Intestinal excretion of oxalate in chronic renal failure.

The extrarenal elimination of oxalate via the intestine was studied in rats with chronic renal failure by measuring the magnitude and direction of oxalate fluxes across the small and large intestine. Oxalate transport was determined in vitro across short-circuited sheets of jejunum, ileum, and colon that were placed in Ussing chambers. The concentration of oxalate in plasma and urine was measured immediately before the transport studies. The results show that, 6 wk after 5/6 nephrectomy, rats with chronic renal failure have lower (decreases 50%) renal clearance of oxalate and a higher mean plasma oxalate concentration (increases 80%) than controls. The basal absorption of oxalate across the colon was changed to secretion in animals with chronic renal failure (from 12.81 +/- 2.22 (N = 9) to -14.96 +/- 2.57 (N = 11) pmol/cm2 per hour). Both the jejunum and the ileum supported a basal net secretory flux of oxalate (-19.71 +/- 2.39 (N = 13) and -30.06 +/- 2.80 (N = 16) pmol/cm2 per hour) that was unaffected by renal insufficiency. These studies demonstrate that intestinal transport systems for oxalate are altered in experimental chronic renal failure, and the distal colon is identified as the primary site for this adaptive response. In chronic renal failure, the entire intestinal tract can potentially excrete oxalate.