Objective To investigate the role of prenatal single-dose administration of dexamethasone and ambroxol on the expression of Toll-like receptor 4 (TLR4) of fetal and neonatal rats. Methods Fifty-four pregnant rats were randomly divided into three groups with eighteen rats in each group:rats treated with 0.2 mg/kg dexamethasone (group 1),0.2 mg/kg dexamethasone and 100 mg/kg ambroxol (group 2),or saline(controls) on the 17th day of gestation.The lung tissues of the offsprings were harvest independently on the 19th day of gestation,the postnatal 3 days and 7 days.The expressions of TLR4 in fetal/neonatal rat lungs of each pregnant rat were analyzed by reverse transcription-polymerase chain reaction(RT-PCR),immunohistochemistry stain,and Western blot. ANOVA and two independent samples t-test were applied. Results On the 19th day of pregnancy,TLR4 mRNA expression was up-regulated in lungs of the two treatment groups compared with controls(controls:0.26 ± 0.18,group 1:0.39 ± 0.21,t =5.866,P＜ 0.05 ; control:0.27 ± 0.22,group 2:0.46 ± 0.13,t =9.572,P＜ 0.01 ).TLR4 mRNA expression was up-regulated in group 2 compared with controls on the postnatal 3 days and 7 days(postnatal 3 d:0.59 ± 0.23 and 0.47 ±0.24,t=2.295,P＜0.05;postnatal 7 d:0.52±0.12 and 0.35±0.17,t=4.219,P＜0.05),while no significant difference was found in group 1 compared with the controls(postnatal 3 d:0.45±0.22 and 0.44±0.14,t=0.128,P＞0.05; postnatal 7 d:0.40±0.16 and 0.36 ±0.12,t=1.365,P＞0.05).Results of the immunohistochemistry demonstrated that on the 19th day of pregnancy,the protein expression of TLR4 was significantly increased in the two treatment groups (controls:0.20 ± 0.29,group 1:0.35±0.32,t=7.179,P＜0.05 ;controls:0.20±0.29,group 2:0.39±0.25,t=10.764,P＜0.01).The protein expression of TLR4 was significantly increased in group 2 on the postnatal 3 days and 7 days(postnatal 3 d:0.55±0.32 and 0.37±0.18,t=7.121,P＜0.05;postnatal 7 d:0.41±0.29and 0.25±0.24,t=6.355,P＜0.05),while no notable difference was found between group 1 and the control (postnatal 3 d:0.40±0.21 and 0.37±0.18,t=0.683,P＞0.05 ;postnatal 7 d:0.28±0.31 and 0.25±0.24,t=0.462,P＞0.05).Results of the Western blot demonstrated that on the 19th day of pregnancy,the protein expression of TLR4 was significantly increased in the two treatment groups (controls:0.15 ± 0.12,group 1:0.27± 0.20,t =7.835,P＜0.05; controls:0.16 ± 0.18,group 2:0.34±0.16,t=10.470,P＜0.01).The protein expression of TLR4 was significantly increased in lungs of the combination administration group on the postnatal 3 days and 7 days(postnatal 3 d:group 2:0.37±0.20 and 0.25±0.22,t=6.379,P＜0.05; postnatal 7 d:0.35±0.15 and 0.24±0.13,t=5.152,P＜0.05),while no notable difference could be found between group 1 and the control (postnatal3 d:0.32±0.26 and 0.25±0.16,t=1.167,P＞0.05; postnatal 7 d:0.29±0.19 and 0.24±0.10,t =1.248,P ＞ 0.05 ). Conclusions Prenatal single-dose administration of dexamethasone may up-regulate the expression of TLR4 in the rat fetal lung.The up-regulation of TLR4 might be one of the critical factors for glucocorticoid-induced maturity of fetal lung.Prenatal single-dose administration of dexamethasone and ambroxol may have effects on the regulation of TLR4 not only in fetal rats,but also in neonatal rats.