Histopathologic Studies on Liver Tumorigenesis Induced in Mice by Technical Polychlorinated Biphenyls and Its Promoting Effect on Liver Tumors Induced by Benzene Hexachloride 2
The effects of technical polychlorinated biphenyls (PCBs) on mouse liver were examined histologically and ultrastructurally. Pathologic studies were also made on the effects of PCBs on tumorigenesis induced by benzene hexachloride (BHC) in mouse liver. Neoplastic changes were observed in livers of mice fed a basal diet containing 500 parts per million (ppm) of the PCBs, Kanechlor 500, for 32 weeks. Amyloid degeneration in the liver of mice wasobserved in groups fed a diet containing lower concentrations of PCBs. Histologically and ultrastructurally, the neoplastic areas of mouse liver induced by PCBs appeared to be typical nodular hyperplasias and well-differentiated hepatocellular carcinomas. The effects of PCBson neoplastic changes induced by isomers of BHC in the livers of mice fed a diet containing BHC with or without PCBs for 24 weeks were studied. Among groups fed BHC alone, only the group receiving 250 ppm of the α-isomer developed nodular hyperplasia and hepatocellular carcinoma. However, among the groups fed BHC plus PCBs, only those receiving 100 or 50 ppm of α-BHC or 250 or 100 ppm of β-BHC developed nodular hyperplasia and hepatocellular carcinoma. Groups fed γ-BHC with or without PCBs did not show neoplastic changes of the liver. Thus PCBsthemselves induced hepatic neoplasms in mice and also promoted the induction of tumors by α-BHC and β-BHC.