ETIOLOGY OF EXPERIMENTAL CALCIUM-OXALATE MONOHYDRATE NEPHROLITHIASIS IN RATS

In a rat-model system, tubular crystal retention as a possible mechani sm for the etiology of nephrolithiasis in man, was studied by conventi onal transmission electron microscopy. The animals were supplied for n ine days with a crystal-inducing diet, with ethylene glycol plus NH4Cl in their drinking-water. After this induction period, a two day regim e with fresh drinking-water was included, to allow crystals to be remo ved by spontaneous crystalluria. After aldehyde fixation of the rat ki dneys, large crystals were seen inside the tubular lumen. The crystals were attached to cell surfaces and covered by neighboring epithelial cells. Some crystals were overgrown by several epithelial cells and un derwent a process of so-called exotubulosis, resulting in free or cell -surrounded crystals in the interstitium, and possibly in crystals in Giant cells. To investigate the fate of the retained crystals, some an imals were additionally exposed to a low-oxalate challenge from drinki ng water containing 0.1 volume per cent of ethylene glycol for 12 or 3 0 days, respectively. It was assumed that this would interfere with th e retained intratubular or interstitial crystals, and allow the crysta ls to grow into mini-stones. This was not observed. After the oxalate challenge, no crystals were found to be retained in the tubules (free or covered by cells). Interstitial crystals were observed, but it rema ins to be demonstrated whether such crystals actually grow into mini-s tones or that they are removed by the sterile inflammation process obs erved.