一氧化氮降低失血性休克血管反应性的机制

Mechanism of vascular hyporeactivity induced by NO in hemorrhagic shock

目的 :探讨NO在失血性休克血管低反应性发生中的作用机制和防治。方法 :复制SD大鼠失血性休克模型 ,测定脊斜肌微动脉对去甲肾上腺素 (NE)的反应性。休克至血管反应性下降时 ,用同位素标记底物法测定脏器中NOS活性 ;分离肠系膜细动脉血管平滑肌细胞 (ASMC) ,用荧光探针和共聚焦显微镜测定NO底物左旋精氨酸 (L -Arg)和诱导性NOS(iNOS)抑制剂氨基胍 (AG)对膜电位的影响 ;回输全部失血同时给L -Arg和AG观察其对大鼠 2 4h存活率的影响。结果 :休克至血管反应性降低时 ,心、肝NOS活性增加。L -Arg对对照组大鼠ASMC的膜电位无影响 ,但可使反应性低下大鼠的ASMC超极化 ;用AG预处理ASMC ,则降低L -Arg引起的超极化幅度。回输全部失血时给AG可增加大鼠 2 4h存活率。结论 :HS后期ASMC中iNOS激活导致NO产生增加 ,并引起ASMC超极化可能是失血性休克后期血管低反应性发生的机制之一。

AIM: To investigate the role of nitric oxide (NO) in vascular hyporeactivity during prolonged hemorrhagic shock (HS). METHODS: Anesthetized Sprague-Dawley rats (180-220 g) were subjected to HS insult in which they were bled to a mean arterial pressure (MAP) of 40 mmHg (5.33 kPa) and arteriolar reactivity to norepinephrine in spinotrapezius was detected. The constant MAP of 40 mmHg was maintained until vascular hyporeactivity had occurred and then were resuscitated or sacrificed for further analysis. NO synthase (NOS) activity was measured ex vivo by the conversion of [3H]-arginine to [3H]-citrulline in homogenates from heart, lung, liver, spleen, duodunum, skeletal muscle. 24 h survival rates of resuscitated rats were observed with and without administration of aminoguanidine (AG), a selective inducible NOS (iNOS) inhibitor. Mesenteric arteriolar smooth muscle cells (ASMC) were isolated, and the effects of L-arginine (L-Arg) on membrane potential (MP) of ASMC were determined by fluorescent probe and confocal microscopy in the absence and presence of AG. RESULTS: When vascular hyporeactivity occurred, an increase of NOS activity was observed in liver and heart. Resuscitated rats with AG had a higher survival rate compared with that of control. The MP of ASMC was decreased (more negative) immediately following the addition of L-Arg, and the hyperpolarization effects of L-Arg were partially blocked in the presence of AG. CONCLUSION: These results suggest that excessive NO produced in HS is responsible for the occurrence of vascular hyporeactivity in prolonged hemorrhagic shock, and one of the mechanisms of which may be hyperpolarization of ASMC caused by NO.