Effect of polybrominated biphenyls on the accumulation of DNA, RNA, and protein in cultured rat embryos following maternal administration.

Using a system of whole-embryo culture, the effect of polybrominated biphenyls (PBB) was investigated on the rates of DNA, RNA, and protein accumulation in rat embryos. Embryos were isolated on the 10th gestational day (sperm day = Day 0) either 4 or 24 hr after maternal administration. The cultivation period was for 24 or 42 hr. DNA, RNA, and protein accumulation rates were not affected by a 4-hr previous maternal administration either at the beginning or following cultivation. At the beginning of cultivation for embryos exposed to PBB 24 hr before dissection, there was a significant reduction in DNA and total embryonic protein but RNA values were not affected. At 24 hr cultivation, protein values were no longer significantly different. DNA values remained significantly lower throughout culture. The significant anatomical differences noted at 24 hr cultivation were: (i) a failure of neuropore closure; (ii) a retention of a dorsiflexed position; (iii) a retardation in somite development; (iv) a reduced number with anterior limb buds present; (v) a reduction in the number establishing a visceral yolk sac circulation; and (vi) a decreased heart rate. After 42 hr in culture, the only significant anatomical differences were a reduction in the number of embryos developing anterior limb buds and a decrease in the number of somites added. It is concluded that the major embryonic effects of PBB for the first 24 hr after administration appear to be transitory if the embryo is removed from the exposure environment.