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

The aim of this study was to investigate the involvement of peroxynitrite, reactive metabolite originating from nitric oxide and superoxide, in preconditioning of the ischaemic myocardium in rat isolated hearts. Isolated hearts perfused with Krebs‐Henseleit solution were preconditioned either by 3 min of coronary artery occlusion (CAO) or by peroxynitrite administration at three different concentrations (0.1, 1, 10 μ M ) for 3 min, followed by 10 min reperfusion and 30 min of CAO. Peroxynitrite, at 1 μ 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). N‐2‐mercaptopropionylglycine (MPG, 1 μ M –10 m M ) produced a concentration‐dependent inhibition of peroxynitrite signals in luminol chemiluminescence and 67±1% inhibition was observed at 100 μ M ( n =7). MPG (at 300 μ M , n =7) added to the perfusate 10 min prior to ischaemic preconditioning or peroxynitrite infusion and maintained until CAO, significantly reversed the 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 =10). 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 the severity of cardiac arrhythmias. These results suggest that endogenously produced peroxynitrite plays a significant role in the antiarrhythmic effect of ischaemic preconditioning in the rat isolated hearts.British Journal of Pharmacology (2000) 130 , 125–131; doi: 10.1038/sj.bjp.0703280