Objective To explore the lung developmental disorder of rats with gestational diabetes mellitus (GDM) via investigating the GDM rat fetal lung structures and expression of pulmonary surfactant proteins (SP)-B,SP-C,thyroid transcription factor (TTF)-1 and pleiomorphic adenoma gene like (PLAGL)-2.Methods Sprague-Dawley rats were used to construct the GDM model.Twenty GDM rats were used as GDM group and 20 normal pregnant rats as control group.Cesarean section was performed on day 21 of gestation and random blood sugar was detected,and fetal rats were counted and weighed.Ultrastructure of the fetal lungs was studied by transmission electron microscopy.Sixty fetal rats were selected randomly in each group,and 360 paraffin sections were made from fetal lungs.One hundred discontinuous paraffin sections were picked up in each group to observe morphological and structural changes under optical microscope.The other one hundred discontinuous paraffin sections were picked up in each group to detect the location and expression of SP-B,SP-C,TTF-1 and PLAGL-2 protein by immunohistochemistry.Nine fetal rats were selected randomly to detect the expression level of SP-B,SP-C,TTF-1 and PLAGL-2 proteins in fetal lung tissues by Western blotting.Twenty seven fetal rats were selected randomly to detect the mRNAs level of SP-B,SP-C,TTF-1 and PLAGL-2 by real-time quantitative polymerase chain reaction.Independent sample t-test was used for statistical analysis.Results The average random blood glucose level in GDM group was significantly higher than that in control group [(26.8± 2.8) vs (4.9± 0.5) mmol/L,t=-34.05,P=0.00].The average weight of fetal rats in GDM group was higher than that in control group [(5.6±0.6) vs (5.2±0.5) g,t=-1.97,P=0.03].Alveolar number (10.1 ± 1.6 vs 12.1 ± 1.3) and alveolar area [(986.9 ± 5.5) vs (1 257.3± 5.0) μ m2] in GDM group was less than that in control group (t=9.84 and 27.53,both P ＜ 0.05).Alveolar septum [(11.5±6.2) vs (9.9±4.3) μm] in GDM group was higher than that in control group (t=-2.17,P ＜ 0.05).Microvillus in type] cells were short and the number of lamellar bodies was significantly decreased in GDM group.SP-B,SP-C,TTF-1 and PLAGL-2 proteins were distributed in the cytoplasm in granular form.The average value of absorbance of SP-B,SP-C,TTF-1 and PLAGL-2 proteins in GDM group was 1.15±0.12,1.23±0.06,0.87±0.21 and 1.21 ±0.18 respectively;and that in control group was 1.22±0.05,1.31 ±0.14,1.12±0.09 and 1.33 ±0.07 respectively.The value in GDM group was lower than that in control group (t=2.40,2.35,4.89,and 2.77 respectively,all P ＜ 0.01).The expression level of SP-B,SP-C,TTF-1 and PLAGL-2 proteins in GDM group was 0.57± 0.09,0.45±0.03,1.50±0.04 and 1.11 ±0.04 respectively;and that in control group was 0.81 ±0.03,0.66±0.04,1.69±0.05 and 1.46±0.07 respectively.The value in GDM group was lower than that in control group (t=1 1.77,11.09,8.80 and 13.37,respectively,all P ＜ 0.01).The mRNA level of SP-B,SP-C,TTF-1 and PLAGL-2 in GDM group was 0.60±0.04,0.79±0.04,0.81 ±0.03 and 0.79±0.05 respectively;and that in control group was 1.06±0.19,1.03±0.24,1.03±0.18 and 1.02±0.19 respectively.The value in GDM group was lower than that in control group (t=6.80,2.98,3.54 and 3.54 respectively,all P ＜ 0.01).Conclusions The protein expression level of SP-B and SP-C in fetal lungs of GDM rats decreases obviously,possibly because of the down-regulation of the gene expression of TTF-1 and/or PLAGL-2.The pathological changes in fetal lungs of GDM rats might be associated with the descending level of SP-B and SP-C protein.