Intimal cell masses in the abdominal aortas of swine fed a low-fat, low-cholesterol diet for up to twelve years of age

Abstract

The normal subendothelial intima of large arteries in man, swine and most other species is a variegated structure from birth onwards. In some regions it contains only a few scattered cells; in others there may be a continuous single layer of cells; and in still others the cells pile up to form what we have called intimal cell masses (ICM). The cells in the normal ICM are mostly smooth muscle cells although there is also a small resident population of monocyte-like cells. We have been studying the ICM in swine with emphasis on the abdominal aorta. We have found that atherosclerotic lesions in the abdominal aorta of swine induced by high-fat high-cholesterol diets begin by a hyperplastic reaction of the smooth muscle cells in the ICM and progress to form large lesions characterized by extensive regions of lipid-rich calcific necrotic debris similar to advanced lesions in man. Because of the putative key role of the ICM in atherogenesis we think that it is important to learn as much as possible about their natural history under conditions as normal as possible. In this report we present data on ICM in the abdominal aortas of 34 male and female Hormel miniature swine maintained on a low-fat low-cholesterol diet for up to 12 years of age. The ICM grow slowly with aging and in the distal portion of the aorta account for an average of 9% in the male and 15% in the female of the total cells in the aortic wall (intima + media). They differ from atherosclerotic lesions induced by hyperlipidemic diets in being generally smaller, containing relatively small amounts of lipid and calcium and in seldom showing necrosis with accumulation of debris.