Influence of shear stress on endothelial cell shapes and junction complexes at flow dividers of aortic bifurcations in cholesterol-fed rabbits.

We studied the effects of hemodynamic forces on endothelial cell shape and junction complexes in sudanophilic and non-sudanophilic regions at flow dividers of aortic bifurcations in normolipidemic and hyperlipidemic rabbits by scanning electron microscopy (SEM) and the freeze fracture method. Flow profiles and shear stresses were obtained by tracing the paths of particles in a transparent vessel in steady flow. No apparent differences between normolipidemic and hyperlipidemic rabbits were observed by SEM. The tip of the apex of flow dividers, a point of stagnated flow, and the leading edge, which was exposed to laminar, high shear stress, were non-sudanophilic, and were covered by, respectively, round and long fusiform endothelial cells. The tight junctions were continuous and gap junctions had a regular shape. The hip of the flow dividers of branchings, a relatively low shear stress region, was sudanophilic and was covered by ellipsoidal cells with discontinuous tight junctions and irregularly shaped gap junctions. Our results suggest that endothelial cells exposed to relatively low wall shear stress, but not to high shear stress, may be functionally activated, leading to an increased intercellular permeability, which may make these regions vulnerable to atherosclerosis.