Continuous infusion of 17-hydroxyprogesterone caproate into either the fetoplacental or intervillous circulation of a placental cotyledon attenuates vasoconstriction of the fetoplacental arteries by thromboxane mimetic U46619

Objective The objective of the study was to determine whether pretreatment of fetal or maternal placental vasculature with 17-hydroxyprogesterone caproate (17-P) attenuates the vasoactive effect of the thromboxane mimetic U46619. Study Design Two cotyledons were obtained from each placenta studied. For the first 5 placentas, the fetal artery of 1 cotyledon from each pair was infused with 17-P. After 30 minutes, a bolus dose of U46619 was administered to both cotyledons. An identical procedure was carried out on the next 5 placentas except that 17-P was infused into the intervillous space. Results The pressure excursion caused by bolus administration of U46619 was less in the cotyledons infused with 17-P, both in the 5 cases in which the fetal vasculature was infused with 17-P ( P = .0035) and in the 5 cases in which the maternal vasculature was infused with 17-P ( P = .038). Conclusion Pretreatment of either the fetal or maternal circuits of the placenta with 17-P attenuates U46619-mediated fetoplacental vasoconstriction.