THE ULTRASTRUCTURE OF ARTERIES PROXIMAL TO CHRONIC EXPERIMENTAL CAROTID-JUGULAR FISTULAE IN RABBITS

The afferent arteries from 11 normocholesterolemic rabbits with carotid-jugular arteriovenous fistulae ranging in duration from 107 to 718 days were examined by transmission electron microscopy to determine long term effects of an arteriovenous shunt on the afferent artery. Extensive tears and fragmentation of the internal elastic lamina of the elastic common carotid arteries were observed in all animals. Fragmentation and loss of elastic tissue as well as loss of muscle in the media accompanied progressive mural atrophy and tortuosity. Close to the fistula and in regions of tortuosity, fibromusculoelastic intimal proliferation was superimposed on the atrophic medial changes. The accumulation of matrix vesicles (cell debris), bizarre shaped smooth muscle cells, irregularly thickened multilaminated and reticulated basement membrane material beneath the endothelium and about smooth muscle cells, and abnormal shaped collagen fibrils were observed in the intima. Lipid was frequently found in the extracellular matrix and within smooth muscle cells while monocytes and lipid-laden macrophages were a feature of the more advanced intimal changes. These experiments confirm that in the absence of hypercholesterolemia the hydraulic stresses associated with an arteriovenous shunt cause severe mural atrophy and proliferative changes in the intima similar in nature to those of atherosclerosis.