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 of20mM, 50mM, and 100mM 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 oftransit which was inversely proportional to SCFA chain length. In a separate experiment, infusion of 100mM acetic acid, the most potent SCFA, into an isolated ileal Thiry-Vella loop failed to accelerate transit of the test meal. Our results suggest that SCFAs accelerate transit via a local enteric reflex. Sub-Department of Gastrointestinal Physiology and Nutrition, University of Sheffield, Sheffield A Richardson A T Delbridge N J Brown R D E Rumsey NW Read Correspondence to: Dr R D E Rumsey, Department of Biomedical Science, University of Sheffield, Western Bank, Sheffield S10 2TN. Accepted for publication 23 April 1990 Infusion of emulsions of triglyceride and long chain fatty acids (LCFA) into the terminal ileum ofhuman volunteers delays transit of a test meal through the stomach' and small intestine2` and suppresses propagated motor activity in the small intestine.5 A similar phenomenon can be shown in the rat; we have recently shown that infusion of long chain fatty acids (C14, C18, and C22) delays stomach to caecum transit time in that species.6 Recent studies have suggested that short chain fatty acids (SCFA) may act on the ileum to increase propulsive motor activity.78 The aim of this study was to investigate the effect of a range of SCFAs on the stomach to caecum transit time of a baked bean test meal in the rat, using a breath hydrogen technique modified for use with small mammals.9 TABLE I Electrolyte composition and osmolality oftest solutions Osmolality SCFA Saline PhosphatidylTaurocholic Glycerol (mOsmol/ (mM) (mM) choline (mM) acid (mM) (mM) kg) Acetic 20 154 320 50 154 382 100 154 442 Butyric 20 154 319 50 154 377 100 154 440 Hexenoic 20 140 16-8 9-4 9-1 335 50 140 16-8 9-4 9-1 360 100 140 16-8 9-4 9-1 382 Caprylic 20 140 16-8 9-4 9-1 325 50 140 16-8 9-4 9-1 325 100 140 16-8 9-4 9.1 335 SCFA=short chain fatty acid. Methods