Relative liver tumor promoting activity of some polychlorinated dibenzo-p-dioxin-, dibenzofuran- and biphenyl-congeners in female rats

Abstract Some pentachlorinated dibenzo- p -dioxin-, dibenzofuran- and biphenyl-congeners and TCDD were studied for liver tumor promoting activity in a medium-term altered foci assay with nitrosamine initiated female SD rats. The congeners under study were administered by weekly subcutaneous injections for 20 weeks. Evaluation of GGT + or GST-P + altered foci development showed that all congeners studied acted as promoters of hepatocarcinogenesis. TCDD and 1,2,3,7,8-pentachloro-dibenzo- p -dioxin (PeCDD) were virtually equipotent as enhancers of foci development while 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) displayed approximately 10% of the activity of the dioxins. The PCB congener 2,3,3′,4,4′-pentachlorobiphenyl (PCB105) also enhanced foci development but was more than 1000 times less potent than TCDD. Analysis of the dioxin- and furan-congeners by GC/MS-technique showed that the retention of PeCDD and PeCDF in liver tissue was approximately 7 and 20 times, respectively, as high as the retention of TCDD.