弾性線維の超微構造, 新生, 崩壊

Abstract

Elastin substructure, sequential changes of elastolysis were studied by electron microscopy using tannic acid stain. Prolonged treatment of rabbit carotid arteries with periodate or osmium tetroxide removed tannic acid-reactive materials from the central amorphous portion of elastic fibers with resultant disclosure of the fibrils approximately 4nm in diameter, which were readily digested by elastase. Based on these findings it was considered that the central amorphous portion consists of a fibrillar network of elastin which is embedded in tannic acid-reactive materials. In the stenotic segments induced by constriction of the common carotid arteries of rabbits, elastolysis proceeded through two steps: initially tannic acidreactive materials were removed, and then fibrillar network of elastin dissolved remaining peripheral microfibrils.Light and electron microscopic observations were made on elastolysis and elastogenesis during the developement of experimental atherosclerosis produced in cholesterol-fed rabbits by partially constricting the carotid artery. The internal elastic lamina disrupted within a week after constriction in the same process of elastolysis observed in the stenotic segments. During this time, smooth muscle cells were migrated from the media into the intima, where they proliferated. Subsequently numerous elastic fibers were formed by smooth muscle cells and the disrupted internal elastic lamina was also regenerated. In advanced stages, elastolysis predominated over elastogenesis and elastic fibers deposited in the intima were degraded showing the similar features to those observed in the stenotic segments. Whereas, bundles of microfibrils lacking elastin or associated with only tiny elastin aggregates were seen deposited around the smooth muscle cells. Large amount of lipids deposited particularly in the central portion of the elastic fibers and calcium deposited on microfibrils, suggesting that degraded elastin and overproduced microfibrils may have predilection for the deposition of lipids and calcium.