Failure of parathyroid hormone to cross the nonhuman primate placenta.

Following infusion of parathyroid extract (PTE), parathyroid hormone (PTH) did not cross the placenta from the monkey mother to her fetus. Although maternal PTH levels increased four- to 12-fold, fetal PTH levels remained at the base line at all times tested. To determine if PTH crossed the placenta from fetus to mother, PTE was infused into the fetal aorta while the monkey baby remained in utero. PTH in the fetal serum increased ten-fold without a significant change in maternal serum PTH. Thus, PTH does not cross the placenta in either direction. Blood ionized calcium levels in nonpregnant female monkeys, following infusions of ethylenediaminetetra-acetate (EDTA) were shown to decrease, with a subsequent increase in blood PTH levels. Thus, the monkey arathyroid gland was shown to be physiologically responsive to lowered calcium levels. Biological half-life disappearance times of beef PTH in monkey fetuses and their mothers were similar to those found in human beings.