Regression of atherosclerosis and centrally depressed lesions in rabbit aortas

Atherosclerotic plaque with central depression (depressed lesion) has been hypothesized to be a morphological feature of atherosclerosis regression. We tested this hypothesis in New Zealand white rabbits. After the animals were fed a diet containing 1% cholesterol for three months, they were changed to a normal diet for 6 to 9 months. Several aortas had centrally depressed lesions similar to those found in elderly people, and the animals had low serum cholesterol levels. Immunohistochemical study showed that the depressed lesions contained more smooth muscle cells and collagen type IV, and fewer macrophage-derived foam cells than did common atherosclerotic elevated lesions found in rabbits. We know of no other report of depressed lesions in rabbits with atherosclerosis. Thus we believe that the centrally depressed lesion is a histological characteristic of regression of atherosclerosis.