Urinary oxalate, glycolate, glyoxylate, and citrate after acute intravenous administration of glyoxylate in rats

Background and Purpose: Urinary oxalate plays an important role in the form ation of calcium oxalate renal stones, and approximately 50% to 60% of urin ary oxalate is derived from the endogenous metabolism of glyoxylate, Theref ore, we measured urinary oxalate, glycolate, glyoxylate, and citrate concen trations after acute intravenous administration of various doses of glyoxyl ate in rats to study oxalate metabolism. Materials and Methods: Male Wistar rats weighing approximately 200 g were d ivided into six groups of eight animals each. Anesthetized rats received gl yoxylate (0, 1, 2, 5, 10, and 20 mg) intravenously, Urine specimens were co llected before and every hour after each dose for 4 hours, and the concentr ations of oxalate, glycolate, glyoxylate, and citrate were measured by capi llary electrophoresis, Results: Hourly oxalate excretion in the urine peaked at 1 hour after glyox ylate administration, and the peak concentration increased in a dose-depend ent manner. Approximately 15% to 30% (mol/mol) of the dose was converted to oxalate within 4 hours and 2% to 4.6% was converted to glycolate, Urinary glyoxylate was not detectable before glyoxylate administration, but large d oses resulted in a significant amount of glyoxylate (0.7%-2.3%) appearing i n the urine, and the level peaked at 1 hour after administration. Urinary g lycolate also peaked at 1 hour after administration of glyoxylate, The urin ary citrate concentration generally decreased by 3% to 33% after each dose of glyoxylate, except that it increased slightly after the 20-mg dose. Conclusion: Administration of glyoxylate increased urinary oxalate and glyc olate excretion in rats, supporting the importance of the glycolate-glyoxyl ate-oxalate pathway.