Inhibition of calcium oxalate monohydrate (COM) crystal growth by pyrophosphate, citrate and rat urine.

An assay system for the measurement of the rate of Calcium Oxalate Monohydrate (COM) seed crystal growth in a metastable solution of calcium chloride and sodium oxalate containing traces of 14C-oxalic acid was used to assess the inhibitory activity of pyrophosphate (10(-5) M-10(-4) M), citrate (10(-4) M-10(-3) M) and urines of normal and pyridoxine deficient rats. Both pyrophosphate and citrate were strong inhibitors of COM crystal growth and caused a 50% decrease in crystal growth rate at 1.50 X 10(-5) M and 2.85 X 10(-4) M respectively. Normal rat urine strongly inhibited the COM crystal growth, while pyridoxine deficient animals showed a significant (p less than 0.01) decrease in mean inhibitory activity as compared to pair-fed controls. A lowered urinary inhibitory potential accompanied with hyperoxaluria and hypercalciuria, which is known to be associated with pyridoxine deficiency, may be a contributory risk of calcium oxalate crystallization and stone formation.