Observations of Early Atherogenesis with Calcification Following Aortic Deendothelialization in Rabbits Maintained on a Normal Diet

The factors initiating atherosclerosis in the rabbit model are largely unknown, especially when the animals are maintained on a normal diet. The authors studied regeneration of rabbit aorticintima after balloon deendothelial ization. Eighteen male rabbits were divided into three groups of 6 and under went removal of the thoraco-abdominal aortic endothelium by standard balloon techniques. Animals were sacrificed after four hours (Group I), three days (Group II), and six weeks (Group III). All specimens were evaluated by light (LM) and electron microscopy. Group I showed a gross mural thrombus by LM and complete deendothelialization with a complete layer of platelet deposition. Group II showed disappearance of platelets and reduction in the size of the thrombus. Early myofibroblast (MF) proliferation was seen. Group III showed a well-formed plaque and several layers of MF partially covered with endothe lium. The media was calcified, and there were no foam cells present as are commonly seen in hypercholesterolemic animals. Conclusions: (1) Maintenance of the endothelium is important in preventing atherogenesis. (2) Plaque forma tion occurs early following intimal disruption despite normal calcium metabo lism and a cholesterol-poor diet. (3) Complete endothelial recovery may be in hibited by early plaque formation thus creating a surface conducive to further atherogenesis. This would suggest the possibility of modulating the neointima by the administration of antithromboxane compounds or prostacyclin ana logues.