Objective To evaluate the effects of morphine preconditioning-postconditioning on ischemia-reperfusion (I/R) injury in isolated rat hearts. Methods Male SD rats weighing 180-200 g were killed after intraperitoneal injection of heparin 500 U/kg. The hearts were immediately removed and perfused in a Langendorff apparatus with K-H solution gassed with 95%O2-5%CO2 .HR and left ventricular systolic pressure (LVSP) were measured from a fluid-filled latex balloon in the left ventricle. Global myocardial ischemia was induced by interrupting perfusion for 45 min followed by 60 min reperfusion. Forty isolated rat hearts were randomly divided into 5 groups (n = 8 each): group 1 (I/R); group II morphine preconditioning (M1 ); group Ⅲ morphine postconditioning (M2); group IV M1 + M2; group V 5-hydroxydecanoate (5-HD) + M2. Group M1 was perfused with K-H solution containing morphine 3.0 μmol/L for 20 min 30 min before ischemia followed by 10 min normal K-H solution perfusion. Group M2 was perfused with K-H solution containing morphine 3.0 μmol/L for 10 min at the beginning of reperfusion followed by 50 min normal K-H solution perfusion. Group 5-HD + M2 was perfused with K-H solution containing morphine 3.0 μmol/L+ 5-HD 10-4 mmol/L for 10 min at the beginning of reperfusion followed by 50 min normal K-H solution perfusion. Myocardial CK-MB activity was measured and myocardial infarct size (IS/AAR) detennined (by 2,3,5-triphenyl tetrazolium staining) at the end of 60 min reperfusion. Results The preconditioning, postconditioning and combination of preconditioning and postconditioning with morphine 3.0 μmol/L perfusion for 10 min all provided cardio-protective effects in terms of IS/AAR and myocardial activation of CK-MB. Conclusion Although the combination of morphine preconditioning and postconditioning can protect the heart against I/R injury, the effects are similar to those of either of them alone, and the reason may be that either of them alone protects the heart against I/R injury via activating mitoKATP .

Objective To determine whether morphine postconditioning (MP) could protect the heart against ischemia reperfusion (I/R) injury and which specific type(s) of the opioid receptor is involved in the cardioprotective effect produced by hiP. Methods Male SD rots weighing 180-200 g were killed after intraperitoneal heparin 500 U/kg. The hearts were immediately removed and passively perfused in a Langendorff apparatus with K-H solution gassed with 95% O2-5% CO2. HR and left ventricular systolic pressure (LVSP) were measured from a fluid-filled latex balloon in the left ventricle. Global myocardial ischemia was induced by interrupting perfusion for 45 min followed by 60 min reperfusion. The experiment was performed in 3 parts. In Part Ⅰ 32 isolated rat hearts were randomly divided into 4 groups (n = 8 each): group Ⅰ control received no treatment; group Ⅱ ,Ⅲ,Ⅳ were first perfused with K-H solution containing morphine 0.3, 3.0 and 30 μmol/L respectively for 10 min immediately after the end of ischemia followed by 50 min normal K-H solution perfusion. In part Ⅱ,the concentration of morphine in K-H solution which provided the best cardio-protective effects was chosen according to the result of Part Ⅰ , 32 isolated rat hearts were randomly divided into 4 groups ( n = 8 each) : group Ⅰ received no treatment; gvoup Ⅱ,ⅢⅣ were first perfused with K-H solution containing morphine for 5, 10, 20 min respectively immediately after ischemia followed by 50 min peffusion with normal K-H solution. In part Ⅲ,the MP method which provided the best cardio-protective effects was chosen according to the result of Part Ⅱ , 37 isolated rat hearts were randomly divided into 5 groups: group Ⅰ control (n=8);group Ⅱ-Ⅴ were first perfused for 10 min with K-H solution containing morphine (Ⅱ,n = 8)/morphine + naloxone 10 μmol/L(Ⅲ, n = 7)/morphine + nor-binaltorphimine 5 μmol/L (specific κ receptor antagonist, n = 7)/morphine + nalu'indole 5 μmol/L (specific δ receptor antagonist, n = 7) followed by 50 min reperfusion with normal K-H solution. Myocardial CK-MB activity was measured and myocardial infarct size (IS/AAR) determined (by 2,3,5-triphenyl tetrazolium staining) at the end of 60 min reperfusion.Results The postconditioning with morphine 3.0 μmol/L perfusion for 10 min provided the best cardio-protective effects in terms of IS/AAR and myocardial release of CK-MB. Nuloxone completely abolished the cardio-protective effects of MP. Nor-binaltorphimine partly reversed the protective effect of MP, while naltrindole had no effects on MP. Conclusion MP protects the heart against I/R injury via activating κ receptor.