OBJECTIVETo study the effects of prolonged 75% oxygen exposure on the expression of vascular endothelial growth factor (VEGF) and its receptors (VEGFR1 and VEGFR2) in the neonatal rat lungs and to elucidate the effects of prolonged exposure of high concentration of oxygen on lung vascular development and its relationship with bronchopulmonary dysplasia (BPD).

METHODSForty eight Sprague-Dawley rat pups were randomly exposed to air (control group) and 75% oxygen (experimental group) 12 hrs after birth. The rats were sacrificed 7, 14 and 21 days after exposure and their lungs were sampled. The lung sections were stained with hematoxylin and eosin for histological evaluation. Expression of VEGF, VEGFR1 and VEGFR2 protein and mRNA was detected by immunohistochemistry and RT-PCR.

RESULTSAfter being exposed to 75% oxygen for 21 days, lung tissues had pathological changes as 'new' BPD. Expressions of VEGF protein (10.9 + or - 2.7 vs 30.8 + or - 6.4), VEGFR1 protein (5.4 + or - 1.4 vs 15.6 + or - 3.4) and VEGFR2 protein (11.3 + or - 2.6 vs 21.7 + or - 4.5) on day 21 in the experimental group decreased significantly as compared with the control group (p<0.05). The expression of VEGF mRNA (1.6 vs 3.3), VEGFR1 mRNA (0.4 vs 6.6) and VEGFR2 mRNA (0.5 vs 4.9) on day 21 in the experimental group also decreased significantly as compared with the control group (p<0.05).

CONCLUSIONSProlonged exposure of high concentration of oxygen may cause BPD possibly by inhibiting lung vascular development in neonatal rats.