Three patterns of distribution characterize the organization of endothelial microfilaments at aortic flow dividers.

Since actin microfilaments are essential in the maintenance of endothelial integrity and in the repair of injured endothelium, we have carried out a detailed study of the distribution of microfilaments in the immediate vicinity of aortic branches. Branches are of major interest because there is a predilection for atherosclerotic lesions near branch ostia. We made an extensive, systematic examination of branches of the aorta and iliac arteries using in situ staining of perfusion-fixed arteries. Microfilaments were localized using rhodamine phalloidin. Three patterns of staining were observed. Some endothelial cells showed prominent central stress fibers. Others had few central stress fibers but prominent peripheral fibers. Still others showed an intermediate pattern with some central and some peripheral fibers present. At small branch sites, the lip of the divider was more blunt, and there were more cells with peripheral actin. At large branches, cells with peripheral actin were confined mainly to the lip, while there were many more cells with prominent central fibers. We also found that major differences can occur over very small distances, so adjacent cells may have strikingly different patterns of microfilament distribution. These patterns appear to reflect the geometry of the flow divider and local variations in hemodynamic shear stress. The differences in microfilament distribution may reflect differences in endothelial functions which are essential in maintaining endothelial integrity.