Cote C G, Yu F S, Zulueta J J, Vosatka R J, Hassoun P M
Department of Medicine, New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
Am J Physiol. 1996 Nov;271(5 Pt 1):L869-74. doi: 10.1152/ajplung.1996.271.5.L869.
We have previously shown that nitric oxide (NO) donors, such as nitrosoglutathione, inhibit endothelial cell (EC) xanthine dehydrogenase (XD)/xanthine oxidase (XO) activity. The purpose of this study was to assess whether endothelial-derived NO plays any role in the regulation of intracellular XD/XO. We exposed rat pulmonary microvascular EC to L-arginine (precursor of NO) or inhibitors of nitric oxide synthase (NOS), i.e., NG-nitro-L-arginine methyl esther (L-NAME) and NG-nitro-L-arginine, in conditions of normoxia, hypoxia, and hypoxia followed by reoxygenation. Hypoxia alone caused a 1.9- and a 6.6-fold increase in XO and a 5-fold increase in XO + XD activities after 24 and 48 h of exposure, respectively. The combination of hypoxia and L-NAME (300 microM) treatment amounted at 48 h to a 10- and 7.5-fold increase in XO and XO + XD activities, respectively, compared with normoxic untreated cells. L-NAME also prevented the decline in XD/XO activity that occurred in untreated EC after hypoxia-reoxygenation. On the other hand, treatment with L-arginine caused a dose-dependent decrease in XD/XO activity in hypoxic EC compared with cells provided with L-arginine-free medium. In separate experiments, we assessed the role of L-arginine supplementation on the in vivo regulation of lung XD/XO by exposing male adult Sprague-Dawley rats for a period of 5 days to a hypoxic hypobaric atmosphere (0.5 atm). Exposure to hypoxia produced a significant increase in lung tissue XO activity and an increase in the ratio of XO to XD. L-Arginine supplementation in the drinking water prevented the increase in lung XO and the XO-to-XD ratio in hypoxic rats and caused a significant decrease in XO and XD in rats exposed to normoxia. In conclusion, this study suggests that endogenous NO has a significant role in the regulation of XD/XO both in vitro and in vivo. By inhibiting XD/XO activity, NO may have a modulating effect in conditions of hypoxia and hypoxia-reoxygenation, where this enzyme is thought to be important.
我们之前已经表明，一氧化氮（NO）供体，如亚硝基谷胱甘肽，可抑制内皮细胞（EC）的黄嘌呤脱氢酶（XD）/黄嘌呤氧化酶（XO）活性。本研究的目的是评估内皮源性NO在细胞内XD/XO的调节中是否起作用。我们将大鼠肺微血管内皮细胞暴露于L-精氨酸（NO的前体）或一氧化氮合酶（NOS）抑制剂，即NG-硝基-L-精氨酸甲酯（L-NAME）和NG-硝基-L-精氨酸，分别处于常氧、缺氧以及缺氧后复氧的条件下。单独缺氧在暴露24小时和48小时后，分别使XO活性增加1.9倍和6.6倍，使XO + XD活性增加5倍。与未处理的常氧细胞相比，缺氧和L-NAME（300 microM）联合处理48小时后，XO和XO + XD活性分别增加10倍和7.5倍。L-NAME还可防止缺氧复氧后未处理的内皮细胞中XD/XO活性的下降。另一方面，与无L-精氨酸培养基培养的细胞相比，用L-精氨酸处理导致缺氧内皮细胞中XD/XO活性呈剂量依赖性降低。在单独的实验中，我们通过将成年雄性Sprague-Dawley大鼠暴露于低氧低压环境（0.5个大气压）5天，评估了补充L-精氨酸对肺内XD/XO体内调节的作用。暴露于缺氧环境会使肺组织XO活性显著增加，且XO与XD的比值升高。在饮用水中补充L-精氨酸可防止缺氧大鼠肺内XO增加以及XO与XD的比值升高，并使暴露于常氧环境的大鼠的XO和XD显著降低。总之，本研究表明内源性NO在体外和体内对XD/XO的调节中均起重要作用。通过抑制XD/XO活性，NO可能在缺氧和缺氧复氧情况下发挥调节作用，而在这些情况下该酶被认为是重要的。
