Stage-specific effects of defined mixtures of polychlorinated biphenyls onin vitro development of rabbit preimplantation embryos

PCBs adversely affect various reproductive functions. Little is known about the embryotoxic effects during the preimplantation period in mammals. In t he present study the effects of various mixtures of highly purified PCB-con geners on embryo morphology, blastocyst formation, embryo size and cell pro liferation were investigated. For 24 hr, day 3 morulae and day 4 blastocyst s were cultured in the presence/absence of coplanar congeners (PCB77, PCB12 6, and PCB169), noncoplanar congeners (PCB28, PCB52,PCB101,PCB118,PCB138,PC B153,PCB180 or both mixtures in concentrations ranging from 0.3 ng/mL to 60 mu g/mL total PCB. The main effects were (1) degeneration of all embryos a t 60 mu g/mL, (2) reduction of cell proliferation in day 4 embryos only by coplanar PCB; in day 3 embryos, however, by all PCB-mixtures, and (3) reduc tion of cell proliferation in a non-linear dose response with the strongest impairment caused by the lowest concentration. Cell proliferation was decr eased by 0.3 ng/mL coplanar PCB to 50% of the level in control blastocysts. Our results show that purified PCB congeners in the range of 0.3 ng/mL to 30 mu g/mL affect the development of preimplantation embryos in a stage-spe cific and congener-specific manner. This study provides first evidence for an embryotoxic potential of coplanar PCB congeners. (C) 1999 Wiley-Liss, In c.