Visceral sensation and irritable bowel syndrome; with special reference to comparison with functional abdominal pain syndrome

Objective and Background: Stress-induced visceral hypersensitivity may play an important role in the pathogenesis of irritable bowel syndrome (IBS) but not in functional abdominal pain syndrome (FAPS). We examined rectal sensation in those patients. Methodology: Experiment 1: Rectal thresholds of pain (PT) and maximum tolerance were assessed by barostat with ramp distention before and after repetitive rectal painful distention (RRD). Experiment 2, PT was measured in basal state and after intravenous CRF (100 mu g) or vehicle, together with or without RRD. Experiment 3: Three phasic distentions at physiological range were randomly loaded. The subjects were asked to mark the visual analogue scale (VAS) in reference to subjective intensity of sensation. Results: Experiment 1: Majority of IBS patients showed rectal hypersensitivity before RRD in contrast to FAPS. All IBS patients developed hypersensitivity after RRD, however, none of the FAPS patients did. RRD significantly reduced both thresholds in IBS (n = 7) but did not change in controls (n = 14) and FAPS (n = 6). Experiment 2: PT was not modified by RRD in placebo group (n = 6), while it was significantly reduced in CRF-treated group (n = 5). On the other hand, CRF (n = 5) or vehicle (n = 5) without RRD did not alter PT. Experiment 3: The VAS ratings were increased in IBS (n = 7) but significantly decreased in FAPS (n = 6) as compared to controls (n = 14). Conclusions: RRD-induced rectal hypersensitivity seems to be reliable marker for IBS, and CRF may contribute to this response. FAPS patients may have hyposensitivity to non-noxious physiological distention, suggesting FAPS has different pathogenesis from IBS.