OBJECTIVETo explore the relationship between the injury of vascular endothelial cells and formation of lung fibrosis by bleomycin (BLM) in rats.

METHODSThe rats of experimental groups were treated with bleomycin intratracheally to induce pulmonary fibrosis. The expression of vascular endothelial growth factor (VEGF) in pulmonary tissues were analyzed qualitatively and quantitatively by immunohistochemistry and image analysis system.

RESULTS(1) HISTOLOGY: Edema in rat alveoli and alveolar septum, inflammatory cells exudation, degeneration and necrosis of type I and type II alveolar epithelial cells (AETI and AETII), ruptured alveolar basement membrane, as well as swollen vascular endothelial cells and karyopyknosis were observed in 3 d and 7 d after treatment with BLM. AETII proliferation, with more fibroblasts in alveolar septum, and new capillary vessel formation in 7, 14 d, as well as thickened alveolar septum, damaged alveolar structure, and obvious pulmonary tissue fibrosis in 28 d after treatment with BLM were observed. (2) Immunohistochemistry: in normal control, VEGF expressed weakly in pulmonary tissue distributing mainly in AETII, bronchial epithelial cells, alveolar macrophages and leydig's cells. While in bleomycin treated groups, the expression of VEGF increased markedly. The expression in AETII, and pulmonary macrophage were significantly higher than that in control in 3 d to 28 d (P < 0.05, P < 0.01). The rat leydig's cells also had higher expression of VEGF in 7, 14, 28 d (P < 0.05, P < 0.01).

CONCLUSIONThe high expression of VEGF is related to vascular endothelial cells injury which may be one of important factors in the formation of bleomycin-induced pulmonary fibrosis.