Trichloroethylene effects on the formation of enzyme-altered foci in rat liver.

The initiating and promoting effects of trichloroethylene in rat liver were investigated using the enzyme-altered foci bioassay. The incidence of gamma-glutamyl transpeptidase (GGT)-positive foci was used as an early histochemical marker of putative preneoplastic hepatocytes. A single PO dose of trichloroethylene (490 mg/kg) was administered in corn oil to rats which had been partially hepatectomized 24 h previously. Three days following gavage with the chlorinated hydrocarbon the rats were promoted with an 8-week regimen of 500 ppm phenobarbital in drinking water. This protocol is known to induce enzyme-altered foci in the livers of animals which have received an initiating dose of a genotoxic carcinogen. Trichloroethylene was not found to induce GGT-positive foci under these conditions. Additionally, groups of rats were partially hepatectomized, initiated with N-nitrosodiethylamine (30 mg/kg; PO) and administered five times weekly doses of 200 mg trichloroethylene per rat in order to investigate the promoting activity of the chlorinated hydrocarbon in rat liver. No significant promoter effects were observed with trichloroethylene, although the results in this case were somewhat equivocal. The findings of these investigations are taken as partially supportive of an epigenetic, cytotoxic mechanism of tumorigenic action of trichloroethylene.