Effects of polychlorinated biphenyls in rat liver: quantitative analysis of enzyme-altered foci.

The promotional effect of various polychlorinated biphenyls and phenobarbital on enzyme-altered lesions in the rat liver was quantified within the framework of the two-stage carcinogenesis model of Moolgavkar and colleagues. The experiment analyzed here followed an initiation-promotion protocol in which female Wistar rats were initiated with diethylnitrosamine (DEN) at 10 mg/kg body wt for 10 days followed by a 8-week period of promoter treatment with various cytochrome P450 isoenzyme inducing and noninducing compounds. This analysis included 4-monochlorobiphenyl, 2,2',4,5'-tetrachlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl and 3-methylcholanthrene, all administered at 150 mumol/kg body wt, and phenobarbital which was administered continuously in the diet at 0.05% until termination. Animals were killed either 1 or 9 weeks after the end of treatment and their livers were examined for enzyme histological alterations. Focal transections were classified as falling into three phenotypic categories: ATPase dominant, GGT dominant, or ATPase plus GGT (coextensive). A quantitative method was used to analyze the data consisting of the number and sizes of the focal transections. The number of cells altered by the DEN treatment and cell kinetic parameters measuring the promotional effect of the various compounds were estimated. On the basis of these estimates, we computed the number of nonextinct altered foci and their volume fraction as functions of time. We found that foci exhibiting the coextensive phenotype respond most efficiently to promoter treatment, while GGT dominant foci respond weakly to all the promoters with the exception of 3-MC. For phenobarbital, we observed a significant slowing of focal cell proliferation over time.