Abstract
The ultrastructural changes and permeability of endothelial cells which are located in both lesionresistant and susceptible regions on the flow dividers at bifurcations of the brachiocephalic trunk and left subclavian artery were studied. Sixty-four and 22 male white adult rabbits were fed for up to 2 weeks with a cholesterol diet and a stock diet, respectively. For the permeability studies, horseradish peroxidase (HRP), ferritin and immunoglobulins against HRP produced autologously were used as tracers. Sudan IV stain revealed that the apex and leading edge of the flow dividers were spared from lipid deposition in the second week of the cholesterol diet. The deposition could be observed in a band-like fashion in regions 460μm downstream from the apex of both flow dividers. Apo E and B deposition was also immunohistochemically detected in the sudanophilic areas. Foam cells appeared successively following lipid deposition. Endothelial cells at the leading edge, lesion-resistant area, were elongated along the flow direction and had more microfilament bundles and fewer mitochondria in their cytoplasms, as well as thick basement membranes. In the shoulders, a lesion-prone area, they had more vacuoles, RER, Golgi apparatuses and mitochondria, but had fewer stress fibers in their cytoplasms. The permeability of endothelial cells to HRP and ferritin was enhanced in the shoulders of even normal rabbits. Permeability to immunoglobulins increased only in the shoulders of hyperlipidemic rabbits. The glycocalyx on the endothelium of normal rabbits was thicker at the leading edge than in the shoulders. Hyperlipemia decreased the thickness of glycocalyx at both the leading edge and in the shoulders, although this was more obvious in the shoulders.
In conclusion, lesion-prone areas in rabbits are located in areas exposed to low-shear stress just as in humans. These areas showed a higher permeability even in normal rabbits.
