Chorioamnionitis is associated with preterm delivery and bronchopulmonary dysplasia (BPD), characterized by impaired alveolar and pulmonary vascular development and vascular dysfunction. To study the vascular effects in a model of chorioamnionitis, preterm lambs were exposed to 20 mg of intra-amniotic endotoxin or saline for 1, 2, 4, or 7 days and delivered at 122 days gestational age (term = 150 days). This intra-amniotic endotoxin dose was previously shown to induce lung maturation. The effect of intra-amniotic endotoxin on expression of endothelial proteins was evaluated. Muscularization of the media and collagen deposition in adventitia of small pulmonary arteries was used to assess vascular remodeling. Compared with controls, bronchoalveolar lavage fluid protein content was increased 2 days after intra-amniotic endotoxin exposure. Vascular endothelial growth factor (VEGF) 165 isoform mRNA decreased 2-4 days after intra-amniotic endotoxin. VEGF, VEGF receptor-2, endothelial nitric oxide synthase (eNOS), platelet endothelial cell adhesion molecule-1, and Tie-2 protein expression in the lung coordinately decreased 1-7 days after intra-amniotic endotoxin. Intra-amniotic endotoxin appeared to selectively decrease eNOS expression in small pulmonary vessels compared with large vessels. Medial smooth muscle hypertrophy and increased adventitial fibrosis were observed 4 and 7 days after intra-amniotic endotoxin. These results demonstrate that, in the preterm lamb lung, antenatal inflammation inhibits endothelial cell protein expression followed by vascular remodeling changes in small pulmonary arteries. Exposure to antenatal inflammation may cause vascular remodeling and contribute to the development of BPD.