The effect of combined exposures to ethanol and xylene on rat hepatic microsomal monooxygenase activities.

Studies on rats treated for 8 months with ethanol (10% solution in drinking water) and simultaneously exposed to xylene vapour (12,000 mg/m3, 5 hr daily) for the last 9 days revealed that the chemicals exert additive stimulatory effect on hepatic microsomal monooxygenase: the activity of aniline p-hydroxylase increased by 380%, microsomal ethanol oxidizing system by 92%, NADPH-cyt. c reductase by 30% and the level of cytochrome P-450 by 70%. The changes were accompanied by a marked proliferation of smooth endoplasmic reticulum (a subcellular site of cytochrome P-450 monooxygenases in the hepatocytes) and an increased NADPH-Fe2+- and ascorbate-Fe2+-driven lipid peroxidation in microsomal membranes--a potential toxic mechanism. Interaction of ethanol and xylene with cytochrome P-450 monooxygenases may enhance metabolic capacity of the liver and in consequence modify biological/toxic effects of occupational exposure to solvents in the case of alcohol abuse.