Hydrodynamic injury of the endothelium in acute aortic stenosis.

The acute effects of increased shear stress on the endothelium were studied by reducing the lumen of the rat aorta to 20-25% of normal by means of metal clips. Intimal damage in the stenotic area was assessed by light microscopy after perfusion with AgNo3 and study of the endothelium en face. Most of the endothelium was lost within 3 minutes; the extent of the damage was not increased after 1 hour. Electron-microscopic examination showed that some endothelial cells became permeable to tracers (thorium dioxide and horseradish peroxidase); platelets adhered to the exposed internal elastic membrane. Focal endothelial changes were represented by myelin figures of various kinds arising from the luminal surface and by "cellular ulcers," superficial erosions of the endothelial cells accompanied by localized cytoplasmic changes. These "ulcers" occurred more frequently over the nucleus and near junctions; they have not been described in other forms of arterial injury.