Experimental model to study sedimentary kidney stones.

An experimental model to reproduce, to some extent, the conditions prevailing during the formation of the so-called sedimentary urinary stones, was developed. The results obtained demonstrated that in the absence of organic matter no calcium phosphate crystals were deposited in cavities with scarce liquid renovation. Nevertheless, in such case a regular hydroxyapatite layer was developed on the walls around the cavity. The presence of crystallization inhibitors cannot stop indefinitely the crystal development. Therefore, phytate manifested important inhibitory effects in concentrations normally found in urine (0.77-1.54 x 10(-6) mol/l), whereas citrate only manifested important inhibitory effects when found at high urinary concentrations (2.64 x 10(-3) mol/l). When mucin (a glycoprotein) was present in the urine, a clear deposit of calcified organic material was formed. The organic matter appeared mixed with the spherulites of hydroxyapatite, this demonstrating the capacity of the glycoprotein agglomerates to act as heterogeneous nucleants of calcium salts and their important role in the formation of sedimentary stones. The structural features of the obtained in vitro deposits were compared with the fine structure of human sedimentary phosphate calculi. Scanning electron microscopy images demonstrated a good correspondence between in vitro experiments and in vivo observations.