ETIOLOGY OF CALCIUM-OXALATE NEPHROLITHIASIS IN RATS .1. CAN THIS BE AMODEL FOR HUMAN STONE FORMATION

Crystal retention is studied in a rat-model system as a possible mecha nism for the etiology of human nephrolithiasis. A crystal-inducing die t (CID) of ethylene glycol plus NH4Cl in their drinking-water is offer ed to healthy rats to generate intratubular crystals. Subsequently, th e fate of retained crystals is investigated by allowing the rats a tis sue recovery/crystalluria phase for three, five and ten days, respecti vely, on normal drinking water. The process of exotubulosis is observe d in cortex and medulla of aldehyde-fixed kidneys after three days rec overy. After five days, crystals are predominantly seen there in the i nterstitium. After ten days, cortex and medulla are virtually free of crystals. However, in the papillary regions after five and ten days re covery, three types of calcium oxalate monohydrate (COM) crystals are present: (1) free in the calycine space, (2) sub-epithelially located surrounded by interstitial cells within, and (3) covered by macrophage -like cells, outside the original papillary surface. After a CID plus three days recovery, a further thirty-seven days extra oxalate challen ge with solely 0.3 vol% ethylene glycol induced intratubular and inter stitial oxalate crystals. In the papillary region, large sub-epithelia l crystals are seen. However, no crystals are seen in kidneys from rat s given solely (0.5 or 0.8 vol. %) ethylene glycol for thirty days. An oxalate re-challenge retards crystal removal.