tokens: To elucidate the role of estrogen in the regulation of tumor angiogenesis in the pituitary of female rats , the density of blood vessels was analysed using factor VIII related antigen ( FVIIIRAg ) immunohistochemistry and the expression of vascular endothelial growth factor / vascular permeability factor ( VEGF / VPF ) was examined by Western blot and immunohistochemical analysis .