Objective: Endothelial function is one of the important determinants of patency rate of a graft material used in coronary revascularisation. The aim of this study was to compare the endothelial reactivity of human gastroepiploic artery versus saphenous vein in response to various vasoactive substances. Methods: Gastroepiploic artery and saphenous vein rings were mounted in an organ bath containing Krebs-Ringer bicarbonate solution aerated with 95% O-2 and 5% CO2 at 37 degrees C. Endothelium dependent responses of acetylcholine, histamine, and bradykinin were examined on the precontracted rings of the vessels. The sensitivity of these two graft materials to the potent vasoconstrictor agent endothelin-1 was also compared. Results: Acetylcholine, histamine, and bradykinin caused dose dependent relaxations in saphenous vein and gastroepiploic artery rings. These agonists were more effective in producing endothelium dependent relaxations in the artery than in the vein. Endothelium removal and pretreatment with nitroarginine abolished the relaxations completely in saphenous vein but not in gastroepiploic artery, depending on the relaxing agent used. On the other hand, both graft materials showed nearly equal sensitivity to endothelin-1 (EC(50) values; 3.5 X 10(-9) M in the vein versus 6.4 X 10(-9) M in the artery, p=NS) which was not affected by endothelium removal. Conclusions: Gastroepiploic artery exhibited more pronounced relaxation and a different response profile to endogenous vasoactive substances than saphenous vein. The demonstration of higher capacity of the artery to release vasoactive substances in response to various endogeneous agents shows that gastroepiploic artery may have a better long term patency rate than saphenous vein.