Abstract—Linoleic acid, a polyunsaturated C18fatty acid, is one of the major fatty acids in the coronary arterial wall. Although diets rich in linoleic acid reduce blood pressure and prevent coronary artery disease in both humans and animals, very little is known about its mechanism of action. We believed that its beneficial effects might be mediated by changes in vascular tone. We investigated whether linoleic acid induces relaxation of porcine coronary artery rings and the mechanism involved in this process. Linoleic acid and two of its metabolites, 13-hydroxyoctadecadienoic acid (13-HODE) and 13-hydroperoxyoctadecadienoic acid (13-HPODE), induced dose-dependent relaxation of prostaglandin (PG) F2α–precontracted rings that was not affected by indomethacin (10−5mol/L), a cyclooxygenase inhibitor, or cinnamyl-3,4-dihydroxy-α-cyanocinnamate (CDC; 10−5mol/L), a lipoxygenase inhibitor. Removal of endothelial cells had no effect on vasorelaxation, suggesting a direct effect on the vascular smooth muscle cells (VSMC). When rings were contracted with KCl, linoleic acid failed to induce relaxation. Although tetrabutylammonium (5×10−3mol/L), a nonselective K+channel blocker, slightly inhibited the relaxation caused by linoleic acid, glibenclamide (10−6mol/L), an ATP-sensitive K+channel blocker, and charybdotoxin (7.5×10−8mol/L) or tetraethylammonium (5×10−3mol/L), two different Ca2+-activated K+channel blockers, had no effect. However, relaxation was completely blocked by ouabain (5×10−7mol/L), a Na+/K+-ATPase inhibitor, or by a K+-free solution. In addition, linoleic acid (10−6mol/L) caused sustained hyperpolarization of porcine coronary VSMC (from -49.5±2.0 to -60.7±4.2 mV), which was also abolished by ouabain. We concluded that linoleic acid induces relaxation and hyperpolarization of porcine coronary VSMC via a mechanism that involves activation of the Na+/K+-ATPase pump.