title: Inducible nitric oxide synthase-derived superoxide contributes to hypereactivity in small mesenteric arteries from a rat model of chronic heart failure.
abstract: The aims of this study were to (a) determine whether inducible nitric oxide synthase (iNOS) is expressed in small mesenteric arteries from rats with chronic heart failure (CHF), (b) investigate the functional significance of this potential source of nitric oxide (NO) on vascular responsiveness and (c) investigate the role that superoxide plays in modulating vascular function in these arteries. CHF was induced in male Wistar rats by coronary artery ligation (CAL). In sham-operated rats the ligature was not tied but pulled under the artery. Six weeks after surgery CAL rats had left ventricular (LV) infarctions and elevated LV end-diastolic pressures. Immunoreactive iNOS was found in endothelial cells, vascular smooth muscle cells and in the adventitia of small mesenteric arteries from CAL rats but not those from sham-operated rats. Third order mesenteric arteries (300-350 microm) were mounted in a small vessel pressure myograph. Endothelium-intact arteries from CAL rats were more responsive to phenylephrine (PE) than arteries from sham-operated rats (pD(2) value, CAL, 6.2+/-0.1; sham-operated, 5.9+/-0.1, P<0.05). Both the selective iNOS inhibitor, N-(3-(Aminomethyl) benzyl) acetamidine dihydrochloride (1400W; 10(-6) M) and the superoxide dismutase mimetic, Mn [III] tetrakis [1-methyl-4-pyridyl] porphyrin, (MnTMPyP; 10(-4) M) reversed the hyperesponsiveness (pD(2) values, 1400W, 5.9+/-0.1; MnTMPyP, 5.81+/-0.1, P<0.05). The NOS substrate, L-arginine (10(-3) M), reduced responsiveness of endothelium-denuded small mesenteric arteries from CAL rats (P<0.01). None of these drugs altered responses to PE in arteries from sham-operated rats. In summary, this study demonstrates that iNOS is expressed in mesenteric arteries from rats with CHF. However, instead of generating large quantities of NO, iNOS appears to be generating superoxide, perhaps because of a deficiency in its substrate, L-arginine. Increased superoxide generation from iNOS contributes to the hyperesponsive nature of endothelium-intact small mesenteric arteries from rats with CHF.
authors.affiliation: Endothelial Cell Biology and Molecular Cardiology Section, Centre for Cardiovascular Science, Department of Biomedical Sciences, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, EH8 9LD.
authors.forename: A A
authors.initials: AA
authors.lastname: Miller
authors.forename: I L
authors.initials: IL
authors.lastname: Megson
authors.forename: G A
authors.initials: GA
authors.lastname: Gray
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D003327:Coronary Disease / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D004727:Endothelium / Q000502:physiology; D006333:Heart Failure / Q000503:physiopathology*; D007150:Immunohistochemistry; D008297:Male; D008638:Mesenteric Arteries / Q000503:physiopathology*; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013481:Superoxides / Q000378:metabolism*; D014664:Vasodilation
chemical_list: D013481:Superoxides; D009569:Nitric Oxide; D011189:Potassium Chloride; D001120:Arginine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat