Modifiers of calcium oxalate crystallization found in urine. I. Studies with a continuous crystallizer using an artificial urine

Abstract

Various modifiers of the rate of crystallization of calcium oxalate (CaOx) known to be present in urine were studied in a continuous crystallizer system under conditions approximating those in whole urine. Of the small ions examined, magnesium and citrate were only weak inhibitors of the crystal growth rate and degree of agglomeration of CaOx within the urinary range of concentration of these ions. At and beyond the upper limit of the normal, however, both ions became much more active mainly through their ability to complex oxalate and calcium ions respectively. Pyrophosphate showed similar characteristics although its ability to act as an inhibitor at high concentrations was not due to complexation of calcium ions but to adsorption onto the crystal surface of the freshly generated CaOx crystals. The polyanionic inhibitors, chondroitin-4-sulphate, heparin and ribonucleic acid (RNA), also acted as adsorption inhibitors of growth and agglomeration. Of all the inhibitors tested RNA was the most active within the concentration range found in normal urine. Under the conditions of ionic strength employed, it was not possible to measure the effect of Tamm-Horsfall mucoprotein satisfactorily since it polymerized to form particles sufficiently large to interfere with the true crystal counts of CaOx in the test system.