The use of SEM in the study of oxalate induced experimental nephrolithiasis

The formation of calcium oxalate crystals in rat kidneys was induced by intraperitoneal challenge with sodium oxalate. The structure of these crystals and the effect of their formation on the architecture of the tubular epithelium was studied by SEM. From the results we conclude that the crystals were formed intraluminally in the renal tubules. During the growth of the microliths they were closely adherent to the luminal surface of the tubular epithelial cells. Two types of the crystals were identified. Calcium oxalate monohydrate crystals consisted of plate-like crystallites and were more common. Dihydrate crystals on the other hand were tetragonal dipyramids and were less common. Elemental analysis of the crystal surface revealed them to be closely similar to the crystals present in calcium oxalate stones. The renal tubules were morphologically altered. Their epithelial cells underwent focal necrosis. There was a focal loss of the microvillous brush border of the proximal tubules. The epithelial cells formed large blebs which protruded into the tubular lumen. Sometimes the tubular lumen was completely occluded by the crystals. Crystals were often covered with cellular debris. It is suggested that the cellular debris derived from from necrotic cells become incorporated into the calculi. A similar process may be involved in the formation of mucoproteinaceus matrix of the human renal stones.