The role of tension receptors in colonic mechanosensitivity in humans

Background: Perception of colonic distension, which is enhanced in a subset of patients with irritable bowel syndrome, requires activation of mechanoreceptors. In animal studies, distension activates both in series ("tension'') and in parallel ("elongation'') mechanoreceptors. During active contractions against a fixed volume balloon, tension receptors are activated without elongation of receptor activation. Aim: To evaluate the role of tension receptors in the perception of mechanical stimuli from the colon in healthy subjects. Methods: A 700 ml balloon connected to a barostat-manometer assembly was placed in the descending colon of 10 healthy subjects. After volume controlled distension ( 50 ml/2 minutes) to assess the first perception threshold, fixed volume subthreshold distension ( 122 ( 16) ml) was maintained for a 30 minute period before and after administration of neostigmine 0.5 mg intravenously. Mean intraballoon pressure, number, amplitude, and duration of contractions, and frequency of sensations were analysed. The period after neostigmine was divided into 10 second intervals and evaluated for the occurrence of contractions and onset of sensations. Fisher's exact test was applied to calculate the sensation-contraction association probability ( SAP) as (1.0-p) x 100%. Results: Neostigmine increased intraballoon pressure (p< 0.01), number of contractions (p< 0.01), and number of sensations ( p< 0.01) per minute in all subjects. In seven of 10 subjects a significant association (SAP >95%) was found between sensations and contractions. In the remaining subjects, contractions were not associated with sensations and had lower amplitude (p< 0.05) and duration ( p< 0.01) compared with contractions in the other seven subjects. Conclusion: In humans, tension receptors are involved in mediating colonic mechanosensitivity.