Evaluation of the relative inhibitory potential of fractionated urinary macromolecules

Ultrafiltration membranes of 10,000 d, 1,000 d and 500 d were used to remove urinary macromolecules from the urine of normal subjects and from the urine of stone forming patients. The filtrated urines were examined for their residual inhibitory potential for calcium-oxalate precipitation, by the discrimination method of Sarig et al. (D.I. test). The results of testing the filtrate were complementary to the information gained by analyses of retentates obtained in successive ultrafiltration. The method has an inherent advantage because the manipulation of solids retained on membranes may inadvertantly modify their inhibitory potential. At least two distinct groups of inhibitors were found in 20 normal urines. The first group has MW above 10,000 d while the second group of inhibitors has MW in the range of 500-1,000 d. The mean of the D.I. values increased dramatically from the normal range (less than 0.6) to the stone former range (greater than 1.1) (p less than 0.001) after the 500 d filtration. Some of the normal urines, even after the 500 d filtration, still had a degree of inhibitory potential. This inhibitory potential may be related to the inorganic compounds which were found in the urines. The inhibitory activity of macromolecules with MW above 10,000 d and below 500 delta was negligible in 7 stone formers (SF) urines. The relative contribution of 500-1,000 d macromolecules is the highest both in SF and normal urines.

1) inhibitors in human urine are of wide range in MW; 2) stone formers and normals differ in the level of inhibitor activity at all MW ranges; especially in above 10,000 d and below inhibitors.