Effects of ethanol administration on rat liver plasma membrane-bound enzymes

Changes in the properties of rat liver plasma membranes were examined in studies designed to differentiate between direct and metabolic effects of acute and chronic ethanol ingestion. One hour after a single dose of ethanol (3 g/kg body weight) there were increases in Na+,K+-ATPase (32%) and 5'-nucleotidase (36%), and hepatic concentrations of ethanol and acetaldehyde were approximately 23 mM and 50 microM, respectively. Na+,K+-ATPase and 5'-nucleotidase activities in liver plasma membranes from control rats were not significantly changed by in vitro addition of 30 microM acetaldehyde or 50 mM ethanol. Increases in Na+,K+-ATPase (approximately 20%) and 5'-nucleotidase (approximately 30%) were also observed in liver plasma membranes isolated from rats 16 hr after feeding ethanol or sucrose supplements for 17 days. The intake of calories from dietary protein and lipid was decreased by about 25% in both the ethanol and sucrose-fed animals. Na+,K+-ATPase activities in liver plasma membranes isolated from control rats were inhibited (approximately 20%) by 100 mM ethanol in vitro, whereas no inhibition was observed using membrane preparations from rats fed ethanol or sucrose supplements. Our results show that changes in liver plasma membrane enzyme activities associated with a single dose of ethanol are not a direct effect correlated with blood, hepatic or plasma membrane concentrations of ethanol or acetaldehyde. Chronic ingestion of ethanol or sucrose supplements had similar effects on liver plasma membrane enzyme characteristics and parallel changes in nutrient intake may be a more feasible explanation of these results than any analogous direct effects of the two compounds.