Role of cecal pH in intestinal oxalate absorption in the rat

Hyperoxaluria occurs with many gastrointestinal disorders complicated by malabsorption. This hyperoxaluria is known to be the result of increased colonic absorption of dietary oxalate. Proposed mechanisms for this effect include alterations in fecal fatty acids, alterations in fecal bile acids, and acidification of colonic pH. Using an animal model of lactulose-induced chronic colonic acidification, we examined the effect of pH on oxalate absorption in vivo. Rats were fed a diet containing 6.77 mg oxalate per day with and without lactulose. Cecal pH of the animals receiving lactulose was significantly lower than controls (4.90 +/- 0.42 vs 7.17 +/- 0.38; p less than 0.001). Urinary excretion of oxalate was significantly greater in animals receiving the lactulose diet than in controls (0.975 +/- 0.144 vs 0.844 +/- 0.172 mg oxalate per day; p less than 0.001). These results demonstrate that acidification of the colon results in a significant increase in urinary oxalate excretion. Thus, acidification of the colon may be an important factor in the pathogenesis of enteric hyperoxaluria.