| Background: Myocardial ischemia reperfusion injury (MIRI) is one of the most important complications followed by the heart transplantation, intracoronary thrombolysis, percutaneous coronary intervention and the coronary artery bypass graft surgery after acute myocardial infarction. Therefore, it is extremely valuable to explore the clinically feasible and effective therapeutic strategies attenuating MIRI. A novel cardioprotective strategy, ischemic postconditioning (IPO), has been reported in recent years. IPO means that the brief episodes of reperfusion-ischemia reduces the injury caused by following long period of reperfusion. Hydrogen sulfide (H2S) is an endogenous gaseous mediator,produced by cystathionine-γ-lyase (CSE) in the cardiovascular system during the L-cysteine metabolism. The administration of exogenous H2S can effectively decrease myocardial ischemia injury. It is not yet clear whether the endogenous CSE/H2S pathway can be a mediator for the antagonist effect of ischemic postconditioning against myocardial ischemia-reperfusion injury. Objective: To explore whether the endogenous CSE/H2S pathway can mediate the antagonist effect of ischemic postconditioning against myocardial ischemia-reperfusion injury in rat.Methods: Sprague-Dawley (SD) rat was sacrificed and heart was mounted on a Langendorff apparatus and retrogradely perfused with K-H solution in order to establish the isolated whole heart ischemic reperfusion model. 40 SD rats were randomly divided into 5 groups. (1)Ischemic reperfusion group (group IR): the hearts were subjected to ischemia by stopping perfusion for 30min followed by reperfusion for 90min; (2)ischemic postconditioning group (group IPO): the operation on hearts was the same as group IPO, but before the long period of reperfusion the hearts were treated with postcondtioning, which were implemented by the repeated 10s of reperfusion and 10s of ischemia for 6 circles and followed by 88min of reperfusion; (3) PAG+IPO group (group PAG): the operation on hearts was the same as group IPO, but rats were injected with L-propargylglycine (PAG, the inhibitor of CSE) (20mg/kg) intraperitoneally before the operation; (4) PAG+IPO+NaHS group (group PPN): the operation on hearts was the same as group PAG, but during the reperfusion period the hearts were reperfused with K-H solution including exogenous H2S donor NaHS (40umol/L) for 90min; (5) PAG+NaHS group (group PIN): rats were injected with PAG(20mg/kg) before sacrifice, but during the reperfusion period the hearts were reperfused with K-H solution including exogenous H2S donor NaHS (40umol/L) for 90min. The heart rate (HR), coronary arterial flow (CF), left ventricular developed pressure (LVDP) were examined. The activity of lactate dehydrogenase (LDH) and creatine kinase (CK) in the coronary effluent fluid, and the activity of CSE and the content of H2S in the isolated rat hearts were measured with the method of colorimetry. The infarction size was measured with TTC staining.Results: There was no significant difference between groups in parameters at the basal level before ischemia. During and after reperfusion, the cardiac mechanic function was downtrend in all groups, which indicated that ischemia-reperfusion injury occurred. The results showed that there was no significant difference of CF level among all groups after reperfusion (P>0.05). After 30 minutes of reperfusion, the HR in group IPO and PIN and PPN showed a significant increase compared to group IR and PAG (P<0.05). Compared with group IR, the LVDP level in the group IPO were most notably increased by 173.45% at 60 minutes after reperfusion, with the cardiac functions improving significantly along with the reperfusion and LDH/CK activity decreasing, the infarct size decreasing by 60.87%, and the activity of CSE and the content of H2S in myocardium increased by 126.96% and 139.43%(all P<0.05). 90 minutes post reperfusion, the results showed that PAG administration caused the level of LVDP to decrease by 79.65% and the activity of CSE by 76.78% and the content of H2S by 77.85%, and the LDH/CK activity to increase (by 76.78%, 77.85%) and the infarct size by 170.71%, compared with group IPO (all P<0.05). Compared with group IR, the LVDP level in group PPN and PIN were showed a remarkable increase (by 140.12%, 93.93%) and the infarct size decrease (by 57.09%, 62.68%), and LDH activity were caused significantly to decrease (by 39.52%, 36.93%) and CK activity decreased (by 34.52%, 27.98%) (all P<0.05). There were no significant difference among the level of every parameter between group IPO and group PIN and group PN except the activity of LDH in group PIN increasing by 20.02% and 15.69% (P<0.05) compared with that in group IPO and group PPN 15 minutes after reperfusion.Conclusion:1. IPO can exert an antagonist role against MIRI in isolated rat heart;2. PAG(the inhibitor of CSE)can attenuate the antagonist influence induced by IPO against MIRI;3. IPO can cause an increase of the level of CSE/H2S in isolated rat heart ;4. Endogenous CSE/H2S pathway can be a mediator for the antagonist effect of IPO against MIRI.
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