Regression of arteriosclerotic lesions in rhesus monkey aortas after regression diet. Scanning and transmission electron microscope observations of the endothelium.

Scanning and transmission microscopy were used to study aortic intima atherosclerotic lesions in Rhesus monkeys during both progression and regression phases. Scanning micrographs of severely atherosclerotic lesions showed areas of disjunctive endothelium and discontinuous basement membranes, frequently accompanied by red blood cells and other circulating elements adhering to the surface. Transmission micrographs also showed occasional areas of endothelial cell damage and loss with lipid-laden smooth muscle cells and foam cells beneath. Regressed lesions (affected by low-fat, low-cholesterol diet with or without cholestyramine) showed endothelial changes suggestive of reparative processes. Scanning micrographs showed flattened residual lesions with continous endothelial lining, while transmission microscopy disclosed interdigitated intercellular tight junctions and frequently reduplicated basement membranes.