THE ULTRASTRUCTURAL CHANGES OF EXPERIMENTAL HYDROURETER IN RATS

Abstract

The ultrastructural changes of the epithelium and tunical muscularis of the ureter to urinary obstruction were examined in rats by transmission and scanning electron microscopy. Hydroureter was made by complete double ligation of the lowest part of the left ureter. The rats were in series sacrificed from 1 day to 20 weeks after ureteral ligation. The results obtained were as follows:
1) The normal ureter was lined by three to eight-layerd cells which were composed of superficial cells, intermediate cells and basal cells. The superficial cell had a scalloped free surface and many fusiform vesicles in the cytoplasm. The superficial cell was oblong in shape, the intermediate cell spindle and the basal cell cuboidal. The tunica muscularis was composed of closely packed smooth muscle cells which were characterised by abundant myofilaments and many dense bodies. There were scattered collagen fibers in the intercellular space.
2) Within 3 days after ligation, lipid droplets appeared and tonofilaments were accumulated in the epithelial cells. Smooth muscle cells showed cellular edema and had lysosomes. A considerable amount of fibrin was deposited in the intercellular space of the tunica muscularis.
3) From 5 days to 5 weeks after ligation, the epithelium was thickened and lined by three to eight-layered cells. The superficial cells became flat and the intermediate cells were provided with increased fusiform vesicles and slightly developed rough endoplasmic reticulum. The tunica muscularis became hypertrophic and the smooth muscle cells contained an increased number of mitochondria, well developed rough endoplasmic reticulum and Golgi apparatus.
4) More than 8 weeks after ligation, the epithelium bacame thinner down to 2, 3 or 4 layers and the intermediate cells were exposed to ureteral lumen. Myofibroblasts appeared in the tunica muscularis. Smooth muscle cells were extremely elongated and widely separated by the increase of the intercellular matrix. Myofilaments and dense bodies decreased in the cytoplasm of elongated smooth muscle cells and myofibroblasts.
The following suggestions were made from above observation: first; the epithelium accommodated itself to extension of the ureter by thinning and sliding of the overlying cells, second; until 5 weeks after ligation, the tunica muscularis well responded to the increase of intraureteral pressure with hypertrophy of smooth muscle cells, third; the ureteral peristalsis was finally impaired by the decrease of myofilaments and dense bodies in smooth muscle cells and excessive increase of the intercellular matrix among smooth muscle cells.