Failure of regression of atherosclerosis in dogs with moderate cholesterolemia

Controversy exists as to whether regression occurs in atherosclerotic plaques in response to serum cholesterol reduction. In the present study, using sequential observation of canine atherosclerosis, we attempted regression in hypothyroid dogs. Animals with established lesions prior to a regression attempt were placed on a 0.05% cholesterol diet and observed up to 60 months. Weighted average cholesterols ranged from 235 to 587 mg/100 ml during the regression attempt. A control fed for the entire period of the experiment, 75 months, had an average weighted cholesterol of 435 mg/100 ml. We failed to obtain regression of atherosclerotic plaques in spite of reduction of serum cholesterol from high to moderate levels. The lesions in the experimental animals contained less lipid and more collagen and calcium than occurred in the control. Complicated plaques with aneurysm formation, stenosis of the distal aorta, and gangrene of the tail were also noted.