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SCFA increase intestinal Na absorption by induction of NHE3 in rat colon and human intestinal C2/bbe cells.

Short-chain fatty acids (SCFA), produced by colonic bacterial flora fermentation of dietary carbohydrates, promote colonic Na absorption through mechanisms not well understood. We hypothesized that SCFA promote increased expression of apical membrane Na/H exchange (NHE), serving as luminal physiological cues for regulating colonic Na absorptive capacity. Studies were performed in human colonic C2/bbe (C2) monolayers and in vivo. In C2 cells exposed to butyrate, acetate, proprionate, or the poorly metabolized SCFA isobutyrate, apical membrane NHE3 activity and protein expression increased in a time- and concentration-dependent manner, whereas no changes were observed for NHE2. In contrast, no significant changes in brush-border hydrolase or villin expression were noted. Analogous to the in vitro findings, rats fed the soluble fiber pectin exhibited a time-dependent increase in colonic NHE3, but not NHE2, protein, mRNA, and brush-border activity. These changes were region-specific, as no changes were observed in the ileum. We conclude that luminal SCFA are important physiological cues for regulating colonic Na absorptive function, allowing the colon to adapt to chronic changes in dietary carbohydrate and Na loads.

Animals↗

Motor and absorptive function of the canine intestine following serosal patching: the effects of a lateral enterotomy on small intestinal myoelectrical activity.

We studied the effects of serosal patching of a 4 x 15-cm, full-thickness, jejunal defect on absorptive function and fasting and postprandial myoelectrical activity in 5 patched and 5 control animals over a 3-month period. While fat and D-xylose absorption were similar in both groups, serum albumin was significantly depressed (2.96 +/- 0.24 g/dL preop vs 2.29 +/- 0.23 g/dL postop, p less than .05) and stool moisture content was elevated following patching (54 +/- 4% vs 67 +/- 9%, p less than .05). Neither the generation of the various phases of the interdigestive myoelectrical complex (IDMEC), the development of postprandial myoelectrical activity, or colonic myoelectrical patterns were impaired in the patched animals. The normal gradients of slow wave frequency, phase III propagation velocity, and onset of the fed pattern were similar in control and patched animals. However, jejunal slow wave frequency (cpm, control vs patch: 18.6 +/- 0.6 vs 19.5 +/- 0.6, p less than .05) and IDMEC frequency (0.36 +/- 0.25 vs 0.56 +/- 0.32, p less than .05) were greater and the IDMEC period shorter (109.6 +/- 27.8 vs 88 +/- 35.7, p less than .05) in the patch animals. In vitro studies demonstrated similar absorptive function in intact mucosa and neomucosa. We conclude that the technique of serosal patching is associated with impaired absorption in vivo. While this may be related, in part, to the minor motility changes observed, other factors such as hormonal changes may also be important.

Animals↗