Effects of l-arginine on atherogenesis and endothelial dysfunction due to secondhand smoke
Secondhand smoke (SHS) and hypercholesterolemia increase cardiovascular risk. We hypothesized that L-arginine, the precursor of nitric oxide (NO), might protect against atherogenesis and endothelial dysfunction caused by SHS. The effects of L-arginine supplementation (2.25% solution ad libitum) and SHS (smoking chambers for 10 weeks) were examined in 32 hypercholesterolemic rabbits. Eight normal rabbits served as controls. Acetylcholine- and nitroglycerin-induced vasorelaxation was assessed in aortic rings precontracted with norepinephrine. Hypercholesterolemia increased intimal lesion area (P=0.012), reduced endothelium-dependent relaxation (P=0.009), and reduced basal (P=0.005) and stimulated (P<0.0005) production of NOs. SHS increased intimal lesion area (P=0. 01) norepinephrine-induced contraction (P=0.001) and reduced endothelium-dependent relaxation (P=0.02). SHS-induced increase in norepinephrine contraction was abolished by the inhibition of NO synthase and removal of endothelium. L-Arginine improved endothelium-dependent relaxation (P=0.001) and attenuated SHS-induced endothelial dysfunction (P=0.007) and atherogenesis (P=0. 001). Basal production of nitrogen oxides correlated inversely with intimal lesion area (r=-0.66; P<0.0005) and stimulated production of NOs correlated with endothelium-dependent relaxation (r=-0.66; P<0. 001). SHS causes endothelial dysfunction and increased adrenergic responsiveness and atherogenesis in hypercholesterolemic rabbits. Chronic dietary supplementation with the NO precursor L-arginine mitigates these effects. The adverse vascular consequences of SHS appear to be mediated via deleterious effects on endothelial function.