Polychlorinated biphenyls, classified as either phenobarbital- or 3-methylcholanthrene-type inducers of cytochrome P-450, are both hepatic tumor promoters in diethylnitrosamine-initiated rats

Abstract The cytochrome P -450 isozymes, cytochrome P -450 MC 1 and MC 2 , purified from rats treated with 3-methylcholanthrene (MC), were found by immunohistochemical staining to be strongly induced in the livers of rats treated with 3,3′, 4,4′-tetrachlorobiphenyl (TCBP), while the cytochrome P -450 isozymes, PB 1 and PB 2 , purified from the livers of rats treated with phenobarbital (PB), were shown to be induced in the livers of rats treated with 2,2′, 4,4′, 5,5′-hexachlorobiphenyl (HCBP). The latter compound also strongly induced NADPH-cytochrome P -450-reductase. Following induction, all 5 enzymes were located preferentially in the centrilobular and midzonal region of the liver acinus.…