Influence of irradiated conditioned medium (IR-CM) and VEGF on the proliferation of U251 glioma cell. U251 GBM glioma cells were incubated for 22 h with conditioned medium or VEGF165 (25 ng/mL) contained medium. Evaluation of cells in mitotic phase was performed using flow cytometry. Samples were fixed, stained with propidium iodide, and analyzed using flow cytometry. Mitotic cells were distinguished from G2 cells, and the mitotic index was determined according to the expression of phosphorylated histone H3 as detected in the 4 N DNA content population by the flow cytometric method of Xu et al. . The data represent the mean of three independent experiments; bars, ± SD.