Superoxide Anion Generation, Superoxide Dismutase Activity, and Nitric Oxide Release in Human Internal Mammary Artery and Saphenous Vein Segments

Abstract

Background: Internal mammary artery (IMA) as conduit for a coronary artery bypass graft (CABG) stays patent longer and more often than saphenous vein (SV). However, the pre cise differences in the biology of IMA and SV are unclear. Methods and Results: To examine inherent difference in superoxide anion, superoxide dis mutase (SOD) and nitric oxide (NO) formation in IMA and SV as a basis for differences in patency rates, we measured these parameters in vascular segments of patients undergoing CABG. Superoxide anion generation was measured by lucigenin chemiluminescence and reduction of cytochrome c, SOD by inhibition of pyrogallol auto-oxidation, and NO as nitrite/nitrate fluorometrically using 2-3-diaminonaphthalene as a probe. Generation of superoxide anion, SOD activity, and NO formation were all greater in the IMA than in the SV segments (IMA:SV = 2.6:1, 2.9:1, 1, and 3.0:1, respectively, all P < .01). There was a pos itive correlation between superoxide anion generation and SOD activity ( r = 0.65, P < .05; r = 0.70, P < .05 in IMA and SV, respectively) and NO release ( r = 0.68, P < .05; r = 0.75, P < .03 in IMA and SV, respectively). Western blot analysis showed no differences in SOD and NO synthase protein expression in IMA and SV segment homogenates. To examine whether greater superoxide anion generation, SOD activity, and NO formation are unique to IMA, we studied pulmonary artery (PA) and pulmonary vein (PV) segments taken from patients undergoing lung resection. Superoxide anion generation, SOD activity, and NO formation were also found to be greater in PA than in PV segments. Conclusions: Inherently greater superoxide anion generation and subsequently increased formation of SOD and NO release in IMA (vs SV) may be a factor in the greater patency of the former as CABG conduit. Because both IMA and PA are exposed to pulsatile stretch and carry blood at higher pressure than the SV and PV, it is likely that these 2 factors account for the observed differences.