Inhibitory Effect of Polychlorinated Biphenyls on Liver Tumorigenesis in Rats Treated With 3′-Methyl-4-dimethylaminoazobenzene, N-2-Fluorenylacetamide, and Diethylnitrosamine2

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Abstract
Studied were the effects of polychlorinated biphenyls (PCB) on liver carcinogenesis in rats treated with the hepatic carcinogens 3′methyl-4-dimethylaminoazobenzene (3′-Me-DAB), N-2-fluorenylacetamide (2FAA), and/or diethylnitrosamine (DEN). Animals were examined histopathologically after they had received the experimental diet for 20 weeks and then the stock diet for 4 weeks. Liver tumors developed in 65.2, 53.8, and 92.3% of rats in groups treated with 0.03% 3′-Me-DAB, 0.015% 2-FAA, and 0.0025% DEN, respectively. Rats that received 0.05% PCB only did not develop liver tumors, and those treated with PCB and the carcinogens developed only a few tumors. Multiple liver tumors developed after treatment with 0.03% 3'-Me-DAB plus 0.0025% DEN (92.3% incidence) and 0.015% 2-FAA plus 0.0025% DEN (81.8%); after treatment with these combinations plus PCB, the incidence of liver tumors was very low or zero. Histologic examination showed that PCB also inhibited development of nodular hyperplasias, oval cell infiltration, and bile duct proliferation induced in the liver by the chemical carcinogens.

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