Effects of methylbenzenes on microsomal enzymes in rat liver, kidney and lung

The effects of pretreatment with toluene, o-, m-, p-xylene and mesitylene were investigated on the microsomal enzymes of liver, kidney and lung in rats. The activities of aminopyrine N-demethylase, aryl hydrocarbon hydroxylase, aniline hydroxylase, NADPH-cytochrome c reductase, as well as the concentrations of cytochrome P-450 and cytochrome b5 were determined. The effects were most marked in the liver, where toluene caused increase in aniline hydroxylase and cytochrome P-450; o-xylene in aminopyrine N-demethylase and cytochrome b5; m-xylene and mesitylene in all the enzymes investigated. In kidneys, all the compounds increased the activity of aniline hydroxylase; m-xylene induced cytochrome P-450 and b5 as well as NADPH-cytochrome c reductase; p-xylene induced cytochrome P-450, and mesitylene cytochrome P-450 and b5. Aminopyrine N-demethylase activity was decreased by toluene. In lungs, only mesitylene caused any significant differences from the controls: increase in aminopyrine N-demethylase and aryl hydrocarbon hydroxylase, decrease in aniline hydroxylase. The methylbenzenes tested induced the microsomal enzymes in a rough correlation to the number of their methyl groups and their hydrophobic properties.