Contrasting effects of ethylenethiourea on hepatic monooxygenases in rats and mice

The effects of ethylenethiourea (ETU) on the hepatic xenobiotic metabolizing system in rats and mice were investigated. Male rats and male mice were given oral doses of 50 and 75, or 50, 75, 100, 500, and 1,000 mg/kg for 3 days. The microsomal enzymes studied were aminopyrine N-demethylase, aniline hydroxylase, and cytochrome P-450. In rats, the activity of aminopyrine N-demethylase was reduced to values between 60 and 70% of controls 24 h after treatment. A decrease in aniline hydroxylase activity and cytochrome P-450 content was observed on the 3rd day after exposure. In mice, treatment with ETU resulted in an increase of cytochrome P-450 at all dose levels. The activity of aniline hydroxylase was significantly elevated in the groups receiving doses of 100 mg/kg and higher. Aminopyrine N-demethylase was unaffected by the treatment. The results suggest that there are qualitative differences between rats and mice after ETU exposure with respect to the response of the hepatic mono-oxygenases.