Role of growth factors in the formation of blood vessels.

The turnover of endothelial cells in the normal human adult male is very low, on the order of years. However, in a number of mainly pathological conditions endothelial cells rapidly proliferate, thereby giving rise to new blood vessels (a process called angiogenesis). Angiogenesis-inducing factors have been purified from normal and tumor tissues. Some of these factors are growth or chemotactic factors for endothelial cells. Others have no effect in vitro and are thought to act via indirect mechanisms. Growth and chemotactic factors are also secreted by endothelial cells themselves and may be involved in the development of the vascular wall. In addition they might play a role in atherosclerosis.