Atherosclerosis in Rabbit Vein Grafts

Human coronary saphenous vein bypass grafts develop atherosclerosis more readily than do grafts made of internal mammary artery. The reasons for this Increased susceptibility, particularly In the presence of hyperlipidemla, are not known. In this study in rabbits, we Investigated the possibility that the Increased susceptibility might be attributed to Increased smooth muscle proliferation and foam cell accumulation In vein grafts compared to native artery. Hypercholesterolemlc and control rabbits underwent placement of jugular vein grafts In the carotid artery. Dietary cholesterol content was adjusted to maintain serum cholesterol levels of 200 to 600 mg/dl in the fat-fed rabbits. The vein graft Intlmal thickness In hypercholesterolemlc rabbits was greater than in normollpemlc rabbits at 3 and 6 months after Implant. The Increased thickness in the hypercholesterolemlc group was largely accounted for by an accumulation of llpld-laden macrophages. Medial thicknesses Increased during the first month, remained constant at later times, and were similar in control and hypercholesterolemlc animals. In both groups, endothellal and smooth muscle cell proliferation (thymldlne labeling) increased Immediately after graft Implantation and declined at 3 and 6 months. No Incremental mltogenic stimulus could be attributed to the hypercholesterolemia. In Immunohlstochemlcal preparations, the large foam cells were noted to be macrophages, and the Intlmal proliferating cells, to be smooth muscle. Proximal and distal carotid artery segments adjacent to the vein grafts In hypercholesterolemlc rabbits had virtually no accumulation of llpld-laden macrophages. These results suggest that the endothellal and smooth muscle cell response In vein grafts adapting to the arterial circulation Is not altered by hyperlipidemla, but that the wall becomes thick because of an accumulation of llpid-laden macrophages.