Irritable bowel syndrome: a study to investigate the mechanism(s) of visceral hypersensitivity.

Irritable bowel syndrome (IBS), is characterized by gastrointestinal hyperalgesia. In this study we investigated mucosal application of dyclonine on urge to defecate and pain threshold in volunteers and IBS patients (n = 10). Either saline or dyclonine (40 ml enema) was administered 10 minutes prior to rectosigmoid distension or cutaneous cold water pressor test. In IBS patients and volunteers no differences in cutaneous pain thresholds were noted. However, IBS patients had a lower pain threshold in the rectosigmoid than volunteers. In volunteers there was a significant difference between the threshold for urge to defecate and the threshold for rectosigmoid pain that was not apparent in IBS patients. Dyclonine administered directly into the rectosigmoid did not alter urge to defecate or pain threshold induced by distension in volunteers or IBS patients. These data suggest that the origin of pain perception is localized in deeper structures within the wall of the rectosigmoid colon.