Abnormal accumulation of elastin-associated microfibrils during elastolysis in the arterial wall.

We examined the correlation between elastolysis and abnormal accumulation of microfibrils in the arteries of rabbits using light and electron microscopic and tissue culture techniques. Partial constriction of the common carotid arteries of rabbits gave rise to gradual atrophy of the media with elastolysis and an unusual accumulation of microfibrils. With advancing experimental atherosclerosis in cholesterol-fed rabbits, the elastofibrotic intima generally became thick and hyalinized and was replaced by bundles of microfibrils lacking elastin or associated with only tiny elastin aggregates and disrupted elastic fibers. Organ cultures of aortic explants from rabbits with or without pancreatic elastase supplementation for 5 days disclosed that there was complete loss of medial elastic fibers and increasing deposition of microfibrils, morphologically identical to elastin-associated microfibrils, around viable smooth muscle cells only in the elastase supplemented group. These observations suggest that abnormal accumulation of microfibrils in the elastic tissue is closely associated with excessive elastolysis of preformed or newly formed elastic fibers during elastic tissue remodeling. Enhanced synthesis of microfibrils may occur in response to elastolysis as a reparative phenomenon.