Age-related changes in aortic intima of rats.

The aortic intima of young and old Wistar rats was studied by light and electron microscopy. The endothelial cells of young rats are flat and regular and lie adjacent to the internal elastic lamina (IEL). Endothelial cells of old rats have irregular shapes and sizes and bulge into the lumen. Long protrusions connect these cells to the IEL through a layer of granular and fibrillar material that separates the IEL from the endothelium. This material is PAS and Alcian blue positive and increases with age. There are twice as many pinocytic vesicles on the luminal front of endothelial cells of old rats as compared to the tissue front. Endothelial cells of young rats have similar numbers of vesicles on the two fronts. No significant difference was found between the charge density of the luninal plasmalemma of young and old rats; however, significantly less sialyl groups were found on endothelial cells of old rats. A marked difference in the labeling pattern of the IEL by cationized ferritin (CF) was observed between young and old rats.