The hepatotoxicity of O,O-diethyl, O-phenyl phosphorothionate (SV1) for the rat

The parathion analogue O, O-diethyl, O-phenyl phosphorothionate (SV1) is hepatotoxic when given in large intraperitoneal doses (400 mg/kg body weight) to male rats that have been treated previously with phenobarbitone. The lesion produced at 24 h after dosing is a periacinar hydropic degeneration which appears identical to that caused by carbon disulphide (CS2) in similarly pretreated rats. Both lesions are characterized by a marked depression in hepatic microsomal cytochrome P-450 levels, no change in the concentrations of Na+, K+ and Ca++ in liver water, in contrast to the periacinar necrogenic lesion caused by tccl4 in which Na+ and Ca++ levels markedly increase while that of K+ decreases. The similarity of the SV1 and CS2 induced liver changes, the fact that both chemicals undergo a similar oxidative desulphuration in the liver microsomes and that prior induction of the latter enzymes is necessary in order to produce the injury suggest a similar mechanism for both lesions. A reactive form of sulphur released from the metabolism of CS2 and phosphorothionates in the liver may become covalently bound to constituents of the endoplasmic reticulum of the liver cell and in this way initiate the toxic liver changes. Drugs and chemicals which contain P=S or C=S bonds and which undergo oxidative desulphuration in the liver could thus be similarly hepatotoxic.