Mosaicism in female hybrid hares heterozygous for glucose-6-phosphate dehydrogenase. IV. Aortic atherosclerosis in hybrid hares fed alternating cholesterol-supplemented and nonsupplemented diets.

Hybrid hares provide a model for induction of aortic atherosclerosis. The basic dietary regimen consisted of cholesterol-supplemented and nonsupplemented commercial pellets alternating at 1-week intervals for up to 18 months. Controls were fed nonsupplemented pellets. Control aorta features included branch cushions, intimal thickenings unrelated to branches, and several longitudinal layers of smooth muscle in the outer media. Branch cushions extended longitudinally in the main vessel, and had multidirectional, streamlike bundles of smooth muscle in the intima and media. Intimal thickenings unrelated to branches occurred as longitudinal patches, most frequently in the ventral quadrant. The adjacent media had a regular array of cells. Raised lesions concentrated at branch orifices and in the ventral quadrant. Lesions involved up to 80% of the thoracic and 40% of the abdominal aorta by 5 months. Predominant lesions consisted of superficial fibromuscular tissue and deeper foam cells and stainable lipids. Some of these lesions were atheromata with fibrous cap. Fibromuscular plaques, 120 to 150 micron thick, had a few superficial foam cells and hydropic degeneration. Foam-cell lesions were also observed. Data obtained suggest the importance of branch cushions and intimal thickenings unrelated to branches, and of the periods on nonsupplemented pellets.