Transplacental movement of inorganic lead in early and late gestation in the mouse.

203Pb(NO3)2 was administered i.v. to pregnant C57BL mice at different stages, from day 8 to day 18 of gestation. The whole animals or excised uteri were subjected to autoradiography or were autopsied for scintillation counting of excised organs. Lead appeared in embryonic and fetal tissues at all stages of gestation. Early (approx. day 8-11) lead was restricted mainly to the embryonic blood, suggesting that free lead was essentially not transferred to the embryo but may have been incorporated in the embryonic hemoglobin when the erythrocytes were formed in the yolk sac placenta (an extraembryonic membrane). From day 12 and later, an uptake was seen in the liver and the cartilaginous skeleton, and from day 14, a strong accumulation was found in calcified bone. This means that the overall fetal concentration increased successively with gestational age of the conceptus. The uptake in fetal liver may be related to the erythropoiesis taking place in the liver in later gestation. While an accumulation of lead was observed in proximal tubuli of the maternal kidney, no corresponding uptake occurred in the fetal kidney. Although lead is teratogenic, causing among others skeletal defects, no effect of inorganic lead in mM concentration was seen on a chondrogenic cell system in vitro. Due to the predominance of lead in hemoglobin, a mechanism of teratogensis based on inhibition of fetal hemoglobin synthesis or function is discussed.