目的：探讨反搏治疗失血休克中一氧化氮合酶（ＮＯＳ）的变化。方法：复制狗的失血休克模型，用同位素方法测定反搏前后各组织的ＮＯＳ活性。结果：体外反搏后平均动脉压较反搏前明显上升（Ｐ＜００１）。脑ＮＯＳ测定值假手术对照组明显高于失血休克组Ｐ＜００１）及失血休克克反搏组（Ｐ＜００１），失血休克组则明显低于失血休克反搏组（Ｐ＜００１）；心肌ＮＯＳ活性假手术对照组与失血休克反搏组均明显高于失血休克组（Ｐ＜００５，Ｐ＜００１），但假手术对照组与失血休克反搏组之间无显著差异（Ｐ＞００５）；主动脉ＮＯＳ活性假手术对照组明显高于失血休克组（Ｐ＜００１）及失血休克反搏组（Ｐ＜００５），但失血休克组与失血休克反搏组间无明显差异（Ｐ＞００５）。结论：体外反搏可以增强小血管ＮＯＳ活性，ＮＯＳ活性的恢复则可能在反搏治疗中起重要作用 Objective: To investigate the changes of nitric oxide synthase (NOS) in patients with counterpulsation of hemorrhagic shock. Methods: The model of hemorrhagic shock was replicated in dogs. The NOS activity of each tissue before and after the counterpulsation was measured by isotope method. Results: The mean arterial pressure after cardiopulmonary bypass was significantly higher than that before the counterpulsation (P <001). The brain NOS was significantly higher in the sham-operation control group than in the hemorrhagic shock group (P <001) and in the hemorrhagic shock group (P <001), while in the hemorrhagic shock group was significantly lower than that in the hemorrhagic shock group (P < 001). The activity of NOS in sham operation group and hemorrhage shock counterpulsation group were significantly higher than that in hemorrhagic shock group (P <005, P <001), but sham operation group and hemorrhagic shock counterpulsation group (P> 005). The aortic NOS activity in the sham operation group was significantly higher than that in the group of hemorrhagic shock (P <001) and the group of hemorrhagic shock (P <005), but the blood loss There was no significant difference between shock group and hemorrhagic shock counterpulsation group (P> 005). Conclusion: Extracorporeal counterpulsation can enhance the activity of small blood vessels and NOS activity may play an important role in counterpulsation