持续高氧暴露降低新生大鼠肺组织血管内皮生长因子的表达

目的：高氧肺损伤是导致支气管肺发育不良(BPD)的最常见原因。血管内皮生长因子(VEGF)在新生肺中具有促进内皮细胞增殖、分化、诱导血管发生的作用。本研究动态观察高氧暴露对新生鼠肺组织VEGF表达的影响,探讨BPD的发生机制。方法：新生Wistar大鼠出生后随机分为空气组和高氧组(均n=30)。高氧组在生后12h内开始,予以持续吸入95%氧气。分别于生后1、2、3、7、14、21d各处死5只大鼠,留取肺组织标本。苏木精-伊红染色观察病理改变,免疫组化检测VEGF蛋白表达,原位杂交方法检测VEGFmRNA表达。结果以切片视野灰度值表示,值越高说明蛋白或mRNA表达越少。结果：新生鼠高氧暴露7d后肺泡间隔减少,肺微血管发育异常,间质纤维化,且病变随高氧暴露时间延长而加重。高氧组大鼠第3,7天时肺组织VEGF蛋白表达明显低于相应空气对照组(81.9±0.8vs80.8±1.0,82.8±1.2vs79.2±1.6,均P<0.01)。VEGFmRNA表达亦显著减少(89.5±1.1vs88.0±1.0,91.1±1.5vs87.7±1.7,均P<0.001)。随着暴露时间的延长,VEGF蛋白和mRNA进行性降低,在高氧暴露14、21d时几乎检测不到VEGF蛋白和mRNA的表达。结论：高氧暴露抑制新生鼠肺VEGF的表达,这可能与高氧诱导BPD的发生有关。

Exposure to prolonged hyperoxia decreases the expression of vascular endothelial growth factor in lungs of neonatal rats

OBJECTIVE: Hyperoxia-induced lung injury is the most common cause of bronchopulmonary dysplasia (BPD) in neonates. Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen that can regulate proliferation, differentiation and angiogensis of endothelial cells in neonatal lungs. This paper aimed to study the changes of VEGF expression in the lungs of neonatal rats exposed to prolonged hyperoxia so as to explore the mechanism of BPD. METHODS: Wistar rat pups were randomized to hyperoxia (Hyperoxia group, FiO_2=0.95) or room air exposure (Normoxia group) (both n=30) from postnatal 12 hrs. The rats were sacrificed at postnatal days 1, 2, 3, 7, 14 and 21 (5 rats each time point) and their lungs were collected. The lung sections were stained with hematoxylin and eosin for histological evaluation. Expressions of VEGF protein and mRNA were detected by immunohistochemistry and in situ hybridization. Results were expressed as gray values. The higher the value, the lower the expressions. RESULTS: After being exposed to hyperoxia for 7 days, lung tissues developed interstitial fibrosis, abnormal vascular constitution and a decreased alveolar septation. These changes became more obvious with the time of prolonged hyperoxia exposure. Expressions of VEGF protein at 3 and 7 days of exposure in the Hyperoxia group decreased significantly as compared with the Normoxia group (81.9±0.8 vs 80.8±1.0,82.8±1.2 vs 79.2±1.6,P<0.01). The expression of VEGF mRNA in the Hyperoxia group was also lower at 3 and 7 days of exposure (89.5± 1.1 vs 88.0±1.0, 91.1±1.5 vs 87.7±1.7, P<0.001). Both VEGF protein and mRNA levels gradually decreased with the hyperoxia exposure time and their levels could not be detected at 14 and 21 days of hyperoxia exposure. CONCLUSIONS: Hyperoxia exposure inhibited the expression of lung VEGF in neonatal rats, which may be the underlying mechanism of hyperoxia-induced BPD.