The role of nitric oxide, superoxide and peroxynitrite in the anti‐arrhythmic effects of preconditioning and peroxynitrite infusion in anaesthetized dogs

Abstract

Background and purpose: Both ischaemia preconditioning (PC) and the intracoronary infusion of peroxynitrite (PN) suppress ischaemia and reperfusion (I/R)-induced arrhythmias and the generation of nitrotyrosine (NT, a marker of PN). However, it is still unclear whether this latter effect is due to a reduction in nitric oxide (NO) or superoxide (O2 -) production. Experimental approach: Dogs anaesthetized with chloralose and urethane were infused, twice for 5 min, with either saline (control) or 100 nM PN, or subjected to similar periods of occlusion (PC), 5 min prior to a 25 min occlusion and reperfusion of the left anterior descending coronary artery. Severities of ischaemia and ventricular arrhythmias, as well as changes in the coronary sinus nitrate/nitrite (NOx) levels were assessed throughout the experiment. The production of myocardial NOx, O2 -and NT was determined following reperfusion. Key results: Both PC and PN markedly suppressed the I/R-induced ventricular arrhythmias, compared to the controls, and increased NOx levels during coronary artery occlusion. Reperfusion induced almost the same increases in NOx levels in all groups, but superoxide production and, consequently, the generation of NT were significantly less in PC-and PN-treated dogs than in controls. Conclusions and implications:Since both PC and the administration of PN enhanced NOx levels during I/R, the attenuation of endogenous PN formation in these dogs is primarily due to a reduction in the amount of O2 produced. Thus, the anti-arrhythmic effect of PC and PN can almost certainly be attributed to the preservation of NO availability during myocardial ischaemia.

The effect of acute simvastatin administration on the severity of arrhythmias resulting from ischaemia and reperfusion in the canine: Is there a role for nitric oxide?

“…This protection against arrhythmias was similar to that we have obtained previously in the same model with ischaemic preconditioning (Végh et al, 1992a), and with the administration of NO donors (Gyorgy et al, 2000;Gonczi et al, 2009;Kiss et al, 2010). Furthermore, the present study confirmed the role of eNOS activation in the antiarrhythmic effect of simvastatin, since both the phosphorylation of eNOS (determined by Western blot) and Fluorescence intensity (arbitrary units) Fig.…”

“…6). We have previous evidence that the preservation of NO bioavailability during coronary artery occlusion by preconditioning or by donating NO attenuates the reperfusion-induced marked increases of superoxide production (Kiss et al, 2010). Furthermore, the fact that L-NAME prevented the simvastatin activated enzyme to form NO (inhibits the L-arginine-NO pathway without affecting enzyme phosphorylation) and attenuated or even abolished most of the salutary effects of simvastatin, supports the hypothesis that the eNOS activated NO formation plays a crucial role in the protective effect of simvastatin against arrhythmias.…”

“…Schwartz et al, 1995) and of gap junction function (Gonczi et al, 2009), as well as the regulation of free radical formation by NO (e.g. Iwase et al, 2007;Kiss et al, 2010).…”

“…These were performed as described previously (Kiss et al, 2010). Plasma nitrate/nitrite (NO x ) concentrations were determined by means of the Griess reaction in blood samples taken from the coronary sinus at various time intervals as illustrated in Fig.…”

“…This was determined by dihydroethidium (DHE; SigmaAldrich) fluorescence staining as described previously (Kiss et al, 2010). Briefly, tissue blocks, excised from the ischaemic myocardial wall were embedded in optimal cutting temperature compounds.…”