RENAL TRANSPORT OF OXALATE - EFFECTS OF DIURETICS, URIC-ACID, AND CALCIUM

Clearance experiments were performed in the rat to examine the effects of diuretics on the renal transport of oxalate. In addition, the effect of infusing either uric acid or calcium on the renal transport of oxalate was examined. During control periods, the fractional excretion of oxalate (FEox) averaged 118.0 ± 21%. Acute administration of either chlorothiazide, furosemide, or indanyl-oxyacetic acid (MK-196), a new uricosuric diuretic, resulted in a significant decrease in the FEox in all groups to 104.8 ± 2.4%, 111.3 ± 2.1%, and 108.6 ± 2.7%, respectively. Infusion of uric acid increased urinary uric acid excretion from 2.41 ± 0.28 to 4.26 ± 0.03 μg/min/g kidney wt (P <0.001) and decreased FEox to 104.0 ± 2.4% (P <0.001 compared to control). Infusion of calcium chloride increased urinary calcium excretion from 0.10 ± 0.04 to 0.44 ± 0.06 μg/min/g kidney wt (P <0.001) but had no effect on the FEox which averaged 118.3 ± 8.3% (P = NS compared to control). These studies show that the acute administration of chlorothiazide, furosemide, or MK-196, as well as increasing urinary uric acid excretion by uric acid infusion, are all associated with a decrease in the FEox. Acutely increasing urinary calcium excretion, however, had no effect on oxalate transport.