Movement of Calcium in Both Directions Across the Primate Placenta. ∗

Abstract

Summary

Transfer of Ca from mother to fetus concurrent with transfer from fetus to mother was studied in 3 pregnant rhesus monkeys. Ca⁴⁵ was injected into a fetal inter-placental vessel simultaneously with intravenous injection of Ca⁴⁷ into the anesthetized mother. Samples of maternal blood (MB), fetal blood (FB), and amniotic fluid (AF) were assayed for Ca⁴⁵, Ca⁴⁷ and non-radioactive Ca. Initial loss of Ca⁴⁷ from MB was matched by rapid initial appearance in FB (t 1/2 ≤ 6 min) and somewhat slower entry into AF. Similarly, Ca⁴⁵ appeared in MB at a rate almost equal to the initial rate of loss from FB. The quantity of Ca crossing the placenta daily was at least 6–10 times that required for fetal skeletal growth.