Recent studies have suggested that immunological alterations induced by vasectomies may cause an exacerbation of the atherogenic process. The exact mechanism whereby this potentiation occurs is unknown. The experiments presented in this proposal are designed to gain additional information concerning the biochemical changes which occur in arterial tissues during the development and regression of immunologically stimulated atherogenesis. Rabbits which have induced serum sickness and are fed a moderately elevated cholesterol diet will be utilized. Time dependent studies following the induction of serum sickness will measure changes in aortic permeability, cholesterol content, protein content and protein synthetic rates. Changes in serum lipoproteins will also be monitored. These parameters will be measured in the presence and absence of a continuing elevated cholesterol diet. The biochemical changes in all these studies will be coordinated with histological alterations of the aortic wall. The studies as proposed will provide needed information concerning the consequences of immunologically induced injury of the aortic wall. The hypothesis to be tested is that in immunologically stimulated atherogenesis, elevation of aortic permeability and elevation of aortic protein metabolism are both prerequisites for accumulation and retention of aortic cholesterol.