Light and scanning electron microscopic studies of oxamide urolithiasis in rats.

The formation of urinary oxamide stones was induced in rats by feeding them oxamide mixed with powdered rat chow. The structure of these stones and the changes in the rat renal papillary structure following oxamide administration were studied using bright field and polarizing light microscopy as well as scanning electron microscopy. Oxamide appeared in the papillary collecting ducts, pelvis, ureters and urinary bladder of the rats in the form of yellow spherulitic units composed of dendritic crystals. Oxamide stones in turn were aggregates of these spherulites. Our results indicate the renal stone formation started with the crystallization of oxamide in the tubular lumina of the collecting ducts of the papillae. Crystal formation in the tubules was associated with epithelial necrosis. Some of the crystals became attached to injured epithelium, thus impeding urinary flow. The attachment of the crystals resulted in their retention in the renal tubules. These oxamide deposits then grew or aggregated to form stones. The formation of oxamide deposits in the ducts of Bellini resulted in dilatation, compression of the epithelium and destruction of the papillary urothelium. These factors resulted in the deformation of the papillary tip of the kidney.