| Background: Myocardial ischemia reperfusion injury continues to occur after cardiac operations that have been performed in a technically adequate manner. This injury contributes significantly to postoperative morbidity and mortality, despite meticulous adherence to presently known principles of myocardial protection. A great deal of accumulated evidences implicate opening of mitochondrial ATP-sensitive potassium channel as an important step in heart protection, and have become a new target in this field. Recent studies reveal that: injury of mitochondrial and endothelial cell play an important role in heart injury. Ischemia and reperfusion during cardiac operations cause structure damage and dysfunction of mitochondrial and endothelial cell, which lead to injury of myocardium. Therefore protection on mitochondrial and endothelial cell can alleviate injury of myocardium. To investigate the cardioprotective effect of opening mitochondrial ATP-sensitive potassium channel on ischemia reperfusion heart, we established isolated rat heart Langendorff model and isolated working heart model, with which the injury of mitochondrial and endothelial cell and the injury of myocardium tissue were measured. Methods: Isolated rat heart Langendorff model and isolated working heart model were established. The study consisted of three parts: In the first part, fifty rats were divided into 5 groups randomly. Isolated rat heart Langendorff model was established. Control group (B) underwent 30-minute ischemia and 30minute reperfusion. Group C and D were treated with st.Thomas Ⅱcardioplegia, Diazoxide+ st.Thomas Ⅱcardioplegia before ischemia respectively. And group E was treated with glibenclamide, 10min before Diazoxide+ st.ThomasⅡcardioplegia. The grafts received immunohistochemical and histopathological examinations to examine the content of cytochrome and the injury of mitochondrial. The activity of cytochrome oxidase, H+-ATP and the content of ATP were evaluated too. The expression of cytochrome oxidase mRNA was evaluated by reverse transcription poiymereise chain reaction. Radioimmunoassay and multimedia pathology imaging analysis system were used for quantitative measurement of malondialdehyde. In the second part, Fifty rabbits were divided into 5 groups randomly. Isolated rat heart Langendorff model is established. Control group (B) underwent 30-minute ischemia and 30minute reperfusion. Group C and D were treated with st.ThomasⅡcardioplegia contain blood, Diazoxide+ st.ThomasⅡcardioplegia contain blood before ischemia respectively. And group E was treated with glibenclamide, 10min before Diazoxide + st.ThomasⅡcardioplegia contain blood. Harvested hearts received immunohistochemical and histopathological examinations to examine the expression of intercellular adhesion molecule-1 and endothelial cell injury. The expression of intercellular adhesion molecule-1 mRNA was evaluated by reverse transcription poiymereise chain reactio.Radioimmunoassay were used to examine the expression of tumor necrosis factor -α, endothelin -1, nitric oxide, platelet activating factor and myeloperoxidase. And multimedia pathology imaging analysis system was used for quantitative measurment intercellular adhesion molecule-1 expression. Coronary artery fluence was collected. In the third part, fifty rats were divided into 5 groups randomly. Isolated working rat heart model is established. Control group (B) underwent 30-minute ischemia and 30minute reperfusion. Group C and D were treated with st.ThomasⅡcardioplegia, Diazoxide+ st.ThomasⅡcardioplegia before ischemia respectively. And group E was treated with glibenclamide, 10min before Diazoxide+ st.Thomas Ⅱcardioplegia. At the end, HP, LVPSP , LVEDP, +dp/dtmax and -dp/dtmax were evaluated. Harvested hearts received histopathological examinations to examine the heart injury. Results: 1. Compared with the controls, the levels of cytochrome oxidase and its mRNA, H+-ATP, ATP content were significantly decreased (p <0.01), which significantly increased in group C and E(p <0.01) and increased further by treating with Diazoxide (p <0.05). At the same time, malondialdehyde and cytochrome content were significantly increased (p <0.01), which significantly decreased in group C and E(p <0.01). 2. During ischemia and reperfusion, the structure mitochondrial damaged heavily, which relived by Diazoxide.3. Compared with the controls, the levels of intercellular adhesion molecule-1 and its mRNA, tumor necrosis factor -α, endothelin -1, and myeloperoxidase. were significantly increased, which significantly decreased in group C and E(p <0.01) and decreased further by treating with Diazoxide (p <0.05). In group B, the levels of nitric oxide and coronary artery fluence decreased (p <0.01), which significantly decreased by treating with Diazoxide (p <0.05). 4. During ischemia and reperfusion, the structure mitochondrial damaged heavily, which relived by Diazoxide. 5. Compared with the controls, the levels of +dp/dtmax and -dp/dtmax and heart function were significantly decreased ( p <0.01). The cardiac tissue damaged. In group D, treated with Diazoxide the heart was protected effectively. Conclusion: 1. In this study, we established isolated rat heart Langendorff model and isolated working heart model, which is very convenient and stable. 2. During ischemia and reperfusion, the structure and function of mitochondrial damaged heavily, which can be relived by Diazoxide. 3. During ischemia and reperfusion, the structure and function of endothelial cell damaged heavily, which can be relived by Diazoxide. 4. During ischemia and reperfusion, the structure of the heart damaged, and the function decreased, which can be improved by Diazoxide. Conclusion: These results suggest that diazoxide has a cardioprotective effect on tissue and function of the heart during ischemic and reperfusion in rats.
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