Endothelium-dependent relaxation to substance P in human umbilical artery is mediated via prostanoid synthesis.

To investigate the relaxatory effect and mode of action of substance P in the human umbilical artery, ring segments of the artery were suspended in organ baths to record the circular motor activity. Substance P induced a significant relaxation in segments with intact endothelium pre-contracted by potassium or 5-hydroxytryptamine. Segments devoid of their endothelium failed to relax when challenged with substance P. The relaxation induced by substance P was inhibited by the cyclo-oxygenase antagonist indomethacin, while the nitric oxide-synthetase inhibitor L-NG-monomethyl-arginine was without effect. These findings suggest that the relaxatory effect of substance P in the human umbilical artery is dependent on an intact endothelium. In contrast to the case in most other vessels, the relaxation is not mediated via the release of endothelium-derived relaxing factor, but seems to be dependent on prostanoid synthesis.