Changes in number of serotonin-containing cells and serotonin levels in the intestinal mucosa of rats with colitis induced by dextran sodium sulfate.

The role of serotonin in the pathogenesis of inflammatory bowel disease has not been fully studied. We examined the changes in the serotonin level and the density of serotonin-containing enterochromaffin (EC) and mast cells in the intestinal mucosa of dextran sodium sulfate (DSS)-induced colitis in rats. Rats were treated with 1.5% DSS for 1 month. Serotonin levels were biochemically measured and the density of epithelial EC cells and mucosal mast cells was quantified by serotonin immunohistochemistry. DSS caused malnutrition due to chronic diarrhea. Infiltrated inflammatory cells were microscopically observed in the colonic wall with intact epithelium. The serotonin content in the mucosa/submucosa tissue was increased in the proximal and distal colon in DSS-treated rats, compared to that in control rats. The density of EC cells in the epithelium also increased in the proximal and distal colon in DSS-treated rats. In contrast, the density of mast cells in the lamina propria dramatically increased in the distal, but not in the proximal colon in DSS-treated rats. This discrepancy implies the serotonin released from EC cells and from mast cells may play different roles in the pathogenesis of DSS-induced colitis.