In vivo modulation of endothelial F-actin microfilaments by experimental alterations in shear stress.

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Abstract
F-actin microfilament reorganization in response to alterations in shear stress has not been experimentally tested in vivo. In the current study, we analyzed changes in F-actin distribution in endothelial cells around the site of a coarctation performed in the midabdominal aorta of rabbits. The coarctation caused a 60% decrease in luminal diameter and produced three distinct zones: 1) a high shear region immediately upstream of the coarct (Zone I); 2) a region of low, fluctuating shear immediately downstream of the coarct (Zone II); and 3) an annular vortex characterized by high shear extending 0.5 to 3 mm downstream of the coarct (Zone III). Endothelial cells of control abdominal aortas were ellipsoid in shape and aligned in the direction of blood flow. They displayed a prominent circumferential band of microfilaments and short, thin stress fibers. Near coarctations, cells of Zone I were much more elongate, and stress fibers were markedly thicker and longer than in control abdominal aortas. In Zone II, c...