Gastroenterology

Gastroenterology

Volume 142, Issue 4, April 2012, Pages 844-854.e4
Gastroenterology

Original Research
Basic and Translational—Alimentary Tract
Activation of Colonic Mucosal 5-HT4 Receptors Accelerates Propulsive Motility and Inhibits Visceral Hypersensitivity

https://doi.org/10.1053/j.gastro.2011.12.041Get rights and content

Background & Aims

5-hydroxytryptamine receptor (5-HT4R) agonists promote gastrointestinal motility and attenuate visceral pain, but concerns about adverse reactions have restricted their availability. We tested the hypotheses that 5-HT4 receptors are expressed in the colonic epithelium and that 5-HT4R agonists can act intraluminally to increase motility and reduce visceral hypersensitivity.

Methods

Mucosal expression of the 5-HT4R was evaluated by reverse-transcriptase polymerase chain reaction and immunohistochemical analysis of tissues from 5-HT4R(BAC)-enhanced green fluorescent protein mice. Amperometry, histology, and short-circuit current measurements were used to study 5-HT, mucus, and Cl secretion, respectively. Propulsive motility was measured in guinea pig distal colon, and visceromotor responses were recorded in a rat model of colonic hypersensitivity. 5-HT4R compounds included cisapride, tegaserod, naronapride, SB204070, and GR113808.

Results

Mucosal 5-HT4 receptors were present in the small and large intestines. In the distal colon, 5-HT4 receptors were expressed by most epithelial cells, including enterochromaffin and goblet cells. Stimulation of 5-HT4Rs evoked mucosal 5-HT release, goblet cell degranulation, and Cl secretion. Luminal administration of 5-HT4R agonists accelerated propulsive motility; a 5-HT4R antagonist blocked this effect. Bath application of 5-HT4R agonists did not affect motility. Oral or intracolonic administration of 5-HT4R agonists attenuated visceral hypersensitivity. Intracolonic administration was more potent than oral administration, and was inhibited by a 5-HT4R antagonist.

Conclusions

Mucosal 5-HT4 receptor activation can mediate the prokinetic and antinociceptive actions of 5-HT4R agonists. Colon-targeted, intraluminal delivery of 5-HT4R agonists might be used to promote motility and alleviate visceral pain, while restricting systemic bioavailability and resulting adverse side effects.

Section snippets

Materials and Methods

See Supplementary Materials and Methods section for details of immunohistochemistry protocols, strains and sources of animals used, and physiological solution recipes and reagents.

Murine mucosal 5-HT4R expression

To assess the presence and relative levels of 5-HT4R transcript throughout the GI tract, real-time quantitative RT-PCR was performed in samples from the gastric corpus, duodenum, jejunum, ileum, and proximal and distal colons of SW and BALB/cJ mice. In full-thickness preparations, 5-HT4R transcript was detected from all regions, and when normalized to the endogenous control Hprt1, significantly higher levels were found in the distal and proximal colon as compared with more proximal regions of

Discussion

This study was performed to test the hypotheses that 5-HT4Rs are expressed in the colonic mucosa, and, when activated, promote propulsive motility and attenuate visceral hypersensitivity. Our findings provide novel molecular, morphologic, and physiological evidence for 5-HT4R expression in the colonic epithelium of mouse, rat, guinea pig, and human beings. Expression of this receptor was found on serotonin-containing EC cells and mucin 2–immunoreactive goblet cells, and activation of mucosal

Acknowledgments

The authors would like to thank Dr Brigitte Lavoie for consultation during the project, and Marion France for supplying electrodes for the mouse amperometry studies. The authors also would like to thank Drs Nathaniel Heintz and Eric Schmidt of Rockefeller University for 5-HT4R(BAC)-eGFP mouse tissue samples, and Drs John McRorie and Russell Spruell of Proctor and Gamble for 5-HT4R agonists.

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    Conflicts of interest The authors disclose no conflicts.

    Funding This work was supported by National Institutes of Health grants DK62267 (G.M.M.) and R21HD056197 (B.G.V.M.), and P20 RR16435 from the Centers of Biomedical Research Excellence (COBRE) Program of the National Center for Research Resources, as well as a grant from the Canadian Institutes of Health Research (K.A.S.); Sarah MacEachern is supported by the Dr. T. Chen Fong Doctoral Scholarship in Neuroscience through the Hotchkiss Brain Institute; and Keith Sharkey is an Alberta Heritage Foundation for Medical Research Medical Scientist and the Crohn's and Colitis Foundation of Canada Chair in IBD Research at the University of Calgary.

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