CALCIUM-CARBONATE CRYSTALS PROMOTE CALCIUM-OXALATE CRYSTALLIZATION BYHETEROGENEOUS OR EPITAXIAL NUCLEATION - POSSIBLE INVOLVEMENT IN THE CONTROL OF URINARY LITHOGENESIS

A large proportion of urinary stones have calcium oxalate (CaOx) as th e major mineral phase. In these stones, CaOx is generally associated w ith minor amounts of other calcium salts. Several reports showing the presence of calcium carbonate (CaCO3) and calcium phosphate in renal s tones suggested that crystals of those salts might be present in the e arly steps of stone formation. Such crystals might therefore promote C aOx crystallization from supersaturated urine by providing an appropri ate substrate for heterogeneous nucleation. That possibility was inves tigated by seeding a metastable solution of Ca-45 oxalate with vaterit e or calcite crystallites. Accretion of CaOx was monitored by Ca-45 in corporation. We showed that (1) seeds of vaterite (the hexagonal polym orph of CaCO3) and calcite (the rhomboedric form) could initiate calci um oxalate crystal growth; (2) in the presence of lithostathine, an in hibitor of CaCO3 crystal growth, such accretion was not observed. In a ddition, scanning electron microscopy demonstrated that growth occurre d by epitaxy onto calcite seeds whereas no special orientation was obs erved onto vaterite. It was concluded that calcium carbonate crystals promote crystallization of calcium oxalate and that inhibitors control ling calcium carbonate crystal formation in Henle's loop might play an important role in the prevention of calcium oxalate stone formation.