Transfer of zinc⁶⁵ across the placenta and fetal membranes of the rabbit

¹ Department of Anatomy, Washington University Medical School, St. Louis, Missouri

The distribution of radioactivity in the fetus and placental structures (fetal placenta, decidua, yolk sac) has been studied at different stages of gestation following the intravenous injection of Zn⁶⁵ into the mother. The uptake of radiozinc by the products of conception increased with advancing gestation but never exceeded 8% of the total dose given. The recovery rose sharply between the 20th and 22nd day, suggesting the maturation of a fetal acceptor organ or an increased efficiency of the placental transport mechanism. Evidence is presented that the fetal liver is mainly responsible for the increased fetal recovery in the later stages of pregnancy. In addition, the placental recovery of radioactivity following the removal of the fetuses is equal to that obtained from the combined fetuses and placentae in the control side of the uterus; this suggests that the removal of radiozinc from the maternal blood is not dependent on a fetal acceptor. The transfer of radiozinc from the maternal blood is almost entirely via the fetal placenta. The yolk sac plays an insignificant part in both the storage and transport of the metal. Retrograde transfer from the fetus to the mother has also been demonstrated.