Short-chain fatty acids modify colonic motility through nerves and polypeptide YY release in the rat

Short-chain fatty acids (SCFAs) are recognized as the major anions of the l arge intestinal content in humans, but their effect on colonic motility is controversial. This study explores the colonic motor effect of SCFAs and th eir mechanisms in the rat. Colonic motility (electromyography) and transit time (plastic markers) were measured in conscious rats while SCFAs were inf used into the colon, either alone or after administration of neural antagon ists or immunoneutralization of circulating polypeptide YY (PYY). SCFA-indu ced PYY release was measured by RIA and then simulated by infusing exogenou s PYY. Intracolonic infusion of 0.4 mmol/h SCFAs had no effect, whereas 2 m mol/h SCFAs reduced colonic motility (36 +/- 3 vs. 57 +/- 4 spike bursts/h with saline, P < 0.05) by decreasing the ratio of nonpropulsive to propulsi ve activity. This resulted in an increased transit rate (P < 0.01). Neither alpha-adrenoceptor blockade nor nitric oxide synthase inhibition prevented SCFA-induced motility reduction. Intraluminal procaine infusion suppressed the SCFA effect, indicating that a local neural mechanism was involved. SC FA colonic infusion stimulated PYY release in blood. Immunoneutralization o f circulating PYY abolished the effect of SCFAs on colonic motility, wherea s exogenous PYY infusion partly reproduced this effect. SCFAs modify coloni c motor patterns in the rat and increase transit rate; local nerve fibers a nd PYY are involved in this effect.