SUMMARY1. The contractile effect of short-chain fatty acids on proximal, middle and distal segments of the rat colon was studied in vitro. A single contraction of the longitudinal muscle of the everted preparation of the middle and distal but not the proximal colon was induced by mucosal application of propionate, butyrate or valerate.2. Sigmoid dose-responses were observed between contraction and log dose of propionate, butyrate and valerate. The threshold concentration of short-chain fatty acids was between 0-02 and 004 mm. A maximal contraction was induced with 01 mM-propionate, butyrate and valerate. While acetate (up to 10 mM) and lactate (up to 30 mm) had no contractile effect at all.3. Serosal application of short-chain fatty acids was without effect, while the contractile response with up to 10 mM-propionate was abolished in both the middle and distal colon by scraping away the mucosa.4. Cumulative addition of short-chain fatty acids to the organ bath (without wash-out of the first dose) caused adaptation of the contractile response; thus, the effect of propionate (1 mM) was abolished by prior addition of acetate (10 mM) or lactate (30 mM) or propionate (1 mM) or butyrate (1 mM) or valerate (1 mM).5. The contractile effect of propionate was also inhibited by atropine (1 ,uM), procaine (0 4 mM) and tetrodotoxin (3 /M); was unaffected by hexamethonium (041 mM) and enhanced by eserine (10 nM).6. The results suggest that short-chain fatty acids, which are normal constituents of the colon, have the ability to stimulate colonic contractions, probably via an enteric reflex involving local sensory and cholinergic nerves.

SUMMARYWe examined whether or not dietary fructooligosaccharides (FOS) in infancy can have a beneficial effect on the mucosal immune system. Newborn BALB/c mice, accompanied by their dams until 21 days of age, were fed either a control diet based on casein [FOS(-) diet group] or a FOS(-) diet supplemented with 5% (w/w) FOS [FOS(+) diet group]. Total IgA levels in tissue extracts from the intestines of mice in the FOS(+) diet group at 38 days of age were about twofold higher ( P < 0·05) than those in the FOS(-) diet group in the jejunum, ileum and colon. Ileal and colonic polymeric immunoglobulin receptor (pIgR) expression in the FOS(+) diet group at 36 days of age was 1·5-fold higher than in the FOS(-) diet group ( P < 0·05). Consistent with these results, the ileal IgA secretion rate of the FOS(+) diet group at 37 days of age was twofold higher than that of the FOS(-) diet group ( P < 0·05). Moreover, the percentage of B220 + IgA + cells in Peyer's patches (PP) was significantly higher in the FOS(+) diet group than in the FOS(-) diet group (6·2% versus 4·3%, P < 0·05), suggesting that isotype switching from IgM to IgA in PP B cells might be enhanced in vivo . Taken together, our findings suggest that dietary FOS increases the intestinal IgA response and pIgR expression in the small intestine as well as the colon in infant mice.

SUMMARY1. The stimulatory action of propionate on colonic electrolyte transport and involvement of the enteric reflex in this was studied in vitro using an Ussing chamber in the rat. The short-circuit current (I.,) and bidirectional fluxes of Na+ and Cl-were measured. Mucosa-submucosa preparations, containing the submucosal nerve, from the distal colon were used in most cases.2. Mucosal application of propionate caused transient increases in the transmural potential difference, with the mucosal side negative, ISc and conductance. Serosal application of the acid had no effect.3. Adaptation of the ISC response occurred when the acid was applied to the bathing solution cumulatively without washing out the first dose. If tissues were washed and held more than 20 min before the next application, the response was almost completely restored.4. The increase in IS. in response to propionate was concentration dependent, with a 50% effective concentration of approximately 7 x 10-5 M.5. Two other short-chain fatty acids (SCFAs), n-butyrate and n-valerate, but not acetate, increased ISC when added to the mucosal bathing solution.6. Bumetanide (3 x 10-5 M) and the serosal chloride-free condition, but not amiloride (10-M), inhibited the responses of ISC to propionate. Propionatestimulated Cl-secretion resulted mainly from an increase in unidirectional serosalto-mucosal C1-movement. Propionate did not affect the Na+ flux.7. Tetrodotoxin (10-7 M), somatostatin (10-7 M) and hexamethonium (10-4 M) inhibited the propionate-evoked increase in ISC by 40, 70 and 30°%, respectively.8. Atropine (10-5 M) also inhibited the I,,-increase response to propionate more than 90 %.9. Pre-treatment (2 min) of the mucosal surface with procaine (5 x 10-M)inhibited the propionate-evoked increase in IS. by 90°%.10. The results suggest that luminal propionate transiently stimulated the colonic chloride secretory response that is not due to direct action on colonocytes, but due in large part to release of acetylcholine at neuro-colonocyte junctions, probably via an enteric reflex involving a mucosal sensory mechanism, cholinergic motor nerves and submucosal ganglia.

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Hexose transporters play a pivotal role in the absorption of food-derived monosaccharides in the gastrointestinal tract. Although a basic knowledge of the hexose transporters has already been gained, their detailed distribution and comparative intensities of expression throughout the gastrointestinal tract have not been fully elucidated. In this study, we quantitatively evaluated the expression of SGLT1, GLUT1, GLUT2, and GLUT5 by in situ hybridization and real-time PCR techniques using a total of 28 segments from the gastrointestinal tract of 9-week-old mice. GLUT2 and GLUT5 mRNA expressions were detected predominantly from the proximal to middle parts of the small intestine, showing identical expression profiles, while SGLT1 mRNA was expressed not only in the small intestine but also in the large intestine. Notably, GLUT1 mRNA was expressed at a considerable level in both the stomach and large intestine but was negligible in the small intestine. Immunohistochemistry demonstrated the polarized localization of hexose transporters in the large intestine: SGLT1 on the luminal surface and GLUT1 on the basal side of epithelial cells. The present study provided more elaborate information concerning the localization of hexose transporters in the small intestine. Furthermore, this study revealed the significant expression of glucose transporters in the large intestine, suggesting the existence of the physiological uptake of glucose in that location in mice.