Cardioprotective activity of the adipocytokine apelin is attributed to upregulation of endothelial nitric oxide synthase (NOS). This study was designed to examine effects of a synthesized 12 C-terminal residue of apelin (A-12) and NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NOS inhibitor, in ex vivo and in vivo models of ischemia/reperfusion injury.Methods
Isolated working rat hearts were subjected to 35-min global ischemia followed by 30-min reperfusion. 140 μM A-12 and 100 μM L-NAME were administered separately or in combination before global ischemia. Metabolic state of reperfused hearts and lactate dehydrogenase (LDH) leakage in perfusate were assessed by enzymatic methods. Anaesthetized open-chest rats were subjected to 40-min regional ischemia and 60-min coronary reperfusion. L-NAME (37 μmol/kg 10 min prior to reperfusion) and A-12 (0.35 μmol/kg at the onset of reperfusion) were injected intravenously; control rats received saline. Myocardial injury was evaluated by MB-creatine kinase (MB-CK) and LDH activities in plasma. Infarct size was determined by the Evans Blue/2,3,5-triphenyl tetrazolium chloride staining method.Results
Preischemic infusion of A-12 increased recovery of cardiac function during reperfusion compared with control and resulted in enhanced restoration of myocardial ATP, adenine nucleotide pool, phosphocreatine and reduction of myocardial lactate and lactate/pyruvate ratio. Coadministration of A-12 and L-NAME aggravated recovery of coronary flow and cardiac function compared with these indices after A-12 treatment. Cardiac dysfunction was associated with increase in LDH release in myocardial effluent, reduction of glucose oxidation and abolishment of augmented restoration of high energy phosphates. A-12 administration after regional ischemia in anesthetized rats led to a transient reduction of mean arterial blood pressure (MABP), significant limitation of infarct size expressed as a percent of area at risk (MI/AR, %) and decreased LDH and MB-CK activities in plasma at the end of reperfusion compared with control. Subsequent administration of L-NAME and A-12 resulted in less reduction of MABP and substantially increased MI/AR ratio and MB-CK and LDH activities in plasma compared to the values in the A-12 group.Conclusions
The results demonstrate the principal role of NO as a mediator of overall cardioprotection afforded by apelin.