver, bile, colon, stomach and small intestine. Results were compared with 13 controls and rats given either actinomycin D or cycloheximide. Results of our experiments clearly show that the activity of ADH and LDH in liver, stomach and small intestine significantly increases with administration of single and repeated doses of alcohol, and the effect persists for a significant time. The effect of alcohol appears to be specific, as increased activity in enzymes not involved in its metabolism was not found. Increased ADH activity could be blocked by actinomycin and cycloheximide which suggests that alcohol induced de novo synthesis of this enzyme protein. The increase in activity of the rate-limiting enzyme, ADH, by its substrate ethanol, provides a plausible explanation for the observed tolerance in both rats and man conditioned by prior administration of alcohol. The increase in LDH, a terminal enzyme involved in ethanol metabolism, provides further indirect evidence that ethanol can be metabolized at a faster rate through the normal pathway. The finding of both ADH and LDH in significant amounts in stomach and small intestine in both normal and alcohol-fed rats suggests that ethanol can be metabolized to a significant extent in extrahepatic sites. This is contrary to the current view that alcohol is metabolized entirely by the liver, and that the multiple metabolic derangements in the alcoholic are the consequence of its obligatory metabolism in that organ. |
