CELLULAR MECHANISMS OF ISCHEMIA PRECONDITIONING

缺血预处理（IPC）是指其中组织缺血的现象。 使其对长时间缺血的有害作用具有抗性， 通过预先暴露于短暂的血管闭塞来进行再灌注（I/R）。 虽然在十多年前首次描述，但 IPC的有益效果仍然不确定。 然而，初步数据显示， 我们的实验室表明，IPC可防止I/R诱导的肠道氧化剂 白细胞/内皮细胞相互作用和微静脉蛋白 泄漏 由于黄嘌呤产生活性氧代谢产物 肠缺血再灌注过程中的氧化酶和其他来源 启动趋化刺激的形成，诱导 内皮细胞粘附分子，并降低肠道水平的 有效的抗粘附剂一氧化氮，我们假设IPC诱导的 白细胞粘附的减少是由以下作用介导的： 预处理以减少缺血后氧化剂产生。 解决 根据这一中心假设，提出了四个具体目标。 一个目的是 确定IPC是否阻止肠系膜黄嘌呤氧化酶的增加 IPC对促炎性刺激的活性或影响 （血小板活化因子（PAF）、白三烯B4（LTB 4）、补体 激活）。 第三个具体目标是 确定IPC是否减弱了P-选择素的表达， 暴露于I/R的毛细血管后微静脉内皮。 由于有益的 IPC对缺血后肠系膜微血管功能障碍的影响 IPC期间局部应用腺苷脱氨酶可逆转，或 蛋白激酶C（PKC）抑制剂在长时间缺血期间， 第四个目标是阐明可能 参与偶联IPC和缺血后腺苷的产生 氧化剂产生、白细胞粘附和小静脉蛋白减少 泄漏 为了实现这些目标，我们将利用活体显微镜 定量氧化剂产生、白细胞/内皮细胞 相互作用和大鼠肠系膜中的小静脉蛋白渗漏。 肠系膜 黄嘌呤氧化酶、一氧化氮合酶、磷脂酶C和PKC 活动，亚硝酸盐/硝酸盐的生产，PAF和LTB 4水平，以及程度 还将评估补体激活。 体内肠系膜P- 选择素表达将使用双放射性标记的 单克隆抗体方法。 研究报告不仅要 大大提高我们对IPC机制的理解， 减少肠缺血后微血管功能障碍， 也为开发新的治疗药物提供了理论基础。 利用预适应介质的I/R干预 现象

Ischemic preconditioning (IPC) refers to a phenomenon in which a tissue is rendered resistant to the deleterious effects of prolonged ischemia and reperfusion (I/R) by prior exposure to brief periods of vascular occlusion. Although first described over a decade ago, the mechanisms underlying the beneficial effects of IPC remain uncertain. However, preliminary data from our laboratory indicates that IPC prevents I/R-induced intestinal oxidant production, leukocyte/endothelial cell interactions, and venular protein leakage. Since the production of reactive oxygen metabolites from xanthine oxidase and other sources during reperfusion of ischemic intestine initiates the formation of chemotactic stimuli, induces the expression of endothelial cell adhesion molecules, and reduces intestinal levels of the potent antiadhesive agent nitric oxide, we hypothesize that IPC-induced reductions in leukocyte adhesion are mediated by the effect of preconditioning to reduce the postischemic oxidant production. To address this central postulate, four specific aims are proposed. One aim is to determine whether IPC prevents the increase in mesenteric xanthine oxidase activity or influence of IPC on the elaboration of proinflammatory stimuli (platelet activating factor (PAF), leukotriene B4(LTB4), complement activation) in postischemic small bowel. A third specific aim is to determine whether IPC attenuates the expression of P-selectin by the endothelium in postcapillary venules exposed to I/R. Since the beneficial effects of IPC on postischemic mesenteric microvascular dysfunction are reversed by topical application of adenosine deaminase during IPC or protein kinase C (PKC) inhibitors during the period of prolonged ischemia, fa fourth aim is directed at elucidating the mechanisms that may be involved in coupling adenosine production during IPC to the postischemic reductions in oxidant production, leukocyte adhesion, and venular protein leakage. To accomplish these aims, we will utilize intravital microscopic approaches to quantitate oxidant production, leukocyte/endothelial cell interactions, and venular protein leakage in rat mesentery. Mesenteric xanthine oxidase, nitric oxide synthase, phospholipase C, and PKC activities, nitrite/nitrate production, PAF and LTB4 levels, and the extent of complement activation will also be assessed. In vivo mesenteric P- selectin expression will be quantitated using a dual-radiolabeled monoclonal antibody approach. The proposed studies should not only substantially improve our understanding of the mechanisms whereby IPC reduces postischemic microvascular dysfunction in the intestine but should also provide a rationale for the development of novel therapeutic interventions in I/R that exploit the mediators of the preconditioning phenomenon.