Reactivity of human placental chorionic plate vessels is modified by level of oxygenation: differences between arteries and veins.

Normal fetal development in utero is dependent upon adequate perfusion of the placental vasculature, yet how fetoplacental blood flow is matched to maternal blood flow is unknown. In the perfused placental cotyledon in vitro, reduced oxygenation promotes vasoconstriction, which may act to direct blood in fetoplacental vessels to effectively perfused regions of the intervillus space. We aimed to demonstrate that oxygen tension could directly modify placental chorionic plate vessel vasoreactivity. Small arteries and veins from the chorionic plate were dissected from biopsies from term placentae of uncomplicated pregnancies and studied using parallel wire myography. Chorionic artery and vein vasoconstriction in 20%, 7% and 2% oxygen was assessed utilizing the thromboxane-mimetic U46619. Reduced oxygenation increased arterial maximal active effective pressure production and sensitivity to U46619. This effect was cyclo-oxygenase independent. In veins, modified oxygenation did not alter vasoconstriction. Vasodilatation in response to the NO donor sodium nitroprusside was increased in lowered oxygenation in veins but not in arteries. We suggest that modified oxygenation may play a role in the control of the blood flow in the fetoplacental circulation.