LIVER PROTECTION AGAINST ISCHEMIAJREPERFUSION INJURY BY ISCHEMIC PRECONDITIONING

短暂的缺血后再灌注使组织抵抗随后的长时间缺血，这种现象称为缺血预处理。我们之前的研究表明，缺血预处理可以减少缺血/再灌注后的窦内皮细胞损伤和库普弗细胞活化，从而提高肝移植受者的存活率。缺血预处理的心脏保护作用虽然在几小时内消失，但在缺血预处理后24-48小时内再次出现，称为晚期预处理。由于后期预处理具有多种心脏保护作用，且持续时间较早期预处理长，其临床疗效近年来受到关注。因此，我们着手调查晚期预处理是否在肝脏中起作用，并阐明，如果它起作用，其机制。将肝动脉和门静脉夹入肝正中叶和左叶，诱导大鼠肝脏缺血再灌注损伤。测定血清ALT、LDH活性，评价肝细胞损伤程度。在初步实验中，我们首先确定合适的缺血时间和评价时间。将肝动脉、门静脉夹持于正中叶和左叶10分钟，再灌注10分钟，进行缺血预处理。缺血预处理可减轻缺血60分钟和再灌注180分钟后的肝损伤。缺血预处理后2小时诱导缺血再灌注损伤时，其保护肝脏的作用消失。然而，与未预处理组相比，缺血预处理后24小时引起的缺血/再灌注损伤减少。我们目前正在开展使用腺苷拮抗剂的实验，以研究腺苷受体对晚期预处理发展的贡献。

Brief periods of ischemia followed by reperfusion render tissues resistant against subsequent prolonged ischemia, a phenomenon called ischemic preconditioning. We previously showed that ischemic preconditioning decreased sinusoidal endothelial cell injury and Kupffer cell activation after ischemia/reperfusion with the consequence of improved survival of liver transplant recipients. Although cardioprotective effect of ischemic preconditioning disappears within a few hours, the effect appears again 24-48 hours after ischemic preconditioning, which is called late preconditioning. Since the late preconditioning shows various cardioprotective effects and lasts longer than the early preconditioning, its clinical efficacy is recently drawing attention. Thus we set out to investigate whether late preconditioning works in the liver or not, and to elucidate, if it works, its mechanisms. Ischemia/reperfusion injury was induced in rat livers by clamping hepatic artery and portal vein into the median and left lobes. To evaluate hepatocyte injury, serum activities of ALT and LDH were determined. At first, we decided appropriate ischemic time and the timing of evaluation in the preliminary experiments. Ischemic preconditioning was performed by clamping the hepatic artery and portal vein into the median and left lobes for 10 minutes followed by 10 minutes reperfusion. Ischemic preconditioning reduced liver injury after 60 minutes ischemia and 180 minutes reperfusion. When ischemia/reperfusion injury was induced at 2 hours after ischemic preconditioning, the hepatoprotective effect disappeared. However, ischemia/reperfusion injury induced 24 hours after ischemic preconditioning was reduced compared to no preconditioning group. We are now launching the experiments using adenosine antagonists to investigate the contribution of adenosine receptors to the development of late preconditioning.