低氧对大鼠肺组织一氧化氮合酶分布及活性的影响

Effect of Hypoxia on Distribution and Activity of Nitric Oxide Synthase in Rat Lung

本研究利用低压缺氧性肺动脉高压大鼠模型，通过NADPH－d组织化学染色对肺组织一氧化氮合酶（NOS）进行定性及定位分析、并利用3H－L一精氨酸转化实验定量测定肺组织NOS的活性，以观察低氧对大鼠肺组织NOS分布及活性的影响，旨在探讨NO及NOS在缺氧性肺动脉高压形成中的作用。酶活性测定结果表明缺氧2周大鼠肺组织总NOS活性略有升高，其中原生型NOS（CNOS）活性显著降低（P＜0．05），诱生型NOS（iNOS）活性极显著升高（P＜0．01），NADPH－d染色结果显示肺血管内皮及平滑肌细胞NOS活性均明显增强。提示缺氧可能使肺血管内皮CNOS活性降低，NO生成减少，从而导致肺血管收缩反应增强，肺动脉压升高；缺氧还可能诱导肺血管内皮和平滑肌细胞iNOS表达和活性增加，在缺氧性肺血管收缩反应和结构重组中起到一定的调节作用，从而限制肺动脉压的过度升高。

Nitric oxide is an important cellular messenger molecule that has been implicated in awide range of physiological and pathophysiological actions in cardiovascular, immune, andnervous systems. Nitric oxide synthase (NOS) is the sole and key enzyme responsible for thegeneration of nitric oxide. The effect of hypoxia-induced pu1monary hypertension on NOS inthe lung is controversial. To clarify the effect of hypoxia on distribution and activity of NOSin rat lung, localization of NOS in the lungs of hypoxic and normoxic rats were studied usingNADPH-diaphorase histochemical staining techniques, NOS enzyme activity in the lung ho-mogenates was assessed by [3H] arginine to [3H] citrulline conversion- In the normoxic rat,NADPH-d was distributed in the endothelial cells of large pulmonary vessels (ID>15O pm)and medium-sized (5O um<ID<l50um) vessels but was not detected in the endothelium ofsmall vessels (IDX5O Um), and there was an absence of NADPH-d staining in the smoothmuscle cells of small, medium, and large pulmonary vessels. However, After hypoxic expo-sure for two weeks, NADPH-d staining increased dramatically in the endothelial cells oflarge and medium-sized pulmonary vessels, and NADPH-d became markedly positive in theendothelial cells of small vessels. Hypoxid was also found to induce de novo NOS expressionin the smooth muscle cells of small, medium-sized, and large pulmonary vessels. The en-zyme activity of constitutive NOS(cNOS) was decreased obviously in the hypoxic rat lungs,but that of inducible NOS(iNOS) was increased significantly in the hypoxic rat lungs. Theseresults suggested that the inhibited endothelium-derived relaxing factor (EDRF)/NO-depen-dent vasodilation after hypoxic exposure might be induced by decreased activity of cNOS inthe endothelium of pulmonary vessels, and hypoxia-induced upregulation of iNOS expressionand activity in the rat lung might play an important role in the adaptation of pulmonary circu-lation to hypoxia.