Effect of Maleic Acid on the Intestinal Uptake of Calcium and Oxalate in Pyridoxine-Deficient Rats

Calcium oxalate is the most common lithogenic substance found in human urinary calculi1. Hyperoxaluria has been observed in pyridoxine-deficiency and is presumably due to the increased endogenous synthesis of oxalate2,3 or to the increased bioavailability of dietary oxalate4,5. Oxalate uptake follows a biphasic transport mechanism. In vitamin B6-deficient rats, at low oxalate concentrations (0.1 to 0.8 mM), a saturable oxalate transport system (OTS) operates, while at higher concentrations of oxalate (0.8 to 6 mM), its uptake follows a passive diffusion mechanism5. Carrier-mediated OTS is inhibited by protein synthesis inhibitors and glycolate or glyoxylate competitively inhibits oxalate transport4. To understand the mechanism of this uptake process the effect of other mono- and dicarboxylic acids on the saturable oxalate transport system and calcium uptake in pyridoxine-deficient rats has been investigated.