NO IS MORE IMPORTANT THAN PGI(2) IN MAINTAINING LOW VASCULAR TONE IN FETOPLACENTAL VESSELS

The endothelial cells of the human umbilical artery and vein release t he vasodilators prostacyclin [prostaglandin (PG) 121 and nitric oxide (NO). However, the role of these two substances in the maintenance of vasodilator tone in the fetoplacental circulation is not known. Studie s were therefore undertaken to compare the relative release of PGI2 an d NO from perfused segments (10 cm) of endothelium-intact human umbili cal artery (HUA) and vein (HUV) utilizing the cascade bioassay The end othelium-denuded bovine pulmonary arterial strip was used as the detec tor tissue because this tissue relaxes equally to various concentratio ns of PGI2 and S-nitroso-N-acetylpenicillimine (SNAP), which acte by r eleasing NO. The basal release of NO from the HUA was approximately fi ve times greater than that of PGI2. After stimulation with A-23187, th e release of NO from HUV was five to six times greater, and from the H UA, the release was three times greater compared with the PGI2. SNAP w as significantly more potent compared with PGI2 in relaxing endotheliu m-denuded rings of human umbilical and chorionic plate arteries in vit ro. These studies suggest that NO is more important than PGI2 for main tenance of low vascular tone in feto-placental vessels, because there is a greater release of NO from the HUA and HUV, and NO is more potent in relaxing endothelium-denuded feto-placental vessels in vitro relat ive to PGI2.