Effect of methadone addiction on N-demethylation activity of rat liver microsomes.

Adult male rats were addicted to methadone via small dosages in their drinking water. The N-demethylation activity of microsomal mixed function oxidase in liver was determined for partially addicted (25 days of drug consumption) and fully addicted (38 days of drug consumption) rats. Compared to controls which did not receive the drug, enzyme activity expressed on a microsmal protein basis was increased in partially addicted, but not increased in fully addicted animals. Enzyme activity expressed on a liver weight basis was decreased in partially addicted animals but unchanged from contro levels in fully addicted animals. Brief (three-day) exposures to phenobarbital or high dosages of methadone led to an increase in N-demethylation activity.