Lesions in the rabbit aorta that occur spontaneously and contain no lipid consist of intimal mesenchymal proliferation and of medial sclerosis. Although the relationship of diet-induced atheroma to the intimal mesenchymal alterations is still not clear, our experiments have established that (a) the morphologic characteristics of diet-induced atheroma and of the spontaneous medial lesions are dissimilar at all stages of their development, and (b) the presence of spontaneous medial lesions

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... influences the development of atheroma. This influence is related to (a) an increased tendency for atheroma formation at the raised proximal and lateral borders of nodular medial lesions projecting from the luminal surface, (b) the absence of atheroma formation at sites of medial calcification, and (c) a propensity for lipid deposition in areas of acid mueopolysaccharide accumulation within spontaneous medial lesions. Results GROSS APPEARANCE Focal yellow plaques, which stained red with oil red O, were present on the aortic