Relative tumour promoting activity of three polychlorinated biphenyls in rat liver.

Abstract The relative tumour promoting activity of three structurally and toxicologically diverse polychlorinated biphenyls (3,4,5,3′,4′-penta-,2,3,4,3′,4′-penta- a and 2,4,5,2′,4′,5′-hexachlorobiphenyl) was measured in an initiation/promotion assay in nitrosodiethylamine-initiated female Sprague-Dawley rats. The congeners under study were administered by once-weekly subcutaneous injections for 20 weeks. Evaluation of the development of γ-glutamyl transpeptidase (GGT)- and glutation transferase P (GST-P)-positive hepatic foci showed that all congeners promoted altered hepatic foci, although 3,4,5,3′,4′-pentachlorobiphenyl was far more potent. The volume fraction of the liver occupied by GGT-positive tissue in the 3,4,5,3′,4′-pentachlorobiphenyl-treated animals (100 μg7kg per week) was 23%, while the volume fractions of altered liver tissue in the rats treated with 2,3,4,3′,4′-pentachlorobiphenyl (5000 μg/kg per week) and 2,4,5,2′,4′,5′-hexaCB (20,000 μg/kg per week) were 1.2 and 2.3, respectively. The enhancement of GGT- and GST-P-positive foci was accompanied by an increased incidence of histological changes in the livers.