Abstract 1439: Nitrite Functions As a Vascular Relaxing Factor Forming NO and Activating Guanylate Cyclase (sGC): Role of sGC in Nitrite-mediated NO Formation
Nitric oxide (NO) has been shown to be the endothelium-derived relaxing factor (EDRF), and its impairment contributes to cardiovascular disease. NO has been shown to exert its vasodilatory action through the activation of sGC. Recently, it has been recognized that nitrite can be an important source of NO, however, questions remain regarding the activity and mechanisms of bioactivation of nitrite in vessels. We demonstrate that nitrite (10 μM-1 mM) causes vasorelaxation of aortic rings, and NO is shown to be the intermediate factor responsible for this activity. Using electrochemical and electron paramagnetic resonance (EPR) techniques, we directly observe NO generation from isolated aortic vessels following nitrite treatment. A characteristic NO triplet EPR signal was seen in vessels with nitrite but no signal from nitrite alone (D vs A). Reduction of nitrite to NO was blocked by heating the vessel, suggesting that an enzymatic process is involved (B). Organ chamber experiments showed relaxation of the aorta induced by the addition of nitrite was blocked by the sGC inhibitors ODQ (10 μM) or NS2028 (1 μM). In addition, electrochemical measurements of NO formation showed that sGC inhibitors not only inhibit relaxation, but also inhibit NO formation from the aorta following nitrite administration. Similar results were observed with EPR spin trapping where isotope tracer studies of N15-nitrite definitively showed that nitrite is converted to NO with the appearance of a characteristic doublet signal (C). Since this NO formation was totally inhibited by sGC inhibitors, this indicates that vascular conversion of nitrite to NO is catalyzed by sGC or closed related heme enzymes.