Regional variation in rat aortic endothelial surface morphology: relationship to regional aortic permeability.

The regional variation of rat aortic lumenal surface topography has been examined by employing techniques of scanning electron microscopy. This study was undertaken in an attempt to gain additional insight into the current controversy regarding endothelial folds and cross bridges and their possible role with respect to regulation of vessel transmural permeability. Within the ascending aorta, aortic arch, and upper third of the thoracic aorta distinct, prominent endothelial folds connected by interlinking cross bridges were easily identifiable. The middle third of the thoracic aorta contained less prominent endothelial folds; photomicrographs from these regions consistently failed to reveal the presence of any interfold cross bridges. In the lower third of the thoracic aorta, endothelial folds were notably lacking. These differences in regional aortic surface topography have been discussed in light of known regional differences in aortic wall permeability and with respect to regional differences in apearance of endothelial silver-staining lines.