CELLULAR MECHANISMS OF ISCHEMIA PRECONDITIONING

缺血预适应(IPC)指的是一种组织被 能抵抗长时间缺血的有害影响 再灌注(I/R)，预先暴露于短暂的血管闭塞状态。 虽然最早是在十多年前描述的，但背后的机制 IPC的有利影响仍不确定。然而，来自 我们的实验室表明，IPC可以预防I/R诱导的肠道氧化剂 产生、白细胞/内皮细胞相互作用和小静脉蛋白 漏水。自黄嘌呤产生活性氧代谢物以来 缺血肠再灌流过程中的氧化酶及其他来源 启动趋化刺激的形成，诱导表达 内皮细胞黏附分子，并降低肠道中 强大的抗黏附剂一氧化氮，我们假设IPC诱导 白细胞粘附性的减少是通过以下作用介导的 预适应以减少缺血后氧化剂的产生。致信地址 在这一中心假设下，提出了四个具体目标。一个目标是 确定IPC是否能阻止肠系膜黄嘌呤氧化酶的增加 IPC在促炎刺激的形成中的活性或影响 (血小板活化因子(PAF)、白三烯B4(LTB4)、补体 缺血后小肠的激活)。第三个具体目标是 确定IPC是否通过抑制P-选择素的表达 缺血再灌注对毛细血管后小静脉内皮细胞的影响 缺血预适应对缺血后肠系膜微血管功能障碍的影响 在IPC期间局部应用腺苷脱氨酶逆转 蛋白激酶C(PKC)抑制剂在长时间的缺血期间， FA的第四个目标是阐明可能存在的 参与IPC期间腺苷产生与缺血后的偶联 减少氧化剂产生、白细胞黏附和小静脉蛋白 漏水。为了实现这些目标，我们将利用活着的显微镜 定量氧化剂产生、白细胞/内皮细胞的方法 相互作用与大鼠肠系膜微静脉蛋白渗漏。肠系膜 黄嘌呤氧化酶、一氧化氮合酶、磷脂酶C和蛋白激酶C 活动、亚硝酸盐/硝酸盐的产生、PAF和LTB4水平以及程度 还将评估补体激活的程度。活体肠系膜P- 选择素的表达将使用双标记法进行定量 单抗方法。拟议的研究不仅应该 大大提高我们对IPC的机制的理解 减少缺血后肠道微血管功能障碍，但应该 也为开发新的治疗方法提供了理论基础 利用预适应调节因子的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.