Study of the early stages of renal stone formation: experimental model using urothelium of pig urinary bladder.

An experimental model that enables the close simulation of conditions prevailing in the kidney during the formation of stones, using living tissue of pig urinary bladder, was developed. The results obtained clearly confirmed the importance of the antiadherent glycosaminoglycan (GAG) layer in preventing the development of solid concretions on the urothelium. Of importance was the capacity of the necrosed urothelium to act as a heterogeneous nucleant of calcium oxalate monohydrate (COM) and dihydrate (COD) crystals, demonstrating the major urolithiasic risk factor that alterations of the healthy epithelium covering the renal papilla may pose in humans. The significant increase in brushite and hydroxyapatite crystals detected on the urothelium when the pH of the artificial urine was 6.5, and the protective GAG layer was reduced or the tissue was necrosed, was also notable. The crystallization inhibitory effects caused by citrate and phytate were also studied. It was found that whereas citrate, at normal urinary concentrations, caused a slight reduction in crystallization, with phytate there was total elimination of crystallization-when it was present at very low concentrations such as 1.0 microgram/ml.