Imamura_1984_Pestic.Biochem.Physiol_22_312

The inhibitory effects on liver microsomal carboxylesterases and erythrocyte membrane esterases produced by an impurity of malathion was investigated. Treatment of rats with an impurity of malathion, O,O,S-trimethyl phosphorothioate (OOS-Me), and its structural analog O,O-dimethyl S-ethyl phosphorothioate (OOS-Et) inhibited liver microsomal malathion and phenthoate carboxylesterases. The inhibition lasted for at least 7 days following a single oral administration of OOS-Me. These treatments inhibited acetylcholinesterase (AChE) and (Na+ + K+)-dependent ATPase of erythrocyte membranes which persisted at least 3 days. OOS-Et was a more potent inhibitor of all the esterases examined than OOS-Me. Pretreatment of rats with a metabolic inducer, phenobarbital, or a metabolic inhibitor, piperonyl butoxide, had no effect on such inhibitory effects on liver microsomal carboxylesterases produced by OOS-Me or OOS-Et.