FORMATION OF NEW CAPILLARY-LIKE TUBES IN A 3-DIMENSIONAL IN-VITRO MODEL (AORTA COLLAGEN GEL)

Direct sprouting (angiogenesis) does not occur during the formation of capillary-like tubes in an aortal collagen gel in the in vitro model. However, emigration of cells which stretch, arrange themselves side b y side, form contacts (unspecific, tight and gap junctions), develop a lumen and show differentiation of endothelial cells (including the fo rmation of a lamina densa and the appearance of pericytes) have been o bserved, i.e. vasculogenesis occurs. The origin of long, stretched cel ls is not known with certainty. They possibly represent smooth muscle cells. In addition, other cell types have been found, such as fibrocyt e-like and fibroblast-like cells, elastoblasts, fat cells, monocytes a nd macrophages. All these cells are able to produce factors that promo te the formation of new capillaries. Hence, a knowledge of these cells appears to be important for the analysis of in vitro systems. Moreove r, the occurrence of these cell types must be considered when assessin g possible effects.