Effect of Short-chain Fatty Acids and Acidification on the Phasic and Tonic Motor Activity of the Human Colon

Background: The effects of bacterial fermentation on human colonic motor activity could be explained by colonic acidification or short-chain fatty acid (SCFA) production. We compared in healthy volunteers the colonic motor effects of intracolonic infusion of neutral or acidic saline solutions and then of neutral or acidic solutions containing an SCFA mixture.

Methods: 20 healthy volunteers swallowed a probe (with an infusion catheter, 6 perfused catheters and a balloon connected to a barostat) that migrated into the colon. Colonic motor activity was recorded in fasting basal state (1 h), during (3 h) and after (2 h) intracolonic infusion in a random order on two consecutive days of 750 mL of NaCl at pH 7.0 (neutral saline) or 4.5 (acidic saline) in 10 volunteers (first experiment) and of an SCFA mixture (acetic acid 66%, propionic acid 24% and butyric acid 10%; 100 mM) at pH 7.0 or 4.5 in 10 other volunteers (second experiment). We determined for each hour a global motility index (reflecting phasic activity recorded by all catheters), the mean balloon volume (reflecting tonic activity), and the mean number of high-amplitude-propagated contractions (HAPCs).

Key Results: Intracolonic infusion of neutral or acidic solutions containing saline or an SCFA mixture did not change the global motility index, the barostat balloon volume, or the HAPC number compared with basal values.

Conclusions & Inferences: Under our experimental conditions, these findings suggest that the stimulation of colonic motor activity induced by carbohydrate fermentation is not explained by the acidification of the colonic contents or the resulting production of SCFAs.