Zhu Yanli, Ohlemiller Kevin K, McMahan Belinda K, Park Tae Sung, Gidday Jeffrey M
Department of Neurosurgery, Washington University School of Medicine, Box 8057, 660 S. Euclid Ave., St Louis, MO 63110, USA.
Exp Eye Res. 2006 Jan;82(1):153-63. doi: 10.1016/j.exer.2005.06.005. Epub 2005 Jul 20.
Profound morphologic and functional protection against retinal ischemic injury can be achieved if the tissue is 'preconditioned' one day earlier with a brief, noninjurious ischemic challenge. To begin to address the mechanistic basis of this 'ischemic tolerance', we used genetic and pharmacologic approaches to test the hypothesis that nitric oxide (NO) derived from one of the three NO synthase (NOS) isoforms was responsible for triggering the adaptive response to brief preconditioning ischemia. Retinae of adult mice were preconditioned with 5-min preconditioning ischemia and subjected to 45-min injurious ischemia 24 hr later. Some animals were treated with the constitutive NOS inhibitor L-nitroarginine (5 mg/kg, i.p.) 1 hr before preconditioning. Retinal layer thicknesses and cell counts were determined one week postischemia in 5-mum thin sections, and flash electroretinograms were obtained at 1 and 7 days postischemia. We confirmed that ischemic preconditioning afforded morphologic and functional protection in the strains of wild-type mice studied. Histopathologic analyses of inducible NOS (iNOS) knockout mice revealed that ischemic preconditioning was completely effective, whereas ischemic tolerance was not achieved in the retinae of endothelial NOS (eNOS) and neuronal NOS (nNOS) knockout mice. The participation of the constitutive NOS enzymes in preconditioning-induced tolerance was confirmed by the finding that administration of the NOS inhibitor L-NA to wild-type mice prior to ischemic preconditioning blocked the development of ischemic tolerance. These cross-validating genetic and pharmacologic findings indicate that NO derived from both eNOS and nNOS is a required molecular signal in the adaptive response to ischemic preconditioning in the retina.
如果在一天前用短暂的、非损伤性的缺血刺激对组织进行“预处理”，就可以对视网膜缺血损伤实现深度的形态学和功能保护。为了探究这种“缺血耐受”的机制基础，我们采用遗传学和药理学方法来检验以下假设：三种一氧化氮合酶（NOS）同工型之一产生的一氧化氮（NO）负责触发对短暂预处理缺血的适应性反应。成年小鼠的视网膜先接受5分钟的预处理缺血，24小时后再接受45分钟的损伤性缺血。一些动物在预处理前1小时腹腔注射组成型NOS抑制剂L-硝基精氨酸（5毫克/千克）。在缺血一周后，对5微米厚的切片测定视网膜各层厚度和细胞数量，并在缺血后1天和7天记录闪光视网膜电图。我们证实，缺血预处理在所研究的野生型小鼠品系中提供了形态学和功能保护。对诱导型NOS（iNOS）基因敲除小鼠的组织病理学分析表明，缺血预处理完全有效，而在内皮型NOS（eNOS）和神经元型NOS（nNOS）基因敲除小鼠的视网膜中未实现缺血耐受。在缺血预处理前给野生型小鼠施用NOS抑制剂L-NA可阻断缺血耐受的发展，这一发现证实了组成型NOS酶参与预处理诱导的耐受。这些相互验证的遗传学和药理学研究结果表明，来自eNOS和nNOS的NO是视网膜对缺血预处理适应性反应中所需的分子信号。
