Aortic intimal changes in aging swine.

Aortic intimal lesions in aging swine contained smooth muscle, monocyte-like and unclassifiable cells. The most frequent cellular constituent was the smooth muscle cell that had slightly different features than those in the media. Monocyte-like and unclassified cells appeared largely in the innermost layer of the intima; both types of cells were ultrastructurally similar in appearance except the former had heterophagic vacuoles and overall resemblance to circulating monocytes in shape and size. These cells seemed to preexist in aortic lesions of untreated, aging swine. The intima-media strips of the grossly normal thoracic aortas in 3 1/2 year old swine showed significantly higher contents of cholesterol, triglycerides, phospholipids and total lipids than those of a 6 month old swine. Three to four month old cultured aortic cells accumulated extracellular components, such as fibriles, electron dense substances and cellular debris, which appeared similar to the extracellular matrix of aortic plaques in aged swine.