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APPETITE, OBESITY, DIGESTION, AND METABOLISM

Luminally released serotonin stimulates colonic motility and accelerates colonic transit in rats

¹Department of Surgery, Duke University Medical Center, Durham, North Carolina; and ²Second Department of Surgery, Hyogo College of Medicine, Nishinomiya, Japan

Submitted 8 December 2006 ; accepted in final form 31 March 2007

Enterochromaffin (EC) cells of the epithelial cells release 5-HT into the lumen, as well as basolateral border. However, the physiological role of released 5-HT into the lumen is poorly understood. Concentrations of 5-HT in the colonic mucosa, colonic lumen, and feces were measured by HPLC in rats. To investigate whether intraluminal 5-HT accelerates colonic transit, 5-HT and ⁵¹Cr were administered into the lumen of the proximal colon, and colonic transit was measured. To investigate whether 5-HT is released into the lumen, we used an ex vivo model of isolated vascularly and luminally perfused rat proximal colon. To investigate whether luminal 5-HT is involved in regulating stress-induced colonic motility, the distal colonic motility was recorded under the stress loading, and a 5-HT₃ receptor antagonist (ondansetron, 10^–6 M, 0.5 ml) was administered intraluminally of the distal colon. Tissue content of 5-HT in the proximal colon (15.2 ± 4.3 ng/mg wet tissue) was significantly higher than that in the distal colon (3.3 ± 0.7 ng/mg wet tissue), while fecal content and luminal concentration of 5-HT was almost the same between the proximal and distal colon. Luminal administration of 5-HT (10^–6–10^–5 M) significantly accelerated colonic transit. Elevation of intraluminal pressure by 10 cmH₂O significantly increased the luminal concentration of 5-HT but not the vascular concentration of 5-HT. Stress-induced stimulation of the distal colonic motility was significantly attenuated by the luminal administration of ondansetron. These results suggest that luminally released 5-HT from EC cells plays an important role in regulating colonic motility in rats.

enterochromaffin cells; distal colon; luminal pressure; restraint stress