Renal and Intestinal Handling of Oxalate following Oxalate Loading in Rats

Background: The enteric excretion of oxalate has been established in rats with chronic renal failure induced by 5/6 nephrectomy [Hatch et al.: Regulatory aspects of oxalate secretion in enteric oxalate elimination. JASN 1999;10:S324] and this response is mediated by angiotensin II receptor activation. However, the renal and intestinal handling of oxalate has not been evaluated for other common models of hyperoxaluria that simulate primary hyperoxaluria or oxalate stone disease. Methods: We assessed the renal clearances of creatinine, oxalate and calcium in three rat models: chronic hyperoxaluria (CH), chronic hyperoxaluria with hyperoxalemia (CHH) and acute hyperoxaluria (AH), and evaluated the transepithelial transport of oxalate and chloride in large intestinal segments of these models and their sensitivity to angiotensin II antagonism. Results: Hyperoxaluria alone (CH) was not associated with changes in colonic oxalate transport, whereas changes in net oxalate transport in distal colon from absorption to net secretion was observed in models with hyperoxalemia (CHH and AH). Angiotensin II receptor antagonism with losartan reduced net colonic oxalate secretion in AH but not CHH. Conclusions: Colonic secretion of oxalate is stimulated in rat models exhibiting hyperoxalemia suggesting a contribution of this extrarenal pathway to regulation of oxalate mass balance in clinical conditions manifesting hyperoxalemia. The transport avenues and regulatory mechanisms may not be identical to those observed during adaptive enteric oxalate secretion in chronic renal failure models.