Parathyroid hormone-related protein mRNA in avascular human amnion

Previously, we found that preproendothelin-1 mRNA is present in human avascular amnion tissue. In this investigation, we evaluated the possibility that another vasoactive protein, namely, parathyroid hormone-related protein (PTH-rP), also is produced in amnion. Using a specific cDNA probe, we identified PTH-rP mRNA in amnion tissue and found that the level of PTH-rP mRNA in placental amnion was greater than that in reflected amnion tissue obtained from the same pregnancy. PTH-rP mRNA also was demonstrable in chorion laeve and in decidua, but the levels of this mRNA in these tissues were much lower than that in amnion. By radioimmunoassay, we found that human amnion cells in primary monolayer culture secrete immunoreactive PTH-rP into the medium. Importantly, the placental amnion covers the chorionic vessels that traverse over the chorionic plate prior to branching into the cotelydons; specifically, there is no intervening tissue between placental amnion and the adventitial tissue of the chorionic vessel wall. Thus, the potential exists for the production of endothelin-1, a potent vasocontractant, and PTH-rP, a vasorelaxant, in placental amnion for export to the adventitial surface of the chorionic vessels. Moreover, amnion cells respond to a number of agents (e.g., transforming growth factor-beta) that effect changes in the expression of these two peptides. Therefore, the possibility should be considered that amnion-derived vasoactive proteins may modulate fetal chorionic, umbilical, and villous vessel tone and thereby fetal-placental blood flow.