Capillary growth from reversed rat aortic segments cultured in collagen gel.

The process of angiogenesis from aortic segments turned inside out and embedded in collagen gel was studied. Two to three days after inoculation, fibroblastic cells migrated from both ends of the segments. Later, capillary sprouts also appeared from both ends of the segments but not from the outer surface, even though there was a covering of endothelial cells. If the outer surface was injured, capillaries sometimes appeared at the damaged site. This may suggest that endothelial cells have more affinity for basement membrane than collagen gel and that they migrate only from an injured site. Immunohistochemical staining demonstrated factor VIII-related antigen in the capillary structures but not in the fibroblastic cells. Electron microscopically, capillary lumina were lined with several endothelial cells, and fibroblastic cells had the characteristics of smooth muscle cells. Since these fibroblastic cells have been known to appear under angiogenetic conditions in vivo, they may play an important role in angiogenesis, and the present culture technique may be a useful model for studying this process.