ABSTRACT
Effect of acetylcholine(ACh) and McN-A-343 on porcine coronary artery and rabbit thoracic aorta were investigated in isolated preparations with or without intact endothelium. In the porcine coronary artery, ACh produced concentration dependent contraction which was greater in rings without the endothelium than in intact endothelial rings, but McN-A-343 did not alter the basel tension in both tissues. ACh relaxed contraction induced by 5-hydroxytryptamine(5-HT) in only intact endothelial rings, while NcN-A-343 inhibited the 5-HT induced tension in both preparations dose dependently. Carbachol elicited a prominent contraction in both tissues. The carbacol-induced tension was markedly inhibited by McN-A-343 in either rings with or without endothelium, while ACh contracted further the tension. ACh and McN-A-343 did not after the KCi induced tension, but clearly potentiated the contraction induced by Bay K 8644 in intact endothelial rings. In rabbit thoracic aorta, ACh elicited contraction in a concentration-dependent fashion which was potentiated by removal of endothelium, but McN-A-343 did not affect the basal tension of both rings. ACh inhibited the 5-HT-induced contraction in only intact endothelial ring, but McN-A-343 did not change the contraction of both rings. Conclusively, ACh produces endothelium-dependent relaxation in both arteries, while McN-A-343 elevated endothelium-independent inhibition to 5-HT or carbachol-induced tension.