ETIOLOGY OF CALCIUM-OXALATE NEPHROLITHIASIS IN RATS .2. THE ROLE OF THE PAPILLA IN STONE FORMATION

In kidneys of healthy rats submitted to a crystal-inducing diet (CID) with ethylene glycol (EG) and NH4Cl, the fate of retained crystals in the papillar region is studied during a recovery period of one, five o r ten days, as model system for human nephrolithiasis. Scanning electr on microscopy (SEM) shows, at papillary tips bulging into the calycine space, crystal masses covered either by the epithelium or a thin fibr ous veil, or by unidentified mobile cuboidal cells. After CID plus one or five days recovery, small sub-epithelial swellings are seen of lar ge sub-epithelial crystals at or around the papillary tip. After CID p lus ten days, massive sub-surface crystal-containing micrometer-sized stones are seen in which the presence of calcium is confirmed by X-ray microanalysis. The papillary tip of rats after a re-challenge with an oxalate load from 0.1 vol% EG for twelve or forty-two days shows mino r lesions. But a re-challenge with 0.3 vol% EG for thirty-seven days i nduces large sub-epithelial papillary millimeter-sized stones. The Von Kossa section staining converts the crystals into a black precipitate , but large peri-tubular or peri-vascular calcium deposits are absent. A new hypothesis about the etiology of an inductive calcium oxalate m onohydrate nephrolithiasis is formulated which differs from the one pr oposed by Randall based on his deductive human kidney studies.