The formation of endothelial webs and channels in plasma clot culture.

Rings of rat aorta cultured in plasma clots gave rise to microvascular networks. Scanning electron microscopy revealed that, in most cultures, the newly formed microvessels communicated with an endothelial-lined chamber which had developed around the aorta. The endothelial cells lining the wall of this chamber were elongated and frequently overlapped each other forming unicellular or multicellular bridges. The endothelium also produced solid bands and webs which spanned wide regions of the periaortic chamber and of the aortic lumen. Solid endothelial ropelike structures overran the openings of the newly formed vascular channels and connected the outer wall of the chamber with the aortic ring. Webs were composed of branching cords of spiraling endothelial cells with or without collagenized cores. Webs and bands formed as a result of the extensive surface remodeling of the fibrin clot by developing endothelial channels. These structures are reminiscent of the intimal bands and webs which develop in human blood vessels as a late sequela of the organization of thromboemboli.