Short chain fatty acids in the terminal ileum accelerate stomach to caecum transit time in the rat

We have previously shown that infusion of triglycerides and long chain fatty acids into the ileum of humans and rats delays small bowel transit time. The present studies have investigated the effect on the stomach to caecum transit time of a baked bean meal of the ileal infusion of 20 mM, 50 mM, and 100 mM acetic, butyric, hexenoic, and caprylic acids in rats. After an 18 hour fast either a control or a short chain fatty acid (SCFA) solution (pH 6.5) was infused into the ileum for 30 minutes (0.3 ml/hour). A test meal was given by gavage and the infusion continued for a further 150 minutes. The arrival of the meal in the colon was signalled by a rise in the exhaled hydrogen concentration. Acetic acid (20 mM, 50 mM, 100 mM), butyric acid (100 mM), and caprylic acid (100 mM) produced a significant acceleration of transit which was inversely proportional to SCFA chain length. In a separate experiment, infusion of 100 mM acetic acid, the most potent SCFA, into an isolated ileal Thirty-Vella loop failed to accelerate transit of the test meal. Our results suggest that SCFAs accelerate transit via a local enteric reflex.