Exaggerated motility of the descending colon with repetitive distention of the sigmoid colon in patients with irritable bowel syndrome.

BACKGROUND: Visceral hypersensitivity is one of the mechanisms of irritable bowel syndrome (IBS), but it does not explain the entire symptomatology, i.e., altered bowel habit with abdominal pain relieved by defecation. We tested our hypothesis that an abnormal link between luminal stimulation and mural response may have some role in the pathophysiology of IBS.
METHODS: Patients with IBS (n = 10, median 21 years old, 5 male patients, 5 female patients) and healthy control subjects (n = 10, median 21 years old, 5 men, 5 women) were studied. A manometric catheter with three transducers was inserted to the descending colon and a balloon was placed in the distal sigmoid colon. Another catheter with three transducers was inserted to the duodenum. After baseline for 30min, the sigmoid colon was stimulated by balloon distention for 30min followed by recovery for 30min. Balloon distention was repeated 100 times, and each stimulation consisted of a 5-s inflation and a 10-s deflation, with a volume of 50ml maximum. The sensory threshold of balloon inflation was then examined, and plasma adrenocorticotropic hormone (ACTH) was measured with radioimmunoassay.
RESULTS: Repetitive colonic distention induced a significant increase in motility indices (mmHg s/s%) of the descending colon in the IBS patients (from 118 +/- 25 to 333 +/- 108, P < 0.05) but not of those in controls (from 90 +/- 16 to 89 +/- 19). A significant group difference (P < 0.05), period effect (P < 0.02), and group x period interactions (P < 0.01) were detected with two-way ANOVA. Duodenal motility indices in controls were significantly reduced by colonic distention (from 169 +/- 25 to 104 +/- 14, P < 0.01), but those in the IBS patients were not (from 156 +/- 17 to 124 +/- 20). The sensory threshold of balloon inflation in the IBS patients (74 +/- 10ml) was significantly lower than that in controls (125 +/- 6ml, P < 0.001). There was no significant difference in plasma ACTH levels between the IBS patients and controls.
CONCLUSIONS: Repetitive distention of the distal sigmoid colon below the sensory threshold induced orad exaggerated motility of the colon in IBS patients. The distention inhibited motility of the small intestine in healthy subjects, but this inhibition was blunted in IBS patients. These results suggest that IBS patients may have not only visceral hypersensitivity, but also an abnormal intestinal reflex.