Benzo[a]pyrene initiates enzyme-altered islands in the liver of adult rats following single pretreatment and promotion with polychlorinated biphenyls.

Treatment of adult female rats with a single dose of benzo[a]pyrene (BaP) fails to initiate preneoplastic enzyme-altered islands in their livers. Treatment with polychlorinated biphenyls (PCBs) at a dose which strongly induces aryl hydrocarbon(BaP)hydroxylase prior to BaP application and followed by promotion with PCBs causes the appearance of about 9 adenosine-5'-triphosphatase-deficient and 7 gamma-glutamyltranspeptidase-positive islands/cm2 after 12 weeks. PCB-pretreatment or promotion alone did not increase the BaP-dependent formation of islands above that of the PCB-treated controls (2-3 islands/cm2). The results suggest that upon alteration of its metabolism BaP causes the formation of preneoplastic lesions in the liver which become manifest by promotion.