Radial artery graft spasm in the perioperative or postoperative period of coronary bypass surgery necessitates urgent treatment due to risk of graft failure and mortality. Herein, we evaluated the effect of iloprost, a prostacyclin (PGI(2)) analogue, against the contractions produced by noradrenaline and potassium chloride on isolated human radial artery. Following the determination of endothelial and vascular relaxing capacities of the arteries, iloprost (10(-9)M-10(-6)M) was cumulatively applied on rings precontracted submaximally with the spasmogens. In some rings, the response to iloprost was assessed following pretreatment with nitric oxide (NO) synthase inhibitor, L-NAME (3 x 10(-4)M,30 min). Iloprost produced complete relaxations on radial artery rings pre contracted with noradrenaline whereas, only moderate relaxations against the contractions induced by potassium chloride. Notably, the relaxation to iloprost was remarkably blunted in radial arteries with impaired endothelial function. Moreover, the relaxation to iloprost was unchanged in rings pretreated with L-NAME. Our results demonstrated that iloprost could be a potent relaxant agent in reversing radial artery spasm, particularly initiated by noradrenaline, possibly acting via an endothelium-mediated mechanism unrelated to NO.