Enzyme induction by o-xylene inhalation.

Inhalation of 4500 mg o-xylene by rats was found to produce adaptational and pathologic changes in the liver by the end of the 1st week, reflected in an increase in relative liver weight, shortening of the hexobarbital sleeping time, an increase in the concentration of cytochrome P-450, with a decrease in the activities of aniline hydroxylase and of aminopyrine N-demethylase. Six weeks after the start of inhalations all the changes in the liver and in the mixed function oxydase system (MFO) were of an adaptational pattern characterized by an increase in relative liver weight as well as in cytochrome P-450 and b5 concentrations, a shortening of the hexobarbital sleeping time and an increase in the activity of aniline hydroxylase and of aminopyrine N-demethylase.