Acid microclimate in coeliac and Crohn's disease: a model for folate malabsorption.

The surface pH of human proximal jejunum was measured in biopsy samples and found to be more acid than the phosphate buffer in which they were incubated. The in vitro jejunal surface pH was 5.93 +/- 0.05 in control subjects and 6.19 +/- 0.09 in treated coeliac patients. A group of untreated coeliac patients with a surface pH of 6.56 +/- 0.14 had a significantly less acid surface pH compared to controls, as did a group of Crohn's patients with a surface pH of 6.21 +/- 0.04. These two groups with a significantly raised surface pH were subdivisible into 'high' and 'low'groups. Surface pH was found to remain low in the treated coeliac and control groups but became more acid over the incubation period reaching almost normal values in the Crohn's group and the untreated coelic initial surface pH. The raised surface pH in untreated coeliac disease and Crohn's disease would alter the amount of a weak acid available for non-ionic diffusion. Therefore the present results may help to explain the folate malabsorption known to occur in untreated coeliac disease and the frequently seen low serum folate levels in Crohn's disease.