OBJECTIVENeonatal 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.

METHODSThe 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.

RESULTSFollowing 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.

CONCLUSIONThe 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.