Administration of 2,3,7,8-TCDD (20 g/kg) to female C57BL/6 mice gave >60% cleft palate in the litters. Previous studies have shown that cotreatment of the pregnant mice with 2,3,7,8-TCDD (20 g/kg) and Aroclor 1254 (750 mol/kg) resulted in complete protection of the animals from cleft palate. In contrast, a lower dose of Aroclor 1254 (250 mol/kg) was a less effective 2,3,7,8-TCDD antagonist. Several PCB congeners, including 2,2,5,5-tetrachlorobiphenyl and 2,2,4,4,5,5-hexachlorobiphenyl, which exhibit some Ah receptor binding activity were investigated as 2,3,7,8-TCDD antagonists in the in vivo teratogenicity assay system. Both PCB congeners significantly protected the mice from 2,3,7,8-TCDD-mediated cleft palate. The significance of these results and their mechanistic implications will be discussed. 1989.
