AIM : To evaluate the effects of prenatal dexamethasone( DXM ) exposure on growth and lung maturation in rats.METHODS: Twenty - four pregnant Sprague - Dawley( SD ) rats were divided into 3 groups: 8 pregnant rats in antenatal thrice - DXM group were injected intramuscularly with DXM( 0.8 mg · kg-1 · day -1 ) for 3 consecutive days( on gestational day 18 , 19 and 20 ) ; 8 pregnant rats in antenatal once - DXM group were injected intramuscularly with DXM on gestational day 19.The control rats received equivalent volume of isotonic saline at the same time points.The lungs of the newborn rats on day 1, 4, 10 and 14 were examined.The tissue sections were prepared with HE staining for morphological investigation under light microscope.The data analysis was performed by means of a digital image analysis system, including thickness of interalveolar walls. alveolar( saccules ) areas, the number of air spaces, the number and length of secondary septa, and the surface densities of the air spaces.Transmission electronic microscope was used to observe the basement membrane of the lung epithelial cells.RESULTS: In control group, and thickness of interalveolar walls, smaller alveolar( saccules ) area, increased surface area/volume and number of air spaces were observed from day 1to day 14.On day 4, an appreciahle number of sprouting crests appeared, then the number and length of secondary septa increased until day 14.In antenatal thrice - DXM group, the air spaces were larger, and the thickness of intersaccular walls were thinner as compared to saccules of the control rats on day 1( P ＜0.01 , P ＜0.05 ).There were thinner inter air space septa( P ＜ 0.05 ) , larger and fewer air spaces, and a reduction in the number of sprouting secondary septa on day 4, 10 and 14 than those in the control rats with significant differences( P ＜0.01 ).In antenatal once - DXA group, intersaccular walls were thinner than those in the control rats with significant differences( P ＜ 0.05 ).The results of electron microscopy revealed that the basement membrane of lung epithelial cells turned thin and discontinuous on day 1 and day 4in the control rats, resulting in the close contact between epithelial cells and fibroblasts.In antenatal thrice - DXN group,the discontinuous basement membrane and close c:ontact of the cells were seldom seen.CONCLUSION : Antenatal thrice - injec:tion of DXM applied on gestational day 18, 19 and 20 impairs the alveoli formation in newhorn rats.Antenatal once - injection of DXM has no remarkable effect on postnatal alveolarization.%目的:探讨孕期肌注不同剂量地塞米松对新生鼠肺泡成熟的影响.方法:24只SD孕大鼠分为对照组、产前1次注射组(孕19 d肌注地塞米松0.8 mg·kg-1·d-1)和产前3次注射组(孕18、19、20 d均肌注地塞米松 0.8 mg·kg-1·d-1),每组8只,取新生1、4、10、14 d鼠肺,病理切片,HE染色,观察肺泡形态学的改变,计算机图像分析.电镜检查观察产前3次注射组和对照组肺上皮细胞基底膜的连续性.结果:对照组从1-14日龄鼠肺泡间隔渐变薄,肺泡面积变小,肺泡表面积/肺泡体积(S/V)增大,肺(囊)泡数渐增多,4日龄鼠肺次级隔开始长出,至14日龄隔数目渐增多.产前3次注射组的1日龄囊泡隔变薄,肺囊泡面积增大,差异非常显著(P＜0.01),肺囊泡数明显减少(P＜0.05);4、10、14日龄肺泡间隔明显变薄(P＜0.05),肺泡明显增大,S/V较对照组小,肺囊泡数明显减少,次级隔的长出减少,相对较短,数目较少,差异非常显著(P＜0.01).产前1次注射组1日龄鼠的肺泡间隔厚度较对照组变薄,差异显著(P＜0.05).电镜检查发现,正常1、4日龄鼠外周肺上皮细胞基底膜变薄,多处不连续,上皮细胞与成纤维细胞靠近、接触.产前3次注射组肺上皮细胞基底膜的不连续现象较少,上皮间质的直接接触较少.结论:产前3次注射地塞米松影响新生鼠肺泡形态发育,产前1次注射地塞米松对新生鼠肺泡形态发育影响不大.
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