Enhanced Nitric Oxide–Mediated Vascular Relaxation in Radial Artery Compared With Internal Mammary Artery or Saphenous Vein

Abstract

Background —The superior long-term patency of internal mammary artery coronary bypass grafts compared with venous grafts has been attributed in part to increased endothelium-derived nitric oxide (·NO) production. Interest in the radial artery as an alternative bypass conduit has recently been revived; however, its biological characteristics remain incompletely defined. The purpose of this study was to compare the ·NO-mediated vasomotor properties of the radial artery to those of the internal mammary artery and saphenous vein. Methods and Results —Matched segments of radial artery, internal mammary artery, and saphenous vein (n=24 patients) were examined by use of organ-chamber methodology. Endothelium-dependent and -independent vasomotor responses were assessed by dose-response curves to acetylcholine, N G -nitro- l -arginine methyl ester (L-NAME), 8-bromo-cyclic 3′,5′-guanosine monophosphate (8-bromo-cGMP), and nitroglycerin. Maximum ·NO-mediated radial artery relaxation in response to acetylcholine (86±10%) was significantly greater than internal mammary artery (56±9%) or saphenous vein (11±5%, both P <0.0001). Similarly, acetylcholine-stimulated cGMP accumulation in radial artery (9.1±1.7 pmol/mg protein) was also greater than internal mammary artery (6.2±0.3 pmol/mg protein) or saphenous vein (1.4±0.2 pmol/mg protein, both P <0.05). Estimated basal endothelial ·NO production, assayed as the percent maximum contraction in response to L-NAME, was greater in radial artery (39±5%) than internal mammary artery (23±6%) or saphenous vein (5±2%, both P <0.05). Maximum relaxation of all vessels to nitroglycerin was similar, although the sensitivity of radial artery to nitroglycerin was greater (EC 50 =33±7 nmol/L) than the internal mammary artery (203±32 nmol/L) or saphenous vein (97±12 nmol/L, both P <0.05). Vascular cGMP in response to 0.1 μmol/L nitroglycerin was significantly higher in the radial artery (8.3±1.4 pmol/mg protein) compared with the internal mammary artery (3.5±1.3 pmol/mg protein) or saphenous vein (1.4±0.3 pmol/mg protein, both P <0.0001). Relaxation to 8-bromo-cGMP was identical for all 3 conduits. Conclusions —These data indicate that ·NO-dependent relaxation of radial artery is greater than that of internal mammary artery or saphenous vein. This difference is related to endothelial production of ·NO and/or vessel sensitivity to ·NO. Such favorable physiological characteristics of radial artery could conceivably contribute to improved long-term patency of this conduit compared with saphenous vein.