VASCULAR REACTIVITY TO ENDOTHELIUM-DERIVED RELAXING FACTOR IN HUMAN UMBILICAL ARTERY AT TERM PREGNANCY

It has been reported that human umbilical artery (HUA) at term pregnan cy released endothelium-derived relaxing factor (EDRF), using a superf usion bioassay system. However, other reports showed that endothelium- dependent relaxation was not observed in isometric tension studies usi ng HUA ring with intact endothelium. Thus, we intended to clarify whet her vascular smooth muscle of HUA at term is sensitive to EDRF. HUA wa s obtained after normal vaginal delivery or cesarean section at term. Isometric tension studies were performed in normal Krebs solution, usi ng HUA rings or ships, which were prepared in calcium-free Krebs solut ion. Sodium nitroprusside (SNP), a nitric oxide (NO) donor drug, relax ed HUA rings precontracted with 0.1 mu M 5-hydroxytryptamine (5HT) in a dose-dependent manner(1 nM - 10 mu M). Histamine, substance P, carba chol, or the calcium ionophore A23187, which are considered to be EDRF -releasing agents, did not relax the HUA rings. By immunohistochemical study, it was confirmed that endothelial cells were present in the lu minal surface of the HUA rings after the isometric tension recording. In a co-axial bioassay system involving HUA strips denuded of endothel ium and rabbit aorta with intact endothelium, HUA strips precontracted with 0.1 mu M 5HT were relaxed in response to 1 mu M SNP but not 1 mu M carbachol, which released EDRF from the endothelium of rabbit aorta . These findings suggest that HUA at term is sensitive to NO but not E DRF.