In experimental BPD in newborn rats alveolar enlargement and loss of lung capillaries are associated with decreased expression of lung VEGF and VEGF receptor-2 (VEGFR2) [44], whereas sildenafil improves alveolarization and angiogenesis [14], and reduces pulmonary fibrin deposition, inflammation and vascular alveolar leakage, resulting in prolonged survival in the present study. This evidence concerns the gene KDR and bronchopulmonary dysplasia.