Numerical density of nuclei in the sheep placenta.

A method is described for estimating the number of nuclei of different cell types in the sheep placenta. The method was applied to the study of six placentas of different ages and the results have been correlated with data on the chemical composition and the physiology of the ovine placenta. In agreement with studies of placental DNA content, there is no demonstrable increase in the total number of placental nuclei in the last two months of gestation. However, the number of fetal mesenchymal nuclei decreases and there is a concomitant increase of fetal endothelial nuclei from 80 days to term. These changes correlate with a decrease in volume of the core of the placental villi and increase in umbilical blood flow.