Notes on the acetylcholine-induced relaxation of porcine coronary arteries.

Intact and rubbed coronary arteries responded to acetylcholine (ACh) with contractions in a cumulative dose-dependent manner. The rubbed artery contracted at a lower concentration of ACh (3 x 10(-8) M) than the threshold level of the agonist in the intact artery (10(-7) M). Only in the intact artery was the second cumulative dose-response to ACh (10(-6) M) decreased by 60% (p < 0.05). Pretreatment of the intact artery with methylene blue or NG-monomethyl-L-arginine (L-NMMA) increased the contractile response to ACh. The ACh-induced increase of the cGMP level in the intact artery was eliminated by removal of the endothelial cells and by pretreatment of the artery with either methylene blue or L-NMMA. These findings indicate that the endothelial cells in the coronary artery are responsible for the ACh-induced relaxation, presumably mediated by an endothelium-derived relaxing factor.