Cai Xu-xu, Du Yue, Gao Hong, Cui Zhen-ze, Han Yu-kun
Department of Pediatrics, The 2nd Clinical Hospital, China Medical University, Shenyang 110004, China.
Zhonghua Er Ke Za Zhi. 2003 Mar;41(3):208-11.
Neonatal asphyxia is one of the main causes for the acute respiratory distress syndrome (ARDS) in full-term newborns. Now it is believed that the reduced amount and abnormal function of pulmonary surfactant due to various causes is a major factor leading to acute lung injury. This study aimed at using an intrauterine acute ischemic-hypoxia rat model and investigating the effect of intrauterine acute ischemic-hypoxia on the expression of surfactant protein A (SP-A) and surfactant protein B (SP-B) in neonatal rat lungs.
The rat model of acute intrauterine ischemic-hypoxia was established by ligating the unilateral uterine horn vessels of Wistar rats at the 21st gestational day. While the rat pups from the other side of the uterus, of which the uterine horn vessel was not ligated, were the sham-operation group. Rat pups were delivered by cesarean section at the 20, 30 and 40 min following the ischemic-hypoxia insult. The rat pups delivered by cesarean section from the gestation of 21 days were the normal control group. There were 42 rat pups and 6 pups in each group in this study. The distribution of SP-B protein in the neonatal rat lungs of different period of ischemia was examined by using SABC method. The average gray value of SP-B staining in type II alveolar epithelial cells were measured by Universal Imaging Porporation with Meta Morph software. The reverse transcription polymerase chain reaction (RT-PCR) was performed to quantitate the expression of SP-A and SP-B mRNA.
Following the intrauterine acute ischemic-hypoxia, the numbers of type II alveolar epithelial cells with the positive SP-B staining were markedly declined. The average gray values at the 20, 30 and 40 min after the ischemia were 78.89 +/- 1.08, 79.69 +/- 0.13 and 80.00 +/- 0.63, respectively, which increased significantly compared with the normal control group (76.13 +/- 0.43, P < 0.01). The expression of SP-A and SP-B mRNA was weak following the ischemic-hypoxia insult. The relative amounts of SP-A (1.16 +/- 0.06, 1.14 +/- 0.01 and 1.13 +/- 0.04, respectively) and SP-B (0.81 +/- 0.02, 0.78 +/- 0.02 and 0.79 +/- 0.04, respectively) at the 20, 30 and 40 min after the ischemia were reduced significantly compared with controls (1.27 +/- 0.09 and 0.89 +/- 0.06, respectively, P < 0.05 and < 0.01) and reduced gradually following the prolongation of the insult. There were no significant differences (P > 0.05) between the normal and sham operation control groups on the expressions of SP-B protein as well as the SP-A and SP-B mRNA.
The reduced synthesis of SP-B protein and the reduced expression of SP-A and SP-B mRNA might be caused by intrauterine acute ischemic-hypoxia, which may support theoretically the early application of pulmonary surfactant including SP-A and SP-B for treating the lung injuries of asphyxia in newborns.
新生儿窒息是足月新生儿急性呼吸窘迫综合征（ARDS）的主要病因之一。目前认为，各种原因导致的肺表面活性物质数量减少和功能异常是引起急性肺损伤的主要因素。本研究旨在利用宫内急性缺血缺氧大鼠模型，探讨宫内急性缺血缺氧对新生大鼠肺表面活性蛋白A（SP-A）和表面活性蛋白B（SP-B）表达的影响。
在妊娠第21天结扎Wistar大鼠单侧子宫角血管，建立宫内急性缺血缺氧大鼠模型。未结扎子宫角血管的子宫另一侧的大鼠幼崽作为假手术组。在缺血缺氧损伤后20、30和40分钟通过剖宫产取出大鼠幼崽。妊娠21天剖宫产的大鼠幼崽作为正常对照组。本研究共有42只大鼠幼崽，每组6只。采用SABC法检测不同缺血时期新生大鼠肺中SP-B蛋白的分布。使用Universal Imaging Porporation公司的Meta Morph软件测量II型肺泡上皮细胞中SP-B染色的平均灰度值。采用逆转录聚合酶链反应（RT-PCR）定量SP-A和SP-B mRNA的表达。
宫内急性缺血缺氧后，SP-B染色阳性的II型肺泡上皮细胞数量明显减少。缺血后20、30和40分钟的平均灰度值分别为78.89±1.08、79.69±0.13和80.00±0.63，与正常对照组（76.13±0.43）相比显著升高（P<0.01）。缺血缺氧损伤后SP-A和SP-B mRNA的表达较弱。缺血后20、30和40分钟时SP-A（分别为1.16±0.06、1.14±0.01和1.13±0.04）和SP-B（分别为0.81±0.02、0.78±0.02和0.79±0.04）的相对含量与对照组（分别为1.27±0.09和0.89±0.06）相比显著降低（P<0.05和<0.01），且随着损伤时间的延长逐渐降低。正常对照组和假手术对照组在SP-B蛋白以及SP-A和SP-B mRNA的表达上无显著差异（P>0.05）。
宫内急性缺血缺氧可能导致SP-B蛋白合成减少以及SP-A和SP-B mRNA表达降低，这在理论上可能支持早期应用包括SP-A和SP-B在内的肺表面活性物质治疗新生儿窒息所致的肺损伤。
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