Effects of histologic chorioamnionitis induced by lipopolysaccharide intra-amniotic injection on fetal lung maturation and development in preterm fetal rats

Abstract

Objective With various doses of lipopolysaccharide (LPS) intra-amniotic injection in pregnant rats to establish histologic chorioamnionitis (HCA) model,and to determine the effects of HCA on fetal lung maturation and development in preterm fetal rats.Methods Thirty pregnant Sprague-Dawley rats were randomly assigned to four groups.On 19 days of gestation,rats in three model groups (n=8) were given intra-amniotic injection of LPS 2,8,10 μg,respectively,and those in the only one control group (n=6)was given normal saline (NS) 40 μl.Fetal rats were taken out 48 hours after LPS injection.Placenta,fetal membrane,fetal lung and umbilical cord were collected for pathological examination.mRNAs of surfactant protein (SP)-A,B and C and keratinocyte growth factor (KGF) in lung were determined by quantitative real-time polymerase chain preaction.KGF protein expression in lung was measured by immunohistochemistry.Morphologic observation of lung was performed on postnatal day 3.R× C table Chi-square test,KruskalWallis test and analysis of variance were used as statistical methods.Results (1) Fetal rat mortality in control,LPS2,LPS8 and LPS10 group was 0.0％ (0/55),22.5％ (18/80),51.4％ (36/70) and 87.5％(35/40),respectively,which increased with increasing dose of LPS (x2=46.183,P＜0.005).(2) HCA,fetal lung inflammation and umbilical vasculitis were induced in LPS groups,and the severity was dosedependent (fetal lung inflammation:Hc=39.84,HCA:Hc=41.13,umbilical vasculitis:Hc=41.52,all P＜0.01).(3) The expression of SP-A,SP-B,SP-C and KGF mRNAs in the four groups (control,LPS2,8,10) had statistical differences (SP-A mRNA:0.99±0.28,2.48±0.34,1.09±0.31 and 0.09±0.09,F=78.051; SP-B mRNA:0.99±0.34,2.23±0.53,1.49±0.51 and 0.14±0.06,F=28.327; SP-C mRNA:1.20±0.39,2.00±0.20,1.04±0.37 and 0.12±0.16,F=39.546; KGF mRNA:0.97±0.19,2.18±0.61,0.93±0.09 and 0.21±0.11,F=37.544; all P＜0.01).All mRNA expressions in LPS2 group were higher than those in the control group and those in LPS10 group was lower (all P＜0.05).(4) The expression of KGF protein in LPS2 group was significantly higher than that in other groups (0.60±0.20 vs 0.28±0.12,0.37±0.22,0.24±0.12,F=17.280,all P＜0.01).(5) Alveolarization was significantly inhibited in LPS8 group on postnatal day 3,and less maturity of pulmonary tissue was observed.Conclusions Various doses of LPS intra-amniotic injection in rats could induce HCA,fetal lung inflammation and umbilical vasculitis with different degrees.Histological inflammation would be worse with increasing LPS dosage.Moderate inflammation could promote lung maturation without inducing bronchopulmonary dysplasia,and KGF may play a role in this process. Key words: Chorioamnionitis; Infant, premature; Lung; Fetal organ maturity; Fibroblast growth factor7; Disease models, animal; Lipopolysaccharides