Enzyme induction by repeated administration of tetrachlorvinphos in rats

The capability of enzyme induction in male rats was studied following the administration of tetrachlorvinphos (TCVP). A single oral dose of either 250 or 1000 mg/kg caused a more marked inhibition of true (erythrocyte) ChE than of pseudo (serum) and brain ChE activities. Dose-related increases in the activities of two hepatic microsomal enzyme activities, aminopyrine demethylase and EPN (o-ethyl O-p-nitro-phenyl phenylphosphonothioate) detoxification enzyme, were observed after 10 days of successive administration of TCVP at doses of 60 and 250 mg/kg, po. The liver to body weight ratio of rats increased on the first 7 days and then decreased on Day 10. The repeated administration of TCVP induced the enzymes responsible for the metabolism of TCVP up to 7-fold in microsomes and 1.2-fold in the supernatant fraction. The results demonstrate that the repeated application of TCVP as an insecticide may decrease its toxicity by its capacity to induce metabolizing enzymes.