ObjectiveTo investigate the effect of different dosage recombinant human erythropoietin(rhEPO),an angiogenesis-like factor,on pulmonary angiogenesis exposed to hyperoxia in newborn rats.MethodsSixty Sprague-Dawley newborn rats were randomly divided into four groups:air group (room air exposure,n =15 ),hyperoxia group ( exposed to 95％ oxygen,n =15 ),hyperoxia + large dosage rhEPO group (received rhEPO 5000 U/kg,intraperitoneally on 1 hour before and 3 days after exposed to hyperoxia,n =15) and hyperoxia + small dosage rhEPO group (received rhEPO 800U/kg,the same time points,n =15 ).The isodose of saline were given intraperitoneally on the same time points in the air group and the hyperoxia group.After 6 d of exposure,the survival rate was compared,CD31 and vascular endothelial growth factor (VEGF) were measured by immunohistochemistry to assess hyperoxia-induced changes in lung morphology.ResultsAfter 6d of exposure,hyperoxia + large dosage rhEPO group prolonged the survival rate in comparison with the hyperoxia group [ 86.7 ％ ( 13/15 ) vs 60.0 ％ ( 9/15 ) ].The expression of lung CD31 [ ( 38.69 ±1.69)％ vs (33.57±4.12)％,P＜0.05] and VEGF (124.4296±7.2823 vs 114.2059 ±-8.345 7,P＜0.05) in newborn rats treated with large dosage of rhEPO was significantly higher than those in hyperoxia group.While there was no significant difference of CD31 [ ( 36.34 ± 1.89 ) ％ ] and VEGF( 115.429 6 ± 6.719 9) in small dosage rhEPO group compared with the hyperoxia group (P＞0.05 ).ConclusionInstead of treatment with small dosage rhEPO (800 U/kg),large dosage rhEPO (5000 U/kg) may have important protective effects on pulmonary angiogenesis in hyperoxia-induced lung injury of newborn rats.