Evidence for the involvement of peroxynitrite in ischaemic preconditioningin rat isolated hearts

1 The aim of this study was to investigate the involvement of peroxynitrite , reactive metabolite originating from nitric oxide and superoxide, in prec onditioning of the ischaemic myocardium in rat isolated hearts. 2 Isolated hearts perfused with Krebs-Henseleit solution were preconditione d either by 3 min of coronary artery occlusion (CAO) or by peroxynitrite ad ministration at three different concentrations (0.1, 1, 10 mu M) for 3 min, followed by 10 min reperfusion and 30 min of CAO. Peroxynitrite, at 1 mu M concentration, decreased the incidence of VT from 100% (n=14) to 62% (n=13 ) and abolished the occurrence of VF (50% in the control group). 3 N-2-mercaptopropionylglycine (MPG, 1 mu M-10 mM) produced a concentration -dependent inhibition of peroxynitrite signals in luminol chemiluminescence and 67+/-1% inhibition was observed at 100 mu M (n = 7). MPG (at 300 mu M, n = 7) added to the perfusate 10 min prior to ischaemic preconditioning or peroxynitrite infusion and maintained until CAO, significantly reversed th e beneficial effects of the ischaemic and peroxynitrite-treated groups. MPG administration in the peroxynitrite-treated group increased the incidence of VT from 62% (n=13) to 100% (n=10) and total VF from 0% (n=0) to 67% (n=1 0). Similarly, MPG elevated the incidence of VT from 50% (n=10) to 100% (n= 8) in the ischaemic preconditioned group. On its own, MPG did not affect th e severity of cardiac arrhythmias. 4 These results suggest that endogenously produced peroxynitrite plays a si gnificant role in the antiarrhythmic effect of ischaemic preconditioning in the rat isolated hearts.