The appearance of the aortic wall of rabbits fed a
lanolin containing diet was examined by scanning (SEM) and transmission electron microscopy (TEM) in order to clarify the mechanism of removal of
lipids deposited in the aorta. SEM study showed that circulating leukocytes penetrated into the arterial wall in the early phase of the experimental
atherosclerosis. In some specimens, spherical bodies with a diameter of 10-30 mu were observed along the cleavage of the marginal folds between the endothelial cells. TEM demonstrated that these bodies contained many
lipid particles, and numerous active microvilli were seen on the body surface. In the deeper subendothelial space, villi of each body interdigitated. From these results, it is postulated that the circulating leukocytes penetrate under the endothelium and take up the deposited
lipids. Then, they return to the blood stream, containing
lipid rich particles. The deposited
lipids in the atherosclerotic lesion would be removed by this process. We named this phenomenon as "exo-tissuesis with
lipid containers". While
lipids are believed to be removed from the atherosclerotic lesion by
HDL, lecithin cholesterol acyltransferase and others at the molecular level, we suggest that
lipid containers play important roles in the regression and prevention of
atherosclerosis on a major scale-cellular and tissue level.