EFFECT OF URINARY MACROMOLECULES AND CHONDROITIN SULFATE ON CALCIUM-OXALATE CRYSTALLIZATION IN URINE

After filtration and ultrafiltration (10 kD) of 24 hour urine specimen s from 12 healthy male subjects, calcium oxalate crystallization was i nduced in the filtered (FILTD) and ultrafiltered (UF) fractions by adm inistration of a sodium oxalate load. In addition crystallization was also induced in UF fractions to which physiological quantities of chon droitin sulphate (CHON) had been added (UF + CHON). The rate of calciu m oxalate crystallization was determined by measuring the rate at whic h turbidity increased. Crystal numbers and sizes were measured with a Malvern particle size analyzer and by scanning electron microscopy. Cr ystallization rates, crystal numbers and crystal sizes were generally lower in UF fractions than in FILTD fractions suggesting that urinary macromolecules are promoters of calcium oxalate crystallization. No in crease in crystallization rate, crystal numbers or sizes occurred when chondroitin sulphate was added to UF fractions, indicating that the p romoter activity of urinary macromolecules is not due to this particul ar glycosaminoglycan. On the contrary, crystallization rates were qual itatively lower in UF + CHON fractions than in UF fractions alone, sug gesting a possible inhibitory role for chondroitin sulphate in real ur ine. Scanning electron microscopy revealed that while aggregates were present in UF and FILTD fractions, they were absent in UF + CHON fract ions. This observation indicates that chondroitin sulphate might be an inhibitor of calcium oxalate crystal aggregation in real urine.