Abstract-Proinflammatory stimuli produce expression of inducible NO-synthase (iNOS) within blood vessels and are associated with impaired endothelium-dependent relaxation. Gene transfer of iNOS was used to test the hypothesis that expression of iNOS in blood vessels produces impairment of NO-dependent relaxation as well as contraction. An adenoviral vector containing cDNA for murine iNOS, AdCMViNOS, and a control virus, AdCMVBglII, were used for gene transfer to rabbit carotid arteries in vitro and in vivo. After gene transfer of iNOS in vitro, contractile responses to KCl, phenylephrine, and U46619 were impaired. Relaxation in response to acetylcholine, ADP, A23187, and nitroprusside was also impaired. For example, maximum relaxation of vessels to acetylcholine (10 mol/L) was 78Ϯ4% (meanϮSE) after AdBglII (10 10.5 plaque-forming units) and 34Ϯ5% after AdiNOS (10 10.5 plaque-forming units, PϽ0.05). NO-independent relaxation in response to 8-bromo-cGMP and papaverine was not impaired after AdiNOS. Contraction and relaxation were improved in carotid arteries expressing iNOS by aminoguanidine and L-N-iminoethyl lysine, inhibitors of iNOS. After intraluminal gene transfer of iNOS in vivo, contraction of vessels in vitro was normal, but responses to acetylcholine were impaired. In summary, the major finding is that NO-dependent relaxation is impaired in arteries after gene transfer of iNOS in vitro and in vivo. Key Words: superoxide Ⅲ NO-dependent relaxation Ⅲ adenovirus Ⅲ acetylcholine Ⅲ nitroprusside A lthough normal blood vessels do not express inducible NO-synthase (iNOS), vascular expression of iNOS occurs in pathological settings, including cerebrovascular disease and stroke. 1,2 In general, proinflammatory stimuli produce the expression of iNOS within the vessel wall. [3][4][5][6][7][8] Expression of iNOS during systemic inflammation contributes to impaired contraction, 3,4,9,10 but effects of iNOS on vasorelaxation have not been clearly established. Several studies suggest that vasorelaxation is impaired after inflammatory stimuli, such as lipopolysaccharide (LPS), 11-14 but others report normal vasorelaxation after LPS. 15,16 The goal of these studies was to examine effects of iNOS on contraction and relaxation of blood vessels by using gene transfer of iNOS.
See page 1259Endothelium-dependent vasorelaxation mediated by endothelial NO synthase (eNOS) is impaired in response to several inflammatory stimuli that induce iNOS in blood vessels. 12,[17][18][19] Pharmacological inhibitors of iNOS improve endothelium-dependent relaxation after LPS. 12,20,21 The findings suggest that expression of iNOS is associated with decreased function of eNOS. However, pharmacological inhibitors of iNOS are not entirely selective for iNOS, and inhibition of neuronal NO synthase also improves endothelium-dependent relaxation during inflammation. 20 Therefore, it is not known whether iNOS, per se, affects relaxation of blood vessels.The goal of the present study was to use gene transfer of iNOS, in vitro and in vivo, to directly e...