The formation of oxalate from hydroxypyruvate, serine, glycolate and glyoxylate in the rat.

[14C]Oxalate was found in the urine of fasted male Wistar rats fed L-[14C3]-serine, DL-[14C1]serine, [14C1]ethanolamine, [14C1]hydroxypyruvate, [14C3]-hydroxypyruvate, [14C1]glycolate or [14C2]glyoxylate. [14C1]Hydroxypyruvate and [14C1]ethanolamine were the least effective precursors of [14C]oxalate. 20% of the [14C1]serine and [14C3]serine administered was recovered as 14CO2, while less than 4% was metabolized by pathways known to contribute to oxalate synthesis. Oxalate synthesis from serine involved both the transamination to hydroxypyruvate and the conversion to glycine, but not decarboxylation to ethanolamine. The oxidation of [14C2]glyoxylate to [14C]oxalate in the rat was inhibited by hydroxypyruvate, but the oxidation of [14C1]glycolate to [14C]-oxalate was not significantly altered. [14C]Glycolaldehyde, [14C]glycolate, [14C]glyoxylate and [14C]oxalate were recovered in the urine of rats administered [14C3]hydroxypyruvate. This is consistent with the oxidation of hydroxypyruvate via glycolaldehyde leads to glycolate leads to glyoxylate leads to oxalate and is identical to the metabolic pathway for the oxidation of ethylene glycol to oxalate. However, the major metabolic intermediate recovered from [14C3]hydroxypyruvate was [14C]glyoxylate rather than [14C]glycolate, suggesting that an alternate pathway is contributing to the oxidation of hydroxypyruvate to oxalate in the rat.