Influences of Short-Chain Fatty Acids on the Digestive Organs

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Abstract
Acetic, propionic, and n-butyric acids, called short-chain fatty acids (SCFA), are the major end-products of the hindgut fermentation. SCFA are rapidly absorbedacross the colonic mucosa and used as the nutrient. Luminal SCFA enhance the absorption of sodium and water. Bicarbonate accumulates in the hindgut lumen in proportion to the amount of SCFA absorbed in various animals. The buffering system of the bicarbonate accumulated into the lumen in response to SCFA absorption maystabilize the luminal pH. Propionic and n-butyric acids stimulate the colonic motility with an increased peristaltic propulsion of perfusate in the rat in vivo. Propionic, n-butyric, and n-valeric acids stimulate contractile response of the isolated segments of the rat colon in a dose-dependent manner. The contractile effect of SCFA on the rat colon does not act directly on the smooth muscle. The enteric nervous system may mediate the effect of SCFA, since the contractile responses were abolished by tetrodotoxin and atropine. The acute and chronic administration of SCFA (acetic, propionic, and n-butyric acid) into the hindgut of the rat enhanced the proliferation of the epithelium of the digestive tract in vivo.The stimulatory effect of SCFA is dose-dependent and is strong in order of n-butyric>propionic>acetic acids. Thus, SCFA are important not only as the nutrient but also as the modulator of electrolyte transport, motility, and epithelialproliferation of the digestive tract.