Abstract

Effect of preconditioning with ischemia, adenosine and SIN-1 of reperfusion-induced arrhythmias and purine release in isolated rat hearts

BACKGROUND: Adenosine is an important mediator of ischemic preconditioning (IPC) -induced cardioprotection in most species, excluding rat.
OBJECTIVE: To test the hypothesis that changes in adenosine metabolism induced by IPC, and/or by adenosine administered to mimic IPC, substantially differ between rat and other species. In addition, a hypothesis was tested that nitric oxide mediates the protective effect of IPC in rat heart.
METHODS: Reperfusion arrhythmias and effluent adenosine, inosine, hypoxanthine, xanthine and uric acid were examined in Langendorff perfused rat hearts subjected to 10 mins ischemia and 10 mins reperfusion. The hearts either were not pretreated before the 10 min ischemia (control group) or were preconditioned with 5 mins ischemia/5 mins reperfusion (IPC 5 min group), 5 mins ischemia/15 mins reperfusion (IPC 15 min group), 5 mins infusion of 10 mM adenosine followed by 5 mins washout (Ado[PC] group), and 5 mins infusion of 10 mM of the nitric oxide donor 3-morpholino-sydnonimine-hydrochloride (SIN-1), followed by 5 mins washout (SIN[PC] group).
RESULTS: Reperfusion arrhythmias were attenuated in the hearts subjected to IPC, an effect more pronounced in the IPC 5 min than in IPC 15 min group. Reperfusion arrhythmias were not affected in the Ado(PC) group and were significantly attenuated in the SIN(PC) group. Adenosine concentration was 0.28 mM, and micromolar concentrations of other purines were found in the effluent immediately upon reperfusion following preconditioning ischemia. The purines declined during the subsequent minutes of reperfusion. Similar profiles of purines were observed in the Ado(PC) group upon adenosine washout, although the maximum concentrations of purines were generally smaller in the Ado(PC) group, suggesting smaller interstitial concentrations of adenosine in this group. However, 10 mM adenosine attenuated by 63%, 56% and 53% the elevation of left ventricular developed pressure, +dp/dt and -dp/dt induced by 2.5 nM isoproterenol, confirming the efficacy of the adenosine infusion to stimulate adenosine receptors. During the reperfusion period following 10 mins ischemia, neither coronary flow nor release of purine metabolites differed between the control and IPC groups, while in the Ado(PC) group the release of inosine, hypoxanthine, xanthine and uric acid was significantly elevated compared with controls. Purine release was the same in the SIN(PC) group and in controls.
CONCLUSIONS: In rat hearts, IPC-induced protection against reperfusion arrhythmias is not mediated by adenosine, an effect not likely to be explained by peculiarities in adenosine metabolism in this preparation. Nitric oxide is able to mimic the effect of IPC on reperfusion arrhythmias in rat heart, supporting the view that nitric oxide may be one of the endogenous substances triggering IPC.