Transferrin receptor expression in the human placenta.

Iron transport from the mother to the fetus is mediated by transferrin receptors located at the maternofetal interface of the placenta. Transferrin receptors bind iron-loaded transferrin molecules from the maternal plasma, thus allowing iron uptake by trophoblastic cells which then deliver the metal to the fetal plasma. We have measured the transferrin receptor content in the placentas from 16 normal-term pregnancies and investigated the relationships between transferrin receptor expression and non-haem iron content, as well as maternal and fetal iron status. Transferrin receptor content was evaluated indirectly by determining the transferrin binding capacity of a placenta extract. Transferrin receptor content of the placenta ranged from 20 to 154 micrograms/g of tissue, with a mean value of 96 +/- 37 micrograms/g. The mean non-haem iron content was 78 +/- 11 micrograms/g of tissue, corresponding to 47 +/- 10 mg for the whole placentas. The amount of transferrin receptors in the placenta was found to be inversely related to the amount of non-haem iron (r = 0.64; p less than 0.025). No significant relationship was observed between each of these two parameters and the iron status of either the mother or the fetus. We conclude that placental non-haem iron, which represents a storage form of this element, is likely to play a regulatory role in the expression of transferrin receptors, and consequently in the process of iron uptake by the placenta.