THE ABILITY TO ALTER THE GAP JUNCTION PROTEIN EXPRESSION OUTSIDE GST-P POSITIVE FOCI IN LIVER OF RATS WAS ASSOCIATED TO THE TUMOR PROMOTIONPOTENCY OF DIFFERENT POLYCHLORINATED-BIPHENYLS

The results demonstrate different modes of action by a dioxin-like pol ychlorinated biphenyl (PCB 126) and a non dioxin-like PCB (PCB 153) in the alteration of connexin (ex) 26 and ex 32 expression outside GST-P positive foci in liver of female Sprague-Dawley rats, treated accordi ng to an initiation-promotion protocol. A decreased relative amount of immunopositive ex 26 and ex 32 spots in the parenchymal cell plasma m embranes was observed after treatment with the potent tumour promoters PCB 126 or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). No reduction o f ex 26 or ex 32 was noted after administration with the weaker tumour promoters PCB 153 or PCB 118 (PCB 118; both dioxin- and non dioxin-li ke). Additionally, we found that the down-regulation of connexins also occurred in rats treated with PCB 126 or TCDD without partial hepatec tomy and initiation with nitrosodiethylamine. In summary, the results indicate that the ability to reduce the gap junction protein level in liver of rats can be associated to the tumour promotive potency of the different PCB-congeners and TCDD. (C) 1997 Elsevier Science Ireland L td.