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Ultrastructure of the aorta in experimental uraemia.

The effect of chronic experimental uraemia on the ultrastructure of the aorta was studied in rats. Pathological changes were found essentially in the media, in which the smooth muscle cells commonly had increased amounts of endoplasmic reticulum, Golgi structures and mitochondria, probably reflecting an increased synthetic and metabolic activity. In other areas of the media, degenerative and necrotic changes of the smooth muscle cells dominated. Increased amountes of collagen and the appearance of vesicular structures, probably cell debris, were noted in the extracellular space. Diffusely spread needle- and plate-shaped electron dense structures were seen in some necrotic areas. By X-ray microanalysis these structures could be demonstrated to have a high content of calcium, and probably represented hydroxyapatite crystals. Two types of circumscribed rounded electron dense conglomerates also appeared. At least one of these structures, in which X-ray microanalysis showed a high calcium content, is thought to represent a site of early calcification. Electron dense deposits in the elastic structures were only occasionally seen. The alterations occurred in both parathyroidectomized and non-parathyroidectomized uraemic animals. The study revealed no signs of intracellular calcification and suggests a close relation between necrosis of the smooth muscle cells and calcification of the aortic wall in experimental uraemia.