Adaptive changes induced by chronic ethanol ingestion on hepatic mitochondrial and microsomal enzyme activities

Abstract

Ethanol exerts its pharmacological effects by altering the physico-chemical properties of biological membranes. Modifications induced by ethanol may result in changes in the activity of membrane-bound enzymes that have been shown to require a specific membrane fluidity and composition for optimal function. In this study we have carried out the analysis of the effects of ethanol on the different enzyme activities of hepatic microsomes and mitochondria. Our results show that chronic ethanol treatment causes marked changes to enzyme activity in the mitochondrial and microsomal electron-transport systems in chick liver. The inhibition observed in the mitochondrial enzyme activities studied, indicates that ethanol ingestion depresses the functionality of the respiratory-chain. In microsomes, NADH cytochrome c reductase activity was significantly decreased whilst NADH cytochrome b 5 reductase activity was increased after ethanol administration. Hepatic mitochondria and microsomes from control and chronic ethanol-treated chicks were submitted to ethanol in vitro in order to study the possible existence of adaptive changes in the different enzyme systems as consequence of long-term ethanol administration. Incubation of control membranes with different amounts of ethanol induced marked alterations in enzyme activities. In membranes isolated from ethanol-treated chicks, ethanol also produced a similar effect except with cytochrome oxidase and NADH cytochrome b 5 reductase, which resisted alteration by ethanol added, suggesting the existence of adaptive changes in these enzyme activities that allow them to remain unaltered after exposure to ethanol in vitro.