© 1996 Journals of Reproduction and Fertility

Angiogenesis refers to the formation of new blood vessels, or neovascularization, and is essential for normal tissue growth and development (Folkman and Klagsbrun, 1987; Klagsbrun and D’Amore, 1991). The angiogenic process begins with capil-lary proliferation and culminates in formation of a new micro-circulatory bed composed of arterioles, capillaries and venules. The initial component of angiogenesis, capillary proliferation, consists of at least three processes: (1) fragmentation of the basement membrane of the existing vessel, (2) migration of endothelial cells (the primary cell type constituting capillaries) from the existing vessel toward the angiogenic stimulus and (3) proliferation of endothelial cells (Folkman and Klagsbrun, 1987; Klagsbrun and D’Amore, 1991). Neovascularization is completed by formation of capillary lumina and differentiation of the newly formed capillaries into arterioles and venules