| BackgroundBoth limb remote ischemic postconditioning and morphine can protect against the myocardial ischemia/reperfusion injury (IRI). This experiment was designed to assess whether combined morphine and limb remote ischemic postconditioning could provide an enhanced protection against myocardial IRI in an in vivo rat model.Part 1 Experimental study on cardioprotection of combining morohine and limb remote ischemic postconditioning against ischemia reperfusion injury in rat heart in vivoMethods:Sixty male Sprague-Dawley rats were randomly allocated into six groups: sham, ischemia reperfusion (IR), ischemic preconditioning (IPC), remote ischemic postconditioning (RIP), morphine (M), and combined morphine and remote ischemic postconditioning (M+RIP) groups. Ventricular arrhythmias during ischemia and early reperfusion were scored, and serum CK-MB and cTnI levels were assayed. The infarct size was determined by Evans blue and triphenyltetrazolium chloride staining.Results:The infarct size, serum cTnI level, incidence and score of arrhythmias during initial reperfusion were significantly reduced in the M+RIP group compared to the IR group, and did not significantly differ between IPC and M+RIP groups.Part 2 Experimental study on anti-apoptotic effects of combining morohine and limb remote ischemic postconditioning against ischemia reperfusion injury in rat heart in vivoMethods:Sixty male Sprague-Dawley rats were randomly allocated into four groups:ischemia reperfusion (IR), remote ischemic postconditioning (RIP), morphine (M), and combined morphine and remote ischemic postconditioning (M+RIP) groups. The apoptosis in the myocardial ischemic core, ischemic border and non-ischemic areas were assessed through real time PCR for Bax and Bcl-2 and Tunel assay. Optical microscope and electron microscope were used to determine the cardiomyocyte morphology.Results:Tunel positive cells were significantly decreased and Bcl-2/Bax ratio was significantly increased in the M+RIP group compared to the IR group. Myocardial cells had a comparative normal shape, and were regularly arranged, and mitochondria cristae were lucid in the M+RIP group.Part 3 Roles of the PI3K/Akt and JAK/STAT-3 signal pathways in the cardioprotection of combined morohine and limb remote ischemic postconditioningMethods:Eighty male Sprague-Dawley rats were randomly allocated into four groups:ischemia reperfusion (IR), remote ischemic postconditioning (RIP), morphine (M), and combined morphine and remote ischemic postconditioning (M+RIP) groups. The study was divided into two parts:the first part was that the myocardial tissue in the myocardial ischemic core, and non-ischemic areas were assessed through Western Blotting technique for phosphorylated Akt and STAT-3 and real time PCR for Akt and STAT-3; the second part was that PI3K inhibitor (LY294002) and JAK2 inhibitor (AG490) were given before conditioning to assess the role of PI3K/Akt and JAK/STAT-3 pathway in the cardioprotection.Results:p-STAT-3/STAT-3 and p-Akt/Akt ratio were significantly increased, and the transcription of STAT-3 and Akt was also significantly increased in the M+RIP group compared to the IR group. The PI3K inhibitor (LY294002) totally abolished the infarct sparing effect in M+RIP group, while the JAK2 inhibitor (AG490) partly abolished the infarct sparing effect in M+RIP group.Conclusions:Based on the results of all experiments, the following conclusions can be drawn:1. This experiment demonstrates that combined morphine and limb remote ischemic postconditioning provides a synergistic protection against myocardial IRI which is comparable to ischemic preconditioning.2. Combined morphine and limb remote ischemic postconditioning can provide a stronger cardioprotection by anti-apoptosis effects through Bcl-2 linked apoptotic signaling pathway.3. Combined morphine and limb remote ischemic postconditioning can significantly activate the PI3K/Akt and JAK/STAT-3 signal transduction pathway, which may contribute to its robust cardioprotection. |
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