Experimental Atherosclerosis: Surface Ultrastructural Studies in the Rabbit Aorta

Numerous techniques have been employed in the study of experimental atherosclerosis. This study employs critical point drying, cryofracture and transmission and and scanning electron microscopic studies of experimental atherosclerosis in New Zealand white rabbits. Rabbits were maintained on a diet containing 1% cholesterol and 5% Wesson oil and had serum cholesterol levels of 1800 to 2100 mg/dl. Animals were sacrificed at 100 days, 181 days, 217 days, 225 days and 246 days after starting the atherogenic diet. Animals were fixed by perfusion, using Tyrode’s solution followed by Trump’s fixative. Most severe lesions were in the ascending aorta. Least severe lesions were in the common iliac arteries. Very early lesions had widened intimal spaces containing free lipid and smooth muscle cells containing lipid vacuoles. These lesions had distinct borders or were irregular and diffuse. More severe lesions had micro-ulcers at irregular borders. Endothelium over the surface of such lesions was variable and usually intact. An occasional cell with microvilli was observed. By cryofracture cells contained lipid vacuoles with multiple intercommunications. In later lesions cholesterol clefts were also seen. Lipid vacuoles were also observed 1n endothelial cells and in smooth muscle cells of the superficial media. It seems reasonable to conclude that lipid is transported into the subendothelial intimal space and there taken up by smooth muscle cells.