Short-Chain Fatty Acids,Lactate,and Ammonia in Ileorectal and Ileal Pouch Contents: A Model of Cecal Fermentation

Abstract

Fecal concentrations of total short-chain fatty acids were normal in 16 patients with ileorectal anastomoses (mean ± SEM, 99.7 ± 10.3 mmol/L) and 28 patients with ileal pouch-anal anastomoses (138.8 ± 8.5 mmol/L) and did not differ from those in 14 healthy noncolectomized controls (130.7 ± 12.6 mmol/L). Acetate:propionate:butyrate:isobutyrate+ valerate+isovalerate ratios were similar in the ileorectum (71:12:12:5%) and in the colorectum (66:14:13:7%) of healthy noncolectomized controls, whereas the concentration of acetate was increased at the expense of the polypeptide-derived isobutyrate, valerate, and isovalerate in the ileal pouch (77:12:11:1%). Ammonia was accordingly significantly diminished in ileal pouch contents (28.8 ± 3.2 mmol/L us 45.2 ± 4.1 mmol/L in controls) in contrast to concentrations in ileorectal contents (36.2 ± 5.3 mmol/L). Concentrations of lactate were normal and low. Twenty-four-hour productions of total short-chain fatty acids in 16.6% fecal homogenates from both groups of patients were normal. Addition of saccharides (eg, glucose, starch, pectin, ispaghula husk) increased the production of acetate, propionate, and butyrate and decreased the production of ammonia and isobutyrate, valerate, and isovalerate, which was increased in homogenates with albumin added. This pattern of substrate fermentation was similar in homogenates from ileal pouch, ileorectum, and control colorectum. In conclusion, the concentrations of short-chain fatty acids, lactate, and ammonia indicate that ileorectal fermentation resembles normal colorectal fermentation in noncolectomized healthy individuals, whereas the fermentation in ileal pouch contents seems to be more carbohydrate predominated. Therefore, although the ileorectum and ileal pouch are both positioned close to the incoming small intestinal digesta, the ileal pouch may serve as a more appropriate in vivo model of cecal fermentation than the ileorectum. (Journal of Parenteral and Enteral Nutrition 17:324-331, 1993)