RELATIVE TUMOR-PROMOTING ACTIVITY OF 3 POLYCHLORINATED-BIPHENYLS IN RAT-LIVER

The relative tumour promoting activity of three structurally and toxic ologically diverse polychlorinated biphenyls (3,4,5,3',4'-penta-,2,3,4 ,3',4'-penta- and 2,4,5,2',4',5'-hexachlorobiphenyl) was measured in a n initiation/promotion assay in nitrosodiethylamine-initiated female S prague-Dawley rats. The congeners under study were administered by onc e-weekly subcutaneous injections for 20 weeks. Evaluation of the devel opment of gamma-glutamyl transpeptidase (GGT)- and glutation transfera se 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-positiv e tissue in the 3,4,5,3',4'-pentachlorobiphenyl-treated animals (100 m ug7kg per week) was 23%, while the volume fractions of altered liver t issue in the rats treated with 2,3,4,3',4'-pentachlorobiphenyl (5000 m ug/kg per week) and 2,4,5,2',4',5'-hexaCB (20,000 mug/kg per week) wer e 1.2 and 2.3, respectively. The enhancement of GGT- and GST-P-positiv e foci was accompanied by an increased incidence of histological chang es in the livers.