Intestinal and renal handling of oxalate loads in normal individuals and stone formers

The renal handling and intestinal absorption of dietary oxalate are believed to be risk factors for calcium oxalate stone formation. In this study, we have examined the time and dose effects of soluble oxalate loads on the intestinal absorption and renal handling of oxalate in six stone formers (SF) and six normal individuals (N) who consumed diets controlled in oxalate and other nutrients. Urinary and plasma oxalate changes were monitored over 24 h after ingestion of 0, 2, 4, and 8 mmole oxalate loads, containing a mixture of ¹²C- and ¹³C₂-oxalate. There were significant time and dose dependent changes in urinary oxalate excretion and secretion after these loads. However, there were no significant differences between SF and N in both the intestinal absorption and the renal handling of oxalate loads, as measured by the urinary excretion of oxalate (P = 0.96) and the ratio of oxalate to creatinine clearance (P = 0.34). ¹³C₂-oxalate absorption studies showed three of the subjects, two SF and one N, had enhanced absorption with the 8 mmole load. A clear difference in absorption was demonstrated in these individuals during the 8–24 h interval, suggesting that in these individuals there was greater oxalate absorption in the large intestine as compared to the other subjects. This enhanced absorption of oxalate warrants further characterization.