Transfer of radioactive iron via the placenta and accessory fetal membranes in the rabbit

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

The distribution of radioactivity in the fetus and placental structures was studied at different stages of gestation in the rabbit following the intravenous injection of radioactive iron as Fe⁵⁹ sulphate. The following general results were obtained: a) A steady increase in the uptake of radioiron by the fetus and fetal placenta took place with advancing gestation. The rate of uptake showed a sharp increase at about the 20th day. b) The rate of iron transport across the placenta increased during gestation, especially in the last third of pregnancy. c) Radioiron was concentrated in the yolk sac in the early stages and in the fetal liver in the later stages of gestation. No change in the pattern of accumulation of radioiron by the fetus took place when the vessels of the yolk sac were ligated before injection. These results suggest that the yolk sac has no role in iron transport and that early in gestation it may carry on some of the functions of the fetal liver with respect to iron. d) Alternative sites of transport for iron were investigated by the injection of radioiron into the uterine cavity. The results indicate that if iron gains access to the uterine cavity, e.g. via the uterine mucosa or via the chorion and periplacental decidua, it is rapidly absorbed by the yolk sac and enters the fetus. However, such a pathway for iron transfer to the fetus does not seem to be important physiologically.