Radial artery has higher receptor-mediated contractility but similar endothelial function compared with mammary artery

Background. The radial artery (RA) has been used as an alternative arterial graft for coronary artery bypass grafting, but this artery has been suggested to be spastic. Endothelin-1 (ET) and angiotensin II (AII) have been measured with increased plasma concentrations during cardiopulmonary bypass. However, whether RA is reactive to these two important receptor-mediated vasoconstrictors is unknown. Also unknown is the endothelial function of this arterial conduit. This study was designed to compare RA and the internal mammary artery regarding the contractile characteristics to ET-1 and AII and endothelial function. Methods. Ring segments of the RA and internal mammary artery taken from patients undergoing coronary artery bypass grafting were studied in organ chambers at a physiologic pressure. The contractility was determined from the contraction induced by ET-1 and AII as contraction force and the force normalized by circumference (g/mm). The endothelium-dependent relaxation was induced by the calcium ionophore A23187, a nonreceptor agonist, and substance P, a receptor agonist for endothelium-derived relaxing factors. Nitroglycerin was used to study the endothelium-independent relaxation. Results. Both ET-1 and AII induced a higher contraction force (9.0 ± 0.9 g, n = 12, versus 4.5 ± 0.4 g, n = 38, p < 0.0001 for ET and 6.5 ± 1.9 g, n = 7, versus 1.7 ± 0.3 g, n = 8, p = 0.015 for AII) and normalized force (0.95 ± 0.1 g/mm versus 0.66 ± 0.05 g/mm, p = 0.007 for ET-1 and 0.8 ± 0.2 g/mm versus 0.2 ± 0.05 g/mm, p < 0.01 for AII) in RA than in the internal mammary artery. There were no significant differences detected between these arteries with regard to either endothelium-dependent (to substance P and A23187) or endothelium-independent (to nitroglycerin) relaxation (p > 0.05). Conclusions. We conclude that the human RA has a higher receptor-mediated contractility (to ET-1 and AII) but similar endothelial function compared to the internal mammary artery. The study reveals the nature of the more spastic characteristics of the RA, supports the necessity of a more active pharmacologic intervention to relieve spasm in the RA, and suggests that the similar endothelium-derived relaxing factor-mediated endothelial function of the RA compared with the internal mammary artery may be the basis for a satisfactory longterm patency.