Promotion by polychlorinated biphenyls of enzyme-altered foci in rat liver.

Aroclor 1254 is a complex mixture of polychlorinated biphenyls (PCB) that upon prolonged administration has been reported to produce hepatic tumors in mice and rats. The ability of Aroclor 1254 to promote enzyme-altered foci was determined in an initiation/promotion bioassay in rat liver. Initiation was accomplished in rats that received a 2/3 partial hepatectomy followed in 24 h by diethylnitrosamine (DENA). Aroclor 1254 was administered to each rat 7, 28 and 49 days after the DENA and some of the rats were killed 21 days after each dose of Aroclor. The liver of rats that received Aroclor 1254 on either day 7 or on day 7 and 28 contained an increased incidence of gamma-glutamyltranspeptidase (GGTase)-positive foci compared to partial hepatectomized and DENA treated rats given tricaprylin (the solvent for Aroclor 1254). Therefore, Aroclor 1254 was demonstrated to enhance the appearance of enzyme-altered foci after only a single oral dose.