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 suspe nded 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. T he relaxation induced by substance P was inhibited by the cyclo-oxygen ase antagonist indomethacin, while the nitric oxide-synthetase inhibit or L-N-G-monomethylarginine was without effect. These findings suggest that the relaxatory effect of substance P in the human umbilical arte ry is dependent on an intact endothelium. In contrast to the case in m ost other vessels, the relaxation is not mediated via the release of e ndothelium-derived relaxing factor, but seems to be dependent on prost anoid synthesis.