Review Article: Intestinal Serotonin Signalling in Irritable Bowel Syndrome

G. M. Mawe; M. D. Coates; P. L. Moses

Disclosures

Aliment Pharmacol Ther. 2006;23(8):1067-1076. 

In This Article

Evidence for Altered Serotonin Signalling in IBS

It is becoming increasingly clear that changes in 5-HT signalling occur in IBS. Due to the importance of 5-HT as an intercellular signalling molecule in intrinsic and extrinsic gut reflexes, various elements of 5-HT signalling have been evaluated to determine whether it is altered in IBS.[5,13,14,15,16,17] These include EC cell numbers, TpH message levels, 5-HT content, 5-HT release, SERT immunoreactivity, SERT message levels and platelet-free serum 5-HT levels. The findings of these studies are summarized in Table 1 , Table 2 , and Table 3 .

A common feature of the studies conducted to date is that they have all reported changes in one or more aspects of 5-HT signalling in IBS. However, the results of these investigations are not entirely in harmony. For example, various combinations of changes in EC cell populations and 5-HT content have been reported in the different forms of IBS. One of these studies reported that no changes in 5-HT release were detected in IBS-D or IBS-C under basal or stimulated conditions.[5] If this finding reflects the physiological nature of 5-HT release in these individuals, it would indicate that the same amount of 5-HT is being released regardless of possible changes in EC cell numbers or 5-HT content, and therefore changes in 5-HT signalling upstream of release may be irrelevant. When interpreting data related to elements of 5-HT signalling downstream of 5-HT release, both consistencies and contradictions exist. In the case of IBS-D, Coates et al.[5] reported a decrease in SERT expression, indicating that the capacity of the epithelial cells to sequester locally released 5-HT would be compromised. Consistent with this, Dunlop et al.[15] reported an increase in serum 5-HT levels, which was also reported in IBS-D. On the other hand, a decrease in SERT expression was also reported in IBS-C whereas a decrease in serum 5-HT was observed in this form of IBS. Further studies will have to be conducted to validate the findings that have been reported to date and to resolve the discrepancies that exist.

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