Vascular changes in the brain of spontaneously hypertensive rats: hyaline and fibrinoid degeneration.

The arterial changes designated as "hyalinosis" in the vessels of spontaneously hypertensive rats were studied using light- and electron-microscopy. Such changes were classified into three types, hyaline, fibrinoid and atypical fibrinoid degeneration. Hyaline material consisted mainly of excessive lamellar thickening of the basement membrane synthesised by endothelial and smooth muscle cells and associated with cellular debris and electron-dense particles. Acid mucopolysaccharides were found to be one of the components of the hyaline material. The nature of fibrinoid material was primarily fibrin derived from polymerised fibrinogen which has permeated through the injured endothelial cell layer. Atypical fibrinoid material consisted of granular and fibrillar substances derived from blood plasma. In some cases, all three changes were encountered in the same artery.