The effect of monosodium urate on the capacity of urine, chondroitin sulphate and heparin to inhibit calcium oxalate crystal growth and aggregation.

In order to investigate the possibility of interaction between urinary glycosaminoglycans and particulate monosodium urate, growth and aggregation rates of calcium oxalate seed crystals were measured in the presence of heparin, chondroitin sulphate and normal urine after preincubation with and without monosodium urate (0.5 mg./ml.). Rates of crystal aggregation in the presence of heparin and chondroitin sulphate were significantly (p less than 0.0005) increased after pretreatment with sodium urate, indicating a reduction in the inhibitory potency of heparin and chondroitin sulphate by this salt. A similar effect was observed with the rate of crystal growth in the presence of heparin (p less than 0.01). In contrast, the rate of growth in the presence of chondroitin sulphate was unaffected. Pretreatment with sodium urate had an inconsistent effect on the rate of crystal growth in the presence of 10 normal human urine samples, but significantly (p less than 0.001) raised the rate of crystal aggregation. It was concluded that the influence of urate on crystal aggregation in the presence of urine may be a result of its binding to endogenous chondroitin sulphate, but may not be of practical consequence in the pathogenesis of calcium oxalate renal stones.