[Oxalic acid metabolism in chronic renal failure]

The mean plasma oxalic acid level is increased in renal failure. The mean plasma oxalic acid level was 74.8 +/- 18.5 mumol/l in 15 patients with chronic renal failure and 129.9 +/- 47.7 mumol/l in 31 patients on chronic haemodialysis which are several times higher than the normal range (16.8 +/- 6.0 mumol/l). During haemodialysis oxalic acid showed a behaviour similar to that of creatinine. The increased plasma oxalic acid levels are due to the accumulation of oxalic acid in renal insufficiency and additional metabolic factors increasing endogenous synthesis of oxalic acid. The administration of pyridoxine caused a decrease of the mean plasma oxalic acid level by 46% (32.0 to 56.1%) in 6 out of 8 chronic haemodialysis patients. This occurred most probably by correcting a vitamin B6 deficiency. Investigations of the intraerythrocyte glutamic oxalacetic transaminases showed, that the action of pyridoxine therapy on the endogenous oxalic acid synthesis can be explained by an increase of available pyridoxal-5-phosphate, the active metabolite of vitamin B6. The administration of vitamin B1, however, caused no statistically significant decrease of the plasma oxalic acid levels. Other influences on plasma oxalic acid synthesis result from the diminished excretion of the precursors of oxalic acid glycolic acid and ascorbic acid. The conversion of glycolic acid to glycine is probably increased in uraemia. The administration of 1 g ascorbic acid after each haemodialysis caused a striking increase of the plasma oxalic acid levels up to 240% of the initial value within 2 weeks, as a consequence of an increased metabolism of accumulated ascorbic acid. Increased plasma oxalic acid levels seem to be an important factor for calcium oxalate deposits in uraemia.(ABSTRACT TRUNCATED AT 250 WORDS)