Calcium oxalate precipitation in a flow system: an attempt to simulate the early stages of stone formation in the renal tubules.

This paper describes in vitro studies on the generation of supersaturation and the early stages of calcium oxalate (CaOx) precipitation using a reverse osmosis hollow-fiber membrane to simulate the precipitation processes occurring in the distal convoluted tubule and the collecting system of the kidney. The article reports on the preliminary results of using a plug-flow configuration to simulate the reabsorption of water and generation of supersaturation during the approximately three-minute biological residence time of the urine in the upper part of the urinary tract. The results suggest that microcrystallization of CaOx . 2H2O in the renal tubules may play a role in stone formation processes. A survey of the effect of various inhibitors of CaOx precipitation indicates that pyrophosphate, magnesium, glutamic acid, heparin and citric acid reduce the tendency of CaOx crystals formed to agglomerate in this system.