Stimulation of ileal emptying by short-chain fatty acids.

We have shown previously that short-chain fatty acids (mixtures of acetic, propionic, and butyric acids; SCFAs) in the proportions found usually in stool water stimulate fasting ileal motility. Based on indirect evidence, we proposed that these motor patterns (bursts of phasic pressure waves that were propagated) would be propulsive, but the capacity of these stimulated patterns of motility to propel contents has not been established directly. Healthy, surviving dogs were provided with motility sensors and a cannula through which SCFAs could be instilled into the ileum. Boluses of SCFAs were much more likely to stimulate phasic bursts of motility than was saline. Scintigraphic studies using a gamma camera showed that the motility stimulated by SCFAs was propulsive and that the ileum was thereby emptied. We also tested whether SCFAs were equally effective stimuli during fasting and after food. SCFAs were equally effective during fasting and soon after food, but in the late postprandial period, when the meal reached the ileum, SCFAs were much less likely to stimulate motility. These observations shed further light on the capacity of the ileum to sense and react to the nature of the contents.