老龄大鼠脑缺血-再灌注微血管基底膜损伤变化及与纤溶酶原激活系的关系

目的研究老龄大鼠脑缺血一再灌注（I／R）不同时期微血管基底膜损伤与纤溶酶原激活系的关系。方法采用大脑中动脉阻塞（MCAO）线栓法制备大鼠局灶性脑I／R模型，将大鼠分为青年假手术组、老龄假手术组、青年模型组和老龄模型组，其中模型组又分为I3h，I／R6、12、24、72和144h各时间点组。采用免疫组化、酶谱与反向酶谱分析等方法测定各脑微血管结构、基底膜Ⅳ型胶原、层连蛋白（LN）和纤溶酶原激活系的变化。结果与青年假手术组比较，老龄假手术组Ⅳ型胶原、LN表达增强。随着I／R时间的延长，老龄与青年大鼠基底膜成分Ⅳ型胶原和LN表达递减；组织型纤溶酶原激活剂（t-PA）、尿激酶型纤溶酶原激活剂（u-PA）、纤溶酶原激活物抑制剂（PAI-1）表达水平呈先增强后降低的趋势。与青年模型组相同时间点比较，老龄模型组Ⅳ型胶原（I3h、I／R6h、I／R12h）、LN（I3h、I／R6h～24h）、t-PA（I／R6h～24h）、u-PA（I／R12h～144h）表达增强，PAI-1（I／R12h、I／R24h）表达降低，差异均有显著性。另外，PAI-1的反向酶谱分析比较，量的变化与免疫表达规律基本一致。结论随着增龄，大鼠脑微血管基底膜成分Ⅳ型胶原、LN增加。在脑I／R微血管基底膜损伤方面，老龄大鼠较青年严重，其损伤的特点与纤溶酶原激活系变化有关。

Relationship of changes in basement membrane of microvessels after cerebral ischemia/reperfusion and plasminogen activator system in aged rats

OBJECTIVE: To study the relationship of changes in basement membrane of cerebral micro-vessels and plasminogen activator system after cerebral ischemia/reperfusion (I/R) injury in aged rats. METHODS: Middle cerebral artery occlusion (MCAO) was produced by the introduction of a thread. Rats were divided randomly into sham-operation group with young rats (cerebral ischemia 3 hours and I/R 6, 12, 24, 72, 144 hours groups), sham-operation group and I/R groups in aged rats (cerebral ischemia 3 hours and I/R 6, 12, 24, 72, 144 hours groups). Immunohistochemical technique, zymogram analysis, and reverse zymogram analysis were used to study changes in basement membrane structure of cerebral-cortex microvessel, type IV collagen (Col IV) and laminine (LN) contents, and plasminogen activator system in every group. RESULTS: With the increase of age, Col IV and LN contents of the microvessel basement membrane increased. With prolongation of I/R, the contents of Col IV and LN decreased in both young and aged rats, while the contents of tissue plasminogen activator (t-PA), urokinase plasminogen (u-PA) and plasminogen activator inhibitor (PAI-1) expression increased at the beginning and decreased subsequently. Compared with young groups, Col IV (ischemia 3 hours-I/R 12 hours), LN (ischemia 3 hours-I/R 24 hours), t-PA (I/R 6-24 hours) and u-PA (I/R 12-144 hours) expression levels were higher in aged rats, but PAI-1 (I/R 12 and 24 hours) expression was lower. In addition, changes in PAI-1 contents as determined with reverse zymogram analysis method coincided with its immunoexpression. CONCLUSION: With the increase of age, alterations in constitutents of cerebro-microvessel basement membrane (Col IV and LN) increased. Injury to cerebro-microvessel basement membrane resulted in more serious changes in aged rats compared with the young rats. Changes in cerebro-microvessel basement membrane after I/R injury in the aged SD rats is related to change in plasminogen activator system.