Urinary in vitro sedimentation: effects of nondialyzable components and heparin

To determine whether nondialyzable urinary solids which are rich in hydroxyproline polypeptides, could act as nuclei in the formation of crystal aggregates, urine from patients with spinal cord injury (SCI) was pooled for 7 days and its nondialyzable fraction was separated and lyophilized. The ability of this extract to influence the formation of crystals was tested in vitro in a synthetic urine system. The concentrations of calcium, hydroxyproline, and uric acid, as well as the pH, were varied to simulate a range of possible situations in vitro. In the presence of the extracts, when the pH of the synthetic urine was increased from 5.5 to 6.5, the weight of the sediment decreased; in contrast, when the pH was increased from 7.0 to 8.5, the weight of the sediment increased. A similar synthetic urine system was used to test the effect of heparin, a medication often given SCI patients, on crystallization. In this instance, the pH was not altered. Heparin lowered the weight of sediments formed in solutions with uric acid concentrations of less than 50 mg/dl, but had varying effects in solutions with higher uric acid concentrations.