Enhanced nitric oxide-mediated vascular relaxation in radial artery compared with internal mammary artery or saphenous vein.

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 micromol/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.