Comparison of endothelium-dependent responses of canine internal thoracic and coronary arteries.

The endothelium-dependency of vasodilator responses was compared in helical strips of canine internal thoracic (ITA) and coronary arteries partially contracted with serotonin. The addition of acetylcholine produced a concentration-related relaxation in ITA and coronary arterial strips with an intact endothelium. The relaxations were not influenced by indomethacin, but were markedly inhibited or abolished by methylene blue, NG-nitro-L-arginine (L-NA), a nitric oxide (NO) synthase inhibitor, and endothelial denudation. The responses to low concentrations of acetylcholine were significantly greater in ITA than in coronary arteries, whereas relaxations induced by substance P, Ca2+ ionophore (A23187) or NO in ITA were significantly less. The substance P-induced relaxation in ITA and coronary arteries was endothelium-dependent, and it was almost abolished by L-NA. Relaxations induced by ATP in ITA were abolished by endothelium denudation and treatment with L-NA. In the coronary arteries, relaxing responses were inhibited only partially by removal of endothelium and L-NA. Acetylcholine, ATP and substance P relax canine ITA possibly by a mediation of endothelium-derived NO, but not prostaglandin I2. Coronary arterial relaxations induced by ATP appear to be mediated by an indirect action via NO released from the endothelium, in addition to a direct action on the smooth muscle.