Heme proteins mediate the conversion of nitrite to nitric oxide in the vascular wall.
Nitric oxide (NO) has been shown to be the endothelium-derived relaxing factor (EDRF), and its impairment contributes to a variety of cardiovascular disorders. Recently, it has been recognized that nitrite can be an important source of NO; however, questions remain regarding the activity and mechanisms of nitrite bioactivation in vessels and its physiological importance. Therefore, we investigated the effects of nitrite on in vivo hemodynamics in rats and in vitro vasorelaxation in isolated rat aorta under aerobic conditions. Studies were performed to determine the mechanisms by which nitrite is converted to NO. In anesthetized rats, nitrite dose dependently decreased both systolic and diastolic blood pressure with a threshold dose of 10 microM. Similarly, nitrite (10 microM-2 mM) caused vasorelaxation of aortic rings, and NO was shown to be the intermediate factor responsible for this activity. With the use of electrochemical as well as electron paramagnetic resonance (EPR) spectroscopy techniques NO generation was measured from isolated aortic vessels following nitrite treatment. Reduction of nitrite to NO was blocked by heating the vessel, suggesting that an enzymatic process is involved. Organ chamber experiments demonstrated that aortic relaxation induced by nitrite could be blocked by both hemoglobin and soluble guanylyl cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ). In addition, both electrochemical and EPR spin-trapping measurements showed that ODQ inhibits nitrite-mediated NO production. These findings thus suggest that nitrite can be a precursor of EDRF and that sGC or other heme proteins inhibited by ODQ catalyze the reduction of nitrite to NO.
Davis Heart and Lung Research Institute, The Ohio State Univ., 473 West 12Ave., Columbus, OH 43210, USA.
Wael F
WF
Alzawahra
M A Hassan
MA
Talukder
Xiaoping
X
Liu
Alexandre
A
Samouilov
Jay L
JL
Zweier
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D001794:Blood Pressure; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry / Q000379:methods; D004578:Electron Spin Resonance Spectroscopy; D045462:Endothelium-Dependent Relaxing Factors / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006339:Heart Rate; D006420:Hemeproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D007262:Infusions, Intravenous; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000008:administration & dosage / Q000378:metabolism*; D010069:Oxadiazoles / Q000494:pharmacology; D010108:Oxyhemoglobins / Q000378:metabolism; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D000071756:Soluble Guanylyl Cyclase; D014664:Vasodilation / Q000187:drug effects
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D045462:Endothelium-Dependent Relaxing Factors; D004791:Enzyme Inhibitors; D006420:Hemeproteins; D009573:Nitrites; D010069:Oxadiazoles; D010108:Oxyhemoglobins; D011810:Quinoxalines; D018160:Receptors, Cytoplasmic and Nuclear; D009569:Nitric Oxide; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase