A MODEL SYSTEM FOR THE INVESTIGATION OF URINARY STONE FORMATION

Objective To develop an in vitro model system for the investigation of calcium oxalate urinary stones under conditions of spontaneous precip itation. Materials and methods Using a calcium-ion selective electrode and automatic titrator, a test solution was kept supersaturated with calcium oxalate and the rate of crystallization measured. Results Duri ng the spontaneous precipitation at constant supersaturation at 37 deg rees C, the induction times required for the precipitation of calcium oxalate monohydrate were inversely proportional to the supersaturation of the solution. No transient phases were identified and the interfac ial energy determined from kinetic analysis was 28.4 mJ/m(2). The rate s of precipitation showed a first-order dependence on the degree of su persaturation and were in good agreement with those reported for the i n vivo formation of calcium oxalate monohydrate stones. Conclusion Thi s experimental model system allows precise measurements of the kinetic s of calcium oxalate monohydrate. From the dependence of the rates of precipitation on supersaturation, a mechanism controlled by surface di ffusion is suggested.