Effects of indomethacin on contractility of isolated human umbilical artery

Contractions of isolated strips of human umbilical artery (HUA) induced by arachidonic acid were antagonized by indomethacin at concentrations as low as 1 microgram/ml. Much higher concentrations (25 and 65 microgram/ml) were needed to relax KCl-contracted strips of HUA. These data suggest that indomethacin at 1 microgram/ml inhibits endogenous synthesis of vasoconstrictive prostaglandin-like substances whereas indomethacin at higher concentrations causes nonspecific relaxation. Contractions induced by 5-hydroxytryptamine (5-HT), KCl and prostaglandin F2 alpha (PGF2 alpha) were antagonized by indomethacin at 25 and 65 microgram/ml, but not at 2.5 microgram/ml. These data suggest that the contractile responses to 5-HT, KCl and PGF2 alpha are not mediated by endogenous prostaglandin-like substances. Contractions induced by adenosine triphosphate (ATP), in contrast, were completely inhibited by indomethacin (1 microgram/ml). Therefore, the data suggest that prostaglandin-like substances may mediate contractions to ATP.