OBJECTIVETo study the effects of prolonged 85% oxygen exposure on lung vascular development and the expression of angiopoietin-1 (Ang-1) in the neonatal rat lungs.

METHODSNinety-six Sprague-Dawley rat pups were randomly exposed to air (control group) and 85% oxygen (experimental group) 6 hrs after birth. The rats were sacrificed 3, 7 and 14 days after exposure and their lungs were sampled. The lung sections were stained with hematoxylin and eosin for histological evaluation and analysis of vessel volume density. Expressions of angiopoietin-1 (Ang-1) in lung tissue were measured by immunohistochemistry. Expression of Ang-1 protein and mRNA was detected by Western Blot and Real time-PCR.

RESULTSAfter being exposed to 85% oxygen for 14 days, lung tissues had pathological changes as "new" bronchopulmonary dysplasia (BPD). The RAC on day 7 and day 14 in experimental group decreased significantly as compared with the control group [(10.55 ± 0.13) vs. (11.74 ± 0.19), (12.47 ± 0.05) vs. (15.03 ± 0.16), P < 0.05]. The X-ray showed that the diameter of lung vessel was much smaller and the vessels had less branches in experimental group compared with the control group on day 14. The vessel volume density on day 14 in experimental group decreased significantly as compared with the control group [(3.55 ± 0.09) vs. (6.03 ± 0.16), P < 0.05]. Immunohistochemistry and Western blotting showed that the expressions of Ang-1 protein on day 7 and day 14 in the experimental group decreased significantly as compared with the control group [(4.27 ± 0.34) vs. (3.10 ± 0.29), P < 0.05, (5.65 ± 0.49) vs. (3.21 ± 0.28), P < 0.01], [(0.88 ± 0.31) vs. (0.41 ± 0.12), P < 0.05, (0.90 ± 0.29) vs. (0.21 ± 0.06), P < 0.01]. The expressions of Ang-1 mRNA on day 7 and day 14 in the experimental group also decreased significantly as compared with the control group [(0.85 ± 0.14) vs. (0.44 ± 0.21), P < 0.05, (0.87 ± 0.24) vs. (0.24 ± 0.05), P < 0.01].

CONCLUSIONSProlonged exposure of high concentration of oxygen may cause impairment of lung vascular development by inhibiting expression of Ang-1 in neonatal rats, which is likely to contribute to pathogenesis of BPD.