Angiogenesis: an update.

Angiogenesis is the neovascularization or formation of new blood vessels from the established microcirculation. It is particularly important and indispensable in a large number of normal and pathological processes during pre- and post-natal life, including neoplasia, inflammation, wound repair and collaterization in response to ischemic stimuli. The current interest in the role of neovascularization in the transition from hyperplasia to neoplasia, as well as in the tumour growth and metastasis, has brought about a large number of studies on angiogenesis. The complex processes of neovascularization, quiescent in the adult organism, may occur rapidly in several circumstances, with the implication of the following events: a) endothelial cell (EC) and pericyte activation; b) basal lamina degradation; c) migration and proliferation of EC and pericytes; d) formation of a new capillary vessel lumen; e) appearance of pericytes around the new capillaries; f) development of a new basal lamina; g) capillary loop formation; h) persistence or involution, and differentiation of the new vessels; and i) capillary network formation and, eventually, organization into larger microvessels. The use of numerous "in vivo" and "in vitro" systems has facilitated the assessment of angiogenesis control, in which angiogenic (fibroblast growth factors, vascular endothelial growth factor, platelet endothelial growth factor, E series prostaglandin, angiogenin, monobutyrin) and antiangiogenic (cartilage-derived angiogenic inhibitor, thrombospondin, protamine, platelet factor 4, interferon, angiostatic antibiotics, steroids) substances intervene. Heparin and heparin sulphate also play a key role in these mechanisms. A greater knowledge of angiogenesis control may lead to the development of a potential therapy in angiogenesis-related processes.