The paradox of inhibition and enhancement of the formation of urinary stones.

Nucleation (Bo) and linear crystal growth (G) rates, average particle size (L1,0) and total mass (MT) of calcium oxalate dihydrate crystals were measured in artificial urine with and without polylysine, polyglutamic acid or heparin. The purpose of the study was to see if any of these polymers had effects on crystallisation similar to those created by addition of 5% natural urine to artificial urine, wherein Bo had increased but G, L1,0 and MT decreased. Polylysine addition had insignificant effects. Heparin increased Bo and decreased G, L1,0 and MT significantly, and polyglutamate had similar but more marked effects than did heparin. It is concluded that properly structured organic polymers can significantly inhibit calcium oxalate dihydrate crystallisation by paradoxical enhancement of nucleation. It is possible that such polymers may act as nucleation substrates.