THE TRANSFER OF RADIOACTIVE SODIUM ACROSS THE PLACENTA OF THE RABBIT

Abstract

The rates of placental transfer per unit wt. of placenta were measured in the rabbit from the 18th day of pregnancy until about term. There is an 11-fold increase in transfer rate per g. of placenta over this period. The placenta of the rabbit belongs to the hemochorial group. The rate of transfer of N24 across a unit of its wt. agrees closely with that of the placentae of the guinea pig and rat which also are hemochorial. The relative growth curve of the rabbit fetus is similar to the curve of rate of transfer of Na24 to a unit wt. of fetus only after the 25th day of pregnancy. Prior to this, large changes in the relative growth curve anticipate similar changes in the curve of transfer rate per unit wt. of fetus by about 4 days. Differences in the relative growth rates of guinea pig and rabbit are correlated with corresponding differenecs in the rate of transfer per unit wt. of the respective fetuses.