Degradation of basement membrane components by vascular endothelial cells: role in neovascularization.

A retina-derived substance (or substances) has been identified that stimulates vascular endothelial cells to degrade three structural components of basement membrane: type IV collagen, fibronectin and laminin. In basement membrane surrounding existing blood vessels, endothelial cells stimulated in this way can presumably migrate through the resulting gaps and form new vascular sprouts. These events may therefore represent the earliest steps in the formation of new blood vessels.