Is there a trigger role of peroxynitrite in the anti-arrhythmic effect of ischaemic preconditioning and peroxynitrite infusion?

This study has examined whether peroxynitrite (PN), generated during the preconditioning (PC) procedure or administered by brief intracoronary infusions, plays a trigger role in the anti-arrhythmic effects of preconditioning and peroxynitrite in anaesthetized dogs. To achieve this we infused the peroxynitrite scavenger uric acid (UA; 0.2 mg/kg/min, i.v.) over a 30 min period, just prior to a 25 min occlusion of the left anterior descending coronary artery, in preconditioned (UA+PC, n=8), peroxynitrite-treated (UA+PN, n=8) and in control (UAC; n=9) dogs. The effects were compared to those obtained from groups (PC, n=10; PN, n=10; C1, n=14) without uric acid administration. Severities of ischaemia (ST-segment elevation, inhomogeneity of electrical activation) and ventricular arrhythmias (VPBs, VT, VF), plasma nitrate/nitrite levels, as well as myocardial superoxide and nitrotyrosine productions were determined. Both preconditioning and the infusion of peroxynitrite increased nitrotyrosine formation which was abolished by the simultaneous administration of urate. Despite this, the protective effects of preconditioning (i.e. reductions in arrhythmias, superoxide and nitrotyrosine productions, as well as the increase in nitric oxide availability), occurring during the prolonged period of occlusion and reperfusion were still present. In contrast, urate completely abolished the protection resulted from peroxynitrite administration. This effect is most probably due to the fact that urate has already scavenged peroxynitrite during the infusion. Interestingly, urate itself, given prior to ischaemia and reperfusion, was also protective. We conclude that peroxynitrite in nanomolar concentrations can induce an anti-arrhythmic effect but peroxynitrite, generated during the preconditioning stimulus, is not necessary for the preconditioning-induced anti-arrhythmic protection.