Objectives: Our objective was to determine the effect of a nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NNA) on free radical generation and myocardial contractility after ischemia-reperfusion.
Background: Cardiotoxic free radicals are generated by ischemia-reperfusion sequences. Nitric oxide reacts with superoxide radical to form peroxynitrite, which generates additional free radicals. Our hypothesis was that by inhibiting NO production, free radical formation will be diminished, which should be cardioprotective.
Methods: We studied 32 dogs. Coronary occlusion-reperfusion (20 min each) sequences were created by intracoronary balloon angioplasty inflation-deflation. Using electron paramagnetic resonance, we monitored the coronary sinus concentration of ascorbate free radical (Asc*-), a measure of total oxidative flux. The L-NNA (4.8 mg/kg total) was infused intravenously during occlusion-reperfusion; control dogs received saline. Immunohistochemical staining demonstrated the peroxynitration product nitrotyrosine.
Results: In the control dogs Asc*- rose from 3.2 +/- SD 0.5 nmol/l to 4.8 +/- 1.1 nmol/l with reperfusion, a 50% rise. With L-NNA the Asc*- rose from 3.2 +/- 0.9 nmol/l to 4.0 +/- 1.2 nmol/l, a 25% rise (p < 0.01, L-NNA vs. control). Echocardiographic left ventricular fractional area shortening (FAS) in the control dogs declined from 38 +/- 19% (baseline) to 26 +/- 14% (ischemia), and to 22 +/- 11% with reperfusion (p < 0.01 vs. baseline). With L-NNA, FAS declined from 36 +/- 13% (baseline) to 27 +/- 12% (ischemia) but then rose to 33 +/- 14 with reperfusion (p = NS vs. baseline). Nitrotyrosine was present in the myocardium subjected to ischemia-reperfusion, but almost absent in dogs receiving L-NNA. Myocardial perfusion was not altered by L-NNA.
Conclusions: The NO synthase inhibitors decrease coronary sinus free radical concentration and ameliorate myocardial stunning after ischemia-reperfusion.