目的：研究ＮＯ合酶在肝癌发生过程中的表达与改变。方法：以化学致癌剂２－ＦＡＡ喂饲ＳＤ大鼠，对鼠肝细胞在癌变过程中的组织学改变、一氧化氮合酶（ＮＯＳ）的表达和动态变化进行了研究。结果：当肝细胞轻度损伤时，肝组织中ＮＯＳ活性与对照组相比明显下降；当肝细胞表现为癌前病变和肝细胞完全癌变时，肝组织中ＮＯＳ的合成增加其比活性仍低于正常对照鼠；肝组织中ＮＯＳ与ＮＯ水平呈明显正相关（ｒ＝０５７，Ｐ＜００１），而与总ＲＮＡ浓度无相关性。结论：研究资料提示ＮＯＳ在诱癌早期的表达处于抑制状态以对肝细胞起保护作用；而肝癌形成阶段，ＮＯＳ加速表达以杀伤肿瘤细胞 Objective: To study the expression and change of NO synthase in the process of liver cancer. METHODS: SD rats fed with chemical carcinogen 2-FAA were studied for histological changes, expression and dynamic changes of nitric oxide synthase (NOS) during the process of carcinogenesis. RESULTS: When liver cells were mildly injured, the NOS activity in liver tissue was significantly decreased compared with the control group. When the hepatocytes showed precancerous lesions and complete hepatocellular carcinoma, the synthesis of NOS in the liver tissue increased its specific activity and remained low. In normal control mice, the NOS and NO levels in liver tissue were positively correlated (r=057, P<001), but not correlated with total RNA concentration. CONCLUSIONS: The data suggest that NOS is inhibited in the early stage of carcinogenesis to protect the hepatocytes; while in the stage of liver cancer, NOS is accelerated to kill tumor cells.