BACKGROUNDTo investigate the origin of tumor blood vessel and blood supply during pulmonary carcinogenesis, and the relationship between vascular endothelial growth factor (VEGF), its receptor Flk-1 and angiogenesis.

METHODSOne hundred Wistar rats were instilled with 3-methylcholanthrene (MCA) and diethylinitrosamine (DEN) to induce pulmonary squamous cell carcinoma through left lower lobe bronchus. To acquire different pathological phase during the carcinogenesis, rats were killed in 15, 35, 55, 65, 75 days after instillation. Yellow and green silastics were respectively injected into the bronchial and pulmonary arteries of 30 rats in 55, 65, 75 days after instillation. Intertumor microvessel density (MVD) was marked by anti-von Willebrand factor monoantibody. VEGF and Flk-1 expression were examined by immunohistochemistry.

RESULTSIn the tumor area the tumor blood vessels were yellow and connected with distorted bronchial artery and very few green incomplete branches of pulmonary artery were seen. Silastic particles could be seen in the disordered tumor blood vessels by microscope after bronchial artery perfusion. There was no silastic particles in the carcinoma interstitial blood vessels after pulmonary artery perfusion. MVD count significantly increased in carcinoma in situ (39.50±12.60) and infiltrative carcinoma (61.05±19.92) as compared to atypical hyperplasia (8.92±3.80)(both P < 0.01), and the increased vessels originated from bronchial artery, but not pulmonary artery. The expression of VEGF and Flk-1 increased during pulmonary carcinogenesis. The positive coefficients of VEGF and FLK-1 expressions became higher and higher from epithelial proliferation to squamous metaplasia, to atypical hyperplasia, to carcinoma in situ and finally to infiltrative carcinoma. There was significant correlation between MVD and VEGF expression (r=0.979 8, P < 0.005), as well as between MVD and Flk-1 expression (r=0.907 8, P < 0.05).

CONCLUSIONSAngiogenesis is the important phenomenon of the rat pulmonary carcinogenesis and the newly formed blood vessels in tumor connect with the branches of bronchial artery, but not pulmonary artery. This confirms that the blood supply of pulmonary carcinoma is from bronchial artery, not from pulmonary artery. VEGF and Flk-1 are closely related to angiogenesis of tumor.