The hypersensitive gut: adequate approach or further confusion?

Central sensitization in patients with non-cardiac chest pain: a clinical experimental study

OBJECTIVE

Patients with non-cardiac chest pain (NNCP) suffer from unexplained and often intractable pain which can pose a major clinical problem. The aim of this study was to investigate nociceptive processing in NNCP patients and their response to experimentally acid-induced oesophageal hyperalgesia using a multimodal stimulation protocol.

MATERIAL AND METHODS

Ten highly selected patients with NCCP (mean age 43 years, 1 M) were compared with an age- and gender-matched group of 20 healthy subjects. After preconditioning, the distal oesophagus was painfully distended with a balloon using "impedance planimetry". This method assesses the luminal cross-sectional area of the oesophagus based on the electrical impedance of the fluid inside the balloon. The baseline distensions were done before and after pharmacological relaxation of the smooth muscle with 20 mg butylscopolamine. After baseline distensions, a series of up to 10 mechanical stimuli was performed (temporal summation). The stimulations were repeated after sensitization of the oesophagus induced by acid perfusion. The sensory intensities were assessed during the stimulations and the referred pain area was mapped.

RESULTS

At baseline distensions, no differences were seen between patients and controls before and after relaxation of the smooth muscles. The patients tolerated fewer repeated distensions than controls (4.8+/-0.5 versus 9.1+/-0.9; p=0.04) and had an increased size of the referred pain areas to the mechanical stimulations (32.9+/-6.2 versus 64.9+/-18.3 cm2; p=0.01). After sensitization with acid, the patients developed hyperalgesia (p<0.001), whereas no significant changes were seen in controls.

CONCLUSIONS

NCCP patients showed facilitated central pain mechanisms (temporal summation and visceral hyperalgesia after sensitization). This could be used in the diagnosis and understanding of the symptoms in these patients.

5-Hydroxytryptamine and functional bowel disorders

The possibility that 5-hydroxytryptamine (5-HT) acts as a key sensitising agent in the aetiology of irritable bowel syndrome (IBS) is reviewed. The strategic locations of 5-HT and its receptors are described, the most dominant being the 5-HT3 and 5-HT4 type. 5-HT, acting mostly at 5-HT3 or 5-HT3-like receptors, enhances the sensitivity of visceral neurones projecting between the gut and the central nervous systems. 5-HT, acting at 5-HT4 receptors promotes the sensitivity of enteric neurones that react to luminal stimuli. 5-HT4 and 5-HT3 receptors also mediate, respectively, sensitising and physiological actions of 5-HT on gastro-intestinal motor and secretory functions. This distribution implies that some 5-HT3 receptor antagonists might reduce certain symptoms of IBS, such as pain, by reducing the reactivity of the visceral afferent neurones linking the gut with the brain and spinal cord. However, such antagonists are not likely to find widespread clinical acceptance because they can also affect normal lower bowel function and promote constipation. 5-HT4 receptor antagonists, by contrast, reduce 5-HT-induced enteric nerve hypersensitivity without notably affecting the function of the normal bowel. Accordingly, these agents may reduce the symptoms of IBS directly, by reducing the incidence of defecation and diarrhoea and indirectly, by reducing both 'rebound' constipation and the post-prandial discomfort and pain associated with gastrointestinal hyper-reactivity.