Three-dimensional architecture of elastic tissue in athero-arteriosclerotic lesions of the rat aorta.

The overall three-dimensional architecture of elastic tissue in athero-arteriosclerotic lesions of the ascending aorta of the rat was studied, using scanning electron microscopy (SEM), after hot-formic acid extraction followed by a freeze-drying method. The lesions were induced by feeding the rats a diet containing 2% cholesterol for 6 weeks and administering massive doses of vitamin D2 for the first 4 days. SEM revealed the synthesis of elastins mainly in the intima and the degradation in the internal elastic lamina (IEL) and medial concentric elastic lamellae. Intimal elastic elements involved in atherosclerotic lesions were composed of an intricately tangled network of fibrous elastins or a row of elastic laminae that surrounded many rectangular compartments, which were separated by fenestrated septum-like elastins and were assumed to be the sites of smooth-muscle-cell proliferation. These observations indicated remodelling of the elastic laminae in the intima. Degradation in the IEL and media was attributed to either vitamin D2 intoxication, which was characterized by the formation of a large degraded portion, or an enhanced elastolytic process. These alterations of elastic elements probably reflect the exact frame of the modes of migration of aortic smooth muscle cells in the development of athero-arteriosclerotic lesions, thereby indicating the role of smooth muscle cells in the progress of atherosclerosis.