Proliferation and degeneration of elastic tissue in aortic explants from normo-, and hypercholesterolemic rabbits: An ultrastructural study

Abstract

Ultrastructural differences exist between the processes of elastogenesis and degeneration of elastic tissue in explants from normal aorta and in those from atherosclerotic lesions of rabbits maintained in culture for 10 days. In aortic explants from normal rabbits de novo formation was observed early and proceeded through the characteristic structural units which fused with each other and gave rise to larger elastic tissue elements—all having a typical filamentous appearance. Degeneration affected first the large lamellae and consisted of rarefaction of the interior and the surface with subsequent ingrowth of collagen fibrils. The structural integrity of the “young” elements was maintained to the end of the observation time. In the explants from lesions the newly formed units of elastic tissue showed subtle ultrastructural changes: there was an excess or paucity of the constituent microfibrils in relation to the homogeneous component. In either case the units were ill-defined and most of the larger elements lacked the filamentous inner structure. Degeneration largely proceeded through the gradual deposition in a segmental or islet-like pattern of finely crystalline substance (calcium compounds?) in the matrix of all, including the smallest elastic tissue elements. Ultimate disintegration of the tissues gave rise to round or oval, single or fused “shells” (tissue ghosts) with radially arranged crystalline substance. Whereas these changes have no known structural counterparts in the non-explanted aortic lesions or any other tissues, their basis may be inherent in the atherosclerotic process that becomes “unmasked” in the in vitro conditions of the present study.