Regression of atherosclerosis in normotensive and hypertensive rabbits. A quantitative analysis of cholesterol-induced aortic and coronary lesions with an image-processing system.

In the present study we attempted to quantitate the sequential changes occurring in cholesterol-induced aortic and coronary lesions in normotensive and ronovascular hypertensive rabbits, which were placed on a 0.5% cholesterol atherogenic diet for 16 weeks and observed for up to 104 months after withdrawal of the diet. After measuring the degree of surface involvement, a representative longitudinal section covering the whole length of the aorta was obtained, and histometric quantitative analysis was carried out using an image-processing system. Furthermore, ten continuous step-sections of the left coronary artery bed were prepared from each animal, and the degrees of luminal stenosis were estimated in all arterial segments contained. After withdrawal of the cholesterol diet, foam cell lesions of the aorta and coronary artery were gradually replaced by fibromuscular tissue. The hypertensive animals showed a greater degree of smooth muscle cell proliferation. Formation of atheroma occurred almost invariably after cessation of cholesterol feeding, and it was noted that hypertension aggravated the severity and extent of both aortic and coronary atherosclerosis. Upon histometric analysis, evidence of reduction of aortic lesions and significant reversal of luminal narrowing of the coronary artery were observed in normotensive as well as hypertensive animals. These results suggest that, even in hypertensive animals, substantial regression of both aortic and coronary atherosclerosis can be expected after normalization of hypercholesterolemia.