CONSTITUTIVE NITRIC-OXIDE SYNTHASE IS EXPRESSED AND NITRIC OXIDE-MEDIATED RELAXATION IS PRESERVED IN RETRIEVED HUMAN AORTOCORONARY VEIN GRAFTS

Although little is known about the endothelial cell function of human saphenous vein coronary artery bypass grafts, there is evidence to sug gest that receptor-activated, endothelial-dependent relaxation mediate d by nitric oxide is impaired. This study examines the expression and function of endothelial cell constitutive nitric oxide synthase (cNOS) of aortocoronary vein bypass grafts and human saphenous veins obtaine d from 10 patients undergoing repeat coronary artery bypass grafting f or recurrent ischemic symptoms. Following precontraction with norepine phrine (10(-5) M), responses to acetylcholine (receptor-mediated, endo thelium-dependent), calcium ionophore (A23187; receptor-independent, e ndothelium-dependent), and sodium nitroprusside (endothelium-independe nt) were assessed. Following total RNA extraction using phenol/guanidi nium isothiocyanate from specimens of human saphenous vein and vein gr aft, a quantitative RNase Protection Assay (RPA) was performed using a cRNA riboprobe corresponding to a fragment of the human endothelial c ell cNOS gene. Histologically, the vein grafts showed both intimal hyp erplasia development and focal atherosclerosis formation compared to t he saphenous veins. Scanning electron microscopy of the saphenous vein s and the vein grafts showed an intact endothelium. Precontracted vein grafts did not relax in response to acetylcholine; in contrast, the s aphenous vein relaxed in a dose-dependent manner to reach a maximal re laxation of 19 +/- 4% precontracted tension. Saphenous veins and vein grafts relaxed in response to A23187 with maximal relaxation of 92 +/- 5 and 73 +/- 13%, respectively. Both vessels relaxed in a dose depend ent manner to sodium nitroprusside. RPA normalized to beta-actin showe d similar levels of expression of endothelial cell cNOS equivalent to 1 pg of sense RNA in both the saphenous vein and vein graft, These dat a demonstrate that the endothelium of coronary artery vein grafts show s both expression and function of endothelial cell cNOS. However, the impaired NO-mediated relaxation of aortocoronary vein grafts in respon se to acetylcholine appears to be due to altered receptor activation o f the endothelial cNOS system. (C) 1995 Academic Press, Inc.