Age-induced changes in the aortas of rats.

In order to elucidate changes due to age in blood vessels, the aortic walls of Wistar rats ranging in age from 35 to 45 months were examined with an electron microscope. The remarkable changes of the walls were found mainly in the media: smooth muscle cell necrosis, increase of ground substances, as well as collagen fibrils, and calcification in some of the necrotic muscle cells. Branched smooth muscle cells were often found in the media. Elastic networks in the media, however, were hardly ever destroyed. The spider-web fashion in the peripheral cytoplasm of the smooth muscle cells was observed in all animals. Diffuse or localized slight intimal thickening could be seen in the subendothelial spaces, but aortic atherosclerosis was not present in the intima. No remarkable changes were seen in the adventitia.