Objectives: To determine whether secondhand smoke (SHS) induces pulmonary artery endothelial dysfunction, and whether dietary L-arginine supplementation is preventive.
Background: SHS causes coronary and peripheral arterial endothelial dysfunction.
Methods: The effects of L-arginine supplementation (2.25% solution) and SHS (10 weeks) on pulmonary vascular reactivity were examined in 32 rabbits fed a normal diet. Endothelium-dependent relaxation of precontracted pulmonary artery segments was studied using acetylcholine and calcium ionophore. Endothelium-independent relaxation was studied using nitroglycerin. Endothelial and serum L-arginine levels were measured by chromatography. In eight SHS-exposed and in eight control rats, pulmonary artery nitric oxide synthase (NOS) activity and arginase activity were studied using the titrated arginine to citrulline conversion assay.
Results: SHS reduced maximal acetylcholine-induced (p = 0.04) and calcium ionophore-induced (p = 0.02) relaxation. L-Arginine increased maximal acetylcholine-induced (p = 0.047) vasodilation. SHS and L-arginine did not influence nitroglycerin-induced relaxation. SHS reduced endothelial L-arginine (p = 0.04) but not serum L-arginine. L-Arginine supplementation increased endothelial (p = 0.007) and serum L-arginine (p < 0.0005). Endothelium-dependent relaxation induced by acetylcholine and calcium ionophore varied directly with endothelial (r = 0.67, r = 0.67) and serum L-arginine (r = 0.43, r = 0.45), respectively. SHS reduced constitutive NOS activity (p = 0.03).
Conclusions: SHS reduces pulmonary artery endothelium-dependent relaxation by decreasing NOS activity and possibly by decreasing endothelial arginine content. L-Arginine supplementation increases serum and endothelial L-arginine stores and prevents SHS-induced endothelial dysfunction. L-Arginine may offset the deleterious effect of SHS on pulmonary arteries by substrate loading of the nitric oxide pathway.