Serotonin synthesis and uptake in symptomatic patients with Crohn's disease in remission

Symptoms resembling irritable bowel syndrome (IBS) are reported frequently in Crohn's disease (CD) patients in remission. Studies of the mucosal content of serotonin, which is a pivotal neurotransmitter in the gut, suggest that serotonin availability is altered in IBS patients. We aimed to study the role of serotonin in the generation of IBS-like symptoms in CD patients in remission.

Ileal and colonic biopsy specimens were obtained from 20 CD patients in remission, 10 with and 10 without IBS-like symptoms, and 11 healthy controls. Enterochromaffin cells were counted, and messenger RNA expression levels of tryptophan hydroxylase (TpH)-1 and serotonin reuptake transporter were determined.

The levels of mucosal serotonin reuptake transporter expression were significantly higher in the ileum than in the colon, in all groups studied (P < .02). When the ileum and colon were analyzed separately, TpH-1 expression in the colon of CD patients with IBS-like symptoms was found to be significantly higher compared with the 2 other studied groups (controls, P < .005; CD patients without IBS-like symptoms, P < .01). The number of enterochromaffin cells per gland was comparable for the patient groups in the ileum and colon.

CD patients in remission who experience IBS-like symptoms have increased mucosal TpH-1 levels in the colon, suggesting that increased serotonin biosynthesis in the colon plays a role in the generation of the symptoms.