Comparison of the effect of an equimolar and low dose of fenitrothion and methylparathion on their own metabolism in rat liver.

The effects of fenitrothion and methylparathion on the activities of cholinesterase and hepatic microsomal monooxygenases were investigated and compared following a single or repeated oral administration of an equimolar and low dose of the insecticides. The activities of cholinesterase in brain and plasma were inhibited equally by the repetitive administration of both insecticides. Aminopyrine N-demethylase activity and cyt.P-450 content were not affected under the same experimental conditions. However, methylparathion, when given repeatedly, inhibited the dearylation and desulfuration of it own. The results may indicate that low dose continuous exposure to methylparathion could cause the depression of its own metabolism in rat.