Evaluation of colonic sensory thresholds in IBS patients using a barostat. Definition of optimal conditions and comparison with healthy subjects

An Overview of the Effects of Tenapanor on Visceral Hypersensitivity in the Treatment of Irritable Bowel Syndrome with Constipation

Background

Patients with irritable bowel syndrome with constipation (IBS-C) experience persistent abdominal pain, a common symptom leading to greater healthcare utilization and reports of treatment non-response. Clinically significant improvements in abdominal pain were observed in clinical trials of tenapanor, a first-in-class inhibitor of sodium/hydrogen exchanger isoform 3 (NHE3), for the treatment of IBS-C in adults.

Aim

This narrative review reports the current knowledge about visceral hypersensitivity as a mechanism for abdominal pain in patients with IBS-C and explores the published evidence for hypothesized mechanisms by which tenapanor may reduce visceral hypersensitivity leading to the observed clinical response of decreased abdominal pain.

Findings

Abdominal pain is experienced through activation and signaling of nociceptive dorsal root ganglia that innervate the gut. These sensory afferent neurons may become hypersensitized through signaling of transient receptor potential cation channel subfamily V member 1 (TRPV1), resulting in reduced action potential thresholds. TRPV1 signaling is also a key component of the proinflammatory cascade involving mast cell responses to macromolecule exposure following permeation through the intestinal epithelium. Indirect evidence of this pathway is supported by observations of higher pain in association with increased intestinal permeability in patients with IBS. Tenapanor reduces intestinal sodium absorption, leading to increased water retention in the intestinal lumen, thereby improving gastrointestinal motility. In animal models of visceral hypersensitivity, tenapanor normalized visceromotor responses and normalized TRPV1-mediated nociceptive signaling.

Conclusion

By improving gastrointestinal motility, decreasing intestinal permeability and inflammation, and normalizing nociception through decreased TRPV1 signaling, tenapanor may reduce visceral hypersensitivity, leading to less abdominal pain in patients with IBS-C. Therapies that have demonstrated effects on visceral hypersensitivity may be the future direction for meaningful abdominal pain relief for patients with IBS-C.

Slow, deep breathing intervention improved symptoms and altered rectal sensitivity in patients with constipation-predominant irritable bowel syndrome

BACKGROUND AND AIM

Limited treatment options have been shown to alter the natural course of irritable bowel syndrome (IBS). Slow, deep breathing (SDB) is a common pain self-management intervention. This pilot study aimed to explore the impact of SDB on measures of autonomic and anorectal functions as well as patient-reported symptoms in constipation-predominant IBS (IBS-C).

METHODS

Eighty-five IBS-C patients were enrolled in this study and randomly assigned to the experimental group (Group A, n = 42) and the control group (Group B, n = 43). SDB was conducted at six breathing cycles per minute with an inhalation for 4 s and exhalation for 6 s at a ratio of 2:3 and repeated for 30 min during the intervention. All subjects underwent high-resolution anorectal manometry (HRAM) and completed the standardized IBS symptom severity system (IBS-SSS) questionnaire. Meanwhile, changes in stool consistency, weekly frequency of complete spontaneous bowel movements (CSBMs), and weekly frequency of spontaneous bowel movements (SBMs) were recorded. All IBS-C patients received electrocardiogram (ECG) recordings for heart rate variability (HRV) analysis at baseline, weeks 3, 6.

RESULTS

At baseline, no differences were found between Groups A and B. The IBS-SSS score and its five sub-scores of Group B patients were significantly higher at week 6 than those of Group A patients (all p < 0.001). Furthermore, compared with Group B patients, Group A patients had a significantly higher threshold volume for the first sensation (p < 0.001), desire to defecate (p = 0.017), and maximum tolerable volume (p = 0.018) at week 6 of the SDB treatment. We also noted significant improvements in stool consistency (p = 0.002), weekly SBM frequencies (p < 0.001), and weekly CSBM frequencies (p = 0.018) of Group A patients at week 6 when compared with Group B patients. Finally, the corrected high frequency (HF) of Group A patients was significantly higher than the HF of Group B patients at week 3 (p < 0.001) and at week 6 (p < 0.001). Likewise, patients in Group A had a significantly higher root mean square of the successive differences (RMSSD) than that of patients in Group B at week 3 (p < 0.001) and at week 6 (p < 0.001).

CONCLUSION

We found that a 6-week SDB intervention improved symptoms and altered rectal sensation in IBS-C patients. Moreover, SDB enhanced vagal activity. These findings suggest that the effect of SDB on IBS-C may be due to mechanisms involving autonomic responses.

Type of Rectal Barostat Protocol Affects Classification of Hypersensitivity and Prediction of Symptom Severity in Irritable Bowel Syndrome

Background/Aims

Visceral hypersensitivity is an important pathophysiologic mechanism in irritable bowel syndrome (IBS). We compared 2 barostat distension protocols and their ability to distinguish between IBS patients and healthy controls, identify subjects with rectal hypersensitivity, and their associations with gastrointestinal symptom severity.

Methods

We retrospectively reviewed all patients at our unit that had undergone barostat investigations 2002-2014. Protocol 1 (n = 369) used phasic isobaric distensions with stepwise increments in pressure and protocol 2 (n = 153) used pressure controlled ramp inflations. Both protocols terminated when subjects reported pain or maximum pressure was reached. Thresholds for first sensation, urgency, discomfort and pain were established. Age- and gender-matched controls were used for comparison. The gastrointestinal symptom rating scale-IBS, and the hospital anxiety and depression scale were used for symptom reports.

Results

A significantly higher proportion of patients was classified as having hypersensitivity in protocol 1 vs protocol 2 for all thresholds (P < 0.001). Patients with visceral hypersensitivity, defined based on rectal pain thresholds in protocol 1 had more severe gastrointestinal symptoms overall as well as anxiety, whereas these associations were weaker or in most cases absent when visceral hypersensitivity was defined based on rectal pain thresholds in protocol 2.

Conclusion

Our study indicates that a rectal barostat protocol using phasic isobaric distensions with stepwise pressure increments is more sensitive in IBS patients with respect to identifying subjects with rectal hypersensitivity and a link with IBS symptoms.

Randomized Trial of 2 Delayed-Release Formulations of Linaclotide in Patients With Irritable Bowel Syndrome With Constipation

INTRODUCTION

Immediate-release (IR) formulation of linaclotide 290 μg improves abdominal pain and constipation (APC) in patients with irritable bowel syndrome (IBS) with constipation. Delayed-release (DR) formulations were developed on the premise that targeting the ileum (delayed-release formulation 1 [DR1]) or ileocecal junction and cecum (MD-7246, formerly DR2) would modulate linaclotide's secretory effects while preserving pain relief effects.

METHODS

This phase 2b study randomized patients with IBS with constipation to placebo or 1 of 7 once-daily linaclotide doses (DR1 30, 100, or 300 μg; MD-7246 30, 100, or 300 μg; or IR 290 μg) for 12 weeks. Key efficacy endpoints were change from baseline in abdominal pain and complete spontaneous bowel movement frequency, and 6/12-week combined APC+1 responder rate.

RESULTS

Overall, 532 patients were randomized; mean age was 45.1 years, and most were women (83.3%) and White (64.7%). All linaclotide DR1 and MD-7246 groups experienced greater improvements in abdominal pain from baseline and vs placebo throughout treatment. Linaclotide DR1 and IR led to numerically greater improvements from baseline in complete spontaneous bowel movement frequency and higher APC+1 responder rates compared with placebo; MD-7246 results were similar to placebo. Diarrhea was the most common adverse event with DR1 and IR; rates were similar between MD-7246 and placebo.

DISCUSSION

Altering the site of drug delivery in the intestine might uncouple linaclotide's pain relief from secretory effects. Persistent, modest abdominal pain improvement with limited impact on bowel symptom parameters, as seen across MD-7246 doses, warrants further study of MD-7246 as a novel treatment for abdominal pain, regardless of IBS subtype.

GHSR-1 agonist sensitizes rat colonic intrinsic and extrinsic neurons to exendin-4: A role in the manifestation of postprandial gastrointestinal symptoms in irritable bowel syndrome?

BACKGROUND

Patients with irritable bowel syndrome (IBS) may experience postprandial symptom exacerbation. Nutrients stimulate intestinal release of glucagon-like peptide 1 (GLP-1), an incretin hormone with known gastrointestinal effects. However, prior to the postprandial rise in GLP-1, levels of the hunger hormone, ghrelin, peak. The aims of this study were to determine if ghrelin sensitizes colonic intrinsic and extrinsic neurons to the stimulatory actions of a GLP-1 receptor agonist, and if this differs in a rat model of IBS.

METHODS

Calcium imaging of enteric neurons was compared between Sprague Dawley and Wistar Kyoto rats. Colonic contractile activity and vagal nerve recordings were also compared between strains.

KEY RESULTS

Circulating GLP-1 concentrations differ between IBS subtypes. Mechanistically, we have provided evidence that calcium responses evoked by exendin-4, a GLP-1 receptor agonist, are potentiated by a ghrelin receptor (GHSR-1) agonist, in both submucosal and myenteric neurons. Although basal patterns of colonic contractility varied between Sprague Dawley and Wister Kyoto rats, the capacity of exendin-4 to alter smooth muscle function was modified by a GHSR-1 agonist in both strains. Gut-brain signaling via GLP-1-mediated activation of vagal afferents was also potentiated by the GHSR-1 agonist.

CONCLUSIONS & INFERENCES

These findings support a temporal interaction between ghrelin and GLP-1, where the preprandial peak in ghrelin may temporarily sensitize colonic intrinsic and extrinsic neurons to the neurostimulatory actions of GLP-1. While the sensitizing effects of the GHSR-1 agonist were identified in both rat strains, in the rat model of IBS, underlying contractile activity was aberrant.

Long-term treatment with plecanatide was safe and tolerable in patients with irritable bowel syndrome with constipation

Objective: This open-label, multi-center, fixed-dose study (NCT02706483) evaluated the long-term safety and tolerability of plecanatide for the treatment of adults with irritable bowel syndrome with constipation (IBS-C).Methods: Safety and tolerability of once-daily plecanatide 6 mg for up to 53 weeks was assessed in patients with IBS-C who either had been enrolled in one of the phase 3 studies or were study-naïve but met eligibility criteria of the double-blind studies. Safety was assessed by treatment-emergent adverse events (AEs). Patient-reported questionnaires assessed overall IBS symptoms, treatment satisfaction, and desire for treatment continuation. No dose adjustments or treatment interruptions were permitted during the study.Results: Of the 2272 patients enrolled, 1842 (81.1%) completed the study. AEs were experienced by 27.3%, and 4.3% discontinued due to an AE. Most AEs were mild or moderate (90.3%). The incidence of diarrhea, the most commonly reported AE, was low (6.7%), and declined in frequency over time. Diarrhea was the most common cause of AE-related withdrawals (2.7% of patients). At week 53 or end of treatment, 88.2% of patients reported "significant" or "moderate" relief, 72.4% were "very" or "quite" satisfied with treatment, and 76.6% were "very" or "quite" likely to continue treatment.Conclusions: Plecanatide 6 mg was safe and well tolerated in patients with IBS-C treated for up to 53 weeks, with an overall safety profile similar to the 12-week IBS-C studies. Patients reported high rates of relief and satisfaction with treatment, and interest in continuing therapy.Trial registration: ClinicalTrials.gov identifier: NCT02706483.

Paneth Cell Defects Induce Microbiota Dysbiosis in Mice and Promote Visceral Hypersensitivity

BACKGROUND & AIMS

Separation of newborn rats from their mothers induces visceral hypersensitivity and impaired epithelial secretory cell lineages when they are adults. Little is known about the mechanisms by which maternal separation causes visceral hypersensitivity or its relationship with defects in epithelial secretory cell lineages.

METHODS

We performed studies with C3H/HeN mice separated from their mothers as newborns and mice genetically engineered (Sox9^flox/flox-vil-cre on C57BL/6 background) to have deficiencies in Paneth cells. Paneth cell deficiency was assessed by lysozyme staining of ileum tissues and lysozyme activity in fecal samples. When mice were 50 days old, their abdominal response to colorectal distension was assessed by electromyography. Fecal samples were collected and microbiota were analyzed using Gut Low-Density Array quantitative polymerase chain reaction.

RESULTS

Mice with maternal separation developed visceral hypersensitivity and defects in Paneth cells, as reported from rats, compared with mice without maternal separation. Sox9^flox/flox-vil-Cre mice also had increased visceral hypersensitivity compared with control littermate Sox9^flox/flox mice. Fecal samples from mice with maternal separation and from Sox9^flox/flox-vil-cre mice had evidence for intestinal dysbiosis of the microbiota, characterized by expansion of Escherichia coli. Daily gavage of conventional C3H/HeN adult mice with 10⁹ commensal E coli induced visceral hypersensitivity. Conversely, daily oral administration of lysozyme prevented expansion of E coli during maternal separation and visceral hypersensitivity.

CONCLUSIONS

Mice with defects in Paneth cells (induced by maternal separation or genetically engineered) have intestinal expansion of E coli leading to visceral hypersensitivity. These findings provide evidence that Paneth cell function and intestinal dysbiosis are involved in visceral sensitivity.

The Place of Stress and Emotions in the Irritable Bowel Syndrome

Our emotional state can have many consequences on our somatic health and well-being. Negative emotions such as anxiety play a major role in gut functioning due to the bidirectional communications between gut and brain, namely, the brain-gut axis. The irritable bowel syndrome (IBS), characterized by an unusual visceral hypersensitivity, is the most common disorder encountered by gastroenterologists. Among the main symptoms, the presence of current or recurrent abdominal pain or discomfort associated with bloating and altered bowel habits characterizes this syndrome that could strongly alter the quality of life. This chapter will present the physiopathology of IBS and explain how stress influences gastrointestinal functions (permeability, motility, microbiota, sensitivity, secretion) and how it could be predominantly involved in IBS. This chapter will also describe the role of the autonomic nervous system and the hypothalamic-pituitary axis through vagal tone and cortisol homeostasis. An analysis is made about how emotions and feelings are involved in the disruption of homeostasis, and we will see to what extent the balance between vagal tone and cortisol may reflect dysfunctions of the brain-gut homeostasis. Finally, the interest of therapeutic treatments focused on stress reduction and vagal tone enforcement is discussed.

Recent advances in the diagnosis of irritable bowel syndrome

The symptom-based diagnosis of irritable bowel syndrome (IBS) has not been established in everyday clinical practice, and the diagnosis of this disorder remains one of exclusion. It has been demonstrated that the densities of duodenal chromogranin A, rectal peptide YY and somatostatin cells are good biomarkers for the diagnosis of sporadic IBS, and low-grade mucosal inflammation is a promising biomarker for the diagnosis of postinfectious IBS. Genetic markers are not useful as biomarkers for IBS since the potential risk genes have yet to be validated, and the intestinal microbiota cannot be used because of the lack of an association between a specific bacterial species and IBS. Furthermore, gastrointestinal dysmotility and visceral hypersensitivity tests produce results that are too nonconsistent and noncharacteristic to be used in the diagnosis of IBS. A combination of symptom-based assessment, exclusion of overlapping gastrointestinal diseases and positive biomarkers appears to be the best way to diagnose IBS.

Interaction between ingested nutrients and gut endocrine cells in patients with irritable bowel syndrome (review)

Several endocrine cell abnormalities have been reported in different segments of the gastrointestinal tract of patients with irritable bowel syndrome (IBS). These cells have specialized microvilli that project into the lumen; they function as sensors for the gut contents and respond to luminal stimuli (mostly ingested nutrients) by releasing hormones into the lamina propria, where they exert their effects via a paracrine/endocrine mode of action. Certain food items trigger the symptoms experienced by IBS patients, including those rich in fermentable oligo-, di- and monosaccharides, and polyols (FODMAPs). In this review, we present the argument that the effects of both FODMAPs and the proportional intake of proteins, fats and carbohydrates on IBS symptoms may be caused by an interaction with the gut endocrine cells. Since the gut hormones control and regulate gastrointestinal motility and sensation, this interaction may be responsible for abnormal gastrointestinal motility and the visceral hypersensitivity observed in these patients. There is no consistent evidence that IBS patients suffer from food allergy. The role of gluten intolerance in the development of IBS symptoms in these patients remains a matter of controversy. Individual guidance on food management, which includes restrictions in the intake of FODMAP-rich foods and testing diets with different proportions of proteins, fats and carbohydrates has been found to reduce the symptoms, improve the quality of life, and make the habitual diet of IBS patients more healthy.

Abdominal bloating: pathophysiology and treatment

Abdominal bloating is a very common and troublesome symptom of all ages, but it has not been fully understood to date. Bloating is usually associated with functional gastrointestinal disorders or organic diseases, but it may also appear alone. The pathophysiology of bloating remains ambiguous, although some evidences support the potential mechanisms, including gut hypersensitivity, impaired gas handling, altered gut microbiota, and abnormal abdominal-phrenic reflexes. Owing to the insufficient understanding of these mechanisms, the available therapeutic options are limited. However, medical treatment with some prokinetics, rifaximin, lubiprostone and linaclotide could be considered in the treatment of bloating. In addition, dietary intervention is important in relieving symptom in patients with bloating.

Sensations of gas and pain and their relationship with compliance during distension in human colon

BACKGROUND

Colonic mechanosensory afferents 'in parallel' to circular muscle activate prevertebral ganglion reflexes; 'in series', afferents convey visceral sensation to the central nervous system; and pain receptors are activated with muscle distension. Our aim was to analyze the relationships of gas and pain sensations during graded distensions, and the association of sensations with colonic compliance in conscious humans.

METHODS

The data were acquired in a prior study performed on 60 healthy volunteers (aged 18-75 years) under baseline conditions. Colonic compliance was measured in response to 4 mmHg stepwise balloon distensions to estimate pressure at half-maximum volume (Pr(50%)). Sensation ratings for gas and pain were averaged over distensions at 16, 24, 30 and 36 mmHg above baseline operating pressure. Associations between mean gas and pain ratings, and colonic compliance were assessed with Pearson correlations.

KEY RESULTS

Gas and pain sensations were significantly correlated at all levels of distension (all P < 0.001). Significant inverse correlations between Pr(50%) and sensations of gas and pain were observed, suggesting that lower compliance was associated with lower sensations. Up to 25% of the variance in sensation may be attributed to colonic compliance.

CONCLUSIONS & INFERENCES

These data are consistent with the hypothesis that, if circumferential colonic receptors are stimulated by distension to mediate gas and pain in humans, they are, at least partly, arranged 'in parallel' to the muscle layer.

Plasma hormones facilitated the hypermotility of the colon in a chronic stress rat model

Objective

To study the relationship between brain-gut peptides, gastrointestinal hormones and altered motility in a rat model of repetitive water avoidance stress (WAS), which mimics the irritable bowel syndrome (IBS).

Methods

Male Wistar rats were submitted daily to 1-h of water avoidance stress (WAS) or sham WAS (SWAS) for 10 consecutive days. Plasma hormones were determined using Enzyme Immunoassay Kits. Proximal colonic smooth muscle (PCSM) contractions were studied in an organ bath system. PCSM cells were isolated by enzymatic digestion and IKv and IBKca were recorded by the patch-clamp technique.

Results

The number of fecal pellets during 1 h of acute restraint stress and the plasma hormones levels of substance P (SP), thyrotropin-releasing hormone (TRH), motilin (MTL), and cholecystokinin (CCK) in WAS rats were significantly increased compared with SWAS rats, whereas vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and corticotropin releasing hormone (CRH) in WAS rats were not significantly changed and peptide YY (PYY) in WAS rats was significantly decreased. Likewise, the amplitudes of spontaneous contractions of PCSM in WAS rats were significantly increased comparing with SWAS rats. The plasma of WAS rats (100 µl) decreased the amplitude of spontaneous contractions of controls. The IKv and IBKCa of PCSMs were significantly decreased in WAS rats compared with SWAS rats and the plasma of WAS rats (100 µl) increased the amplitude of IKv and IBKCa in normal rats.

Conclusion

These results suggest that WAS leads to changes of plasma hormones levels and to disordered myogenic colonic motility in the short term, but that the colon rapidly establishes a new equilibrium to maintain the normal baseline functioning.

Role of neuronal nitric oxide synthase in colonic distension-induced hyperalgesia in distal colon of neonatal maternal separated male rats

BACKGROUND

Nitric oxide (NO) is implicated in the pathogenesis of irritable bowel syndrome (IBS) but the underlying mechanism is unclear. Thus, the aim of the present study is to examine the role of NO synthase (NOS) expression in the distal colon of neonatal maternal separation (NMS) model rats employed in IBS studies.

METHODS

Male neonates of Sprague-Dawley rats were randomly assigned into NMS and normal control (N) groups. Rats of NMS group were subjected to 3 h daily maternal separation on postnatal day 2-21. Rats were administrated non-selective NOS inhibitor l-NAME (100 mg kg(-1) ), selective neuronal NOS (nNOS) inhibitor 7-NINA (10mgkg(-1) ), selective inducible NOS (iNOS) inhibitor, endothelial NOS (eNOS) inhibitor (10mgkg(-1) ) or Vehicle (Veh; distilled water) intraperitoneally 1h prior to the experiment for the test and control groups, respectively.

KEY RESULTS

The amount of NO was significantly higher in the NMS Veh rats compared with unseparated N rats. Western-blotting and real-time quantitative PCR studies showed that protein and mRNA expression of nNOS were higher in the NMS group than that in the N rats; whereas no significant change in iNOS and eNOS was found in either groups. Neonatal maternal separation Veh rats showed low pain threshold and increased electromyogram (EMG) activity in response to colonic distension stimuli. l-NAME and 7-Nitroindazole monosodium salt (7-NINA) increased pain threshold pressure and attenuated EMG activity in the NMS rats. In addition, l-NAME and 7-NINA substantially reduced oxidative marker malondialdehyde level in NMS rats.

CONCLUSIONS & INFERENCES

Neonatal maternal separation increased the NO generation by nNOS upregulation that interact with reactive oxygen species contributing to the visceral hypersensitivity in IBS.

Irritable pouch syndrome is characterized by visceral hypersensitivity

BACKGROUND

Irritable pouch syndrome (IPS) is a functional disorder in patients with ileal pouch-anal anastomosis (IPAA), which presents with symptoms in the absence of structural abnormalities of the pouch. Thus, it resembles other functional disorders, such as irritable bowel syndrome characterized by visceral hypersensitivity in the presence of normal rectal biomechanics. The aim was to assess pouch biomechanics and perception of balloon distension in different groups of subjects with IPAA and to correlate the findings with clinical features.

METHODS

Pouch tone, compliance, and sensation to balloon distension were measured in 18 patients with IPS, 11 patients with active pouch inflammation (pouchitis or Crohn's disease of the pouch), and 12 asymptomatic subjects with normal pouches. All patients were recruited from a subspecialty Pouchitis Clinic.

RESULTS

Scores of sensation of gas, urge to defecate, and pain measured by visual analog scales at various distension pressures were significantly higher in IPS than pouchitis and normal pouch patients. Pouch tone was comparable among the groups and compliance was reduced in the pouchitis group. The visual analog scale showed a trend of correlation with the Pouchitis Disease Activity Index symptom scores in IPS.

CONCLUSIONS

IPS, like other gut functional disorders, is characterized by visceral hypersensitivity, with normal pouch biomechanics.

Asian motility studies in irritable bowel syndrome

Altered motility remains one of the important pathophysiologic factors in patients with irritable bowel syndrome (IBS) who commonly complain of abdominal pain and stool changes such as diarrhea and constipation. The prevalence of IBS has increased among Asian populations these days. Gastrointestinal (GI) physiology may vary between Asian and Western populations because of differences in diets, socio-cultural backgrounds, and genetic factors. The characteristics and differences of GI dysmotility in Asian IBS patients were reviewed. MEDLINE search work was performed including following terms, 'IBS,' 'motility,' 'transit time,' 'esophageal motility,' 'gastric motility,' 'small intestinal motility,' 'colonic motility,' 'anorectal function,' and 'gallbladder motility' and over 100 articles were categorized under 'esophagus,' 'stomach,' 'small intestine,' 'colon,' 'anorectum,' 'gallbladder,' 'transit,' 'motor pattern,' and 'effect of stressors.' Delayed gastric emptying, slow tansit in constipation predominant IBS patients, rapid transit in diarrhea predominant IBS patients, accelerated motility responses to various stressors such as meals, mental stress, or corticotrophin releasing hormones, and altered rectal compliance and altered rectal accomodation were reported in many Asian studies regarding IBS. Many conflicting results were found among these studies and there are still controversies to conclude these as unique features of Asian IBS patients. Multinational and multicenter studies are needed to be performed vigorously in order to elaborate characteristics as well as differences of altered motililty in Asian patients with IBS.

Differential roles of stretch-sensitive pelvic nerve afferents innervating mouse distal colon and rectum

Information about colorectal distension (i.e., colorectal dilation by increased intraluminal pressure) is primarily encoded by stretch-sensitive colorectal afferents in the pelvic nerve (PN). Despite anatomic differences between rectum and distal colon, little is known about the functional roles of colonic vs. rectal afferents in the PN pathway or the quantitative nature of mechanosensory encoding. We utilized an in vitro mouse colorectum-PN preparation to investigate pressure-encoding characteristics of colorectal afferents. The colorectum with PN attached was dissected, opened longitudinally, and pinned flat in a Sylgard-lined chamber. Action potentials of afferent fibers evoked by circumferential stretch (servo-controlled force actuator) were recorded from the PN. Stretch-sensitive fibers were categorized into the following four groups: colonic muscular, colonic muscular/mucosal, rectal muscular, and rectal muscular/mucosal. Seventy-nine stretch-sensitive PN afferents evenly distributed into the above four groups were studied. Rectal muscular afferents had significantly greater stretch-responses than the other three groups. Virtually all rectal afferents (98%) had low thresholds for response and encoded stimulus intensity into the noxious range without obvious saturation. Most colonic afferents (72%) also had low thresholds (<14 mmHg), but a significant proportion (28%) had high thresholds (>18 mmHg) for response. These high-threshold colonic afferents were sensitized to stretch by inflammatory soup; response threshold was significantly reduced (from 23 to 12 mmHg), and response magnitude significantly increased. These results suggest that the encoding of mechanosensory information differs between colonic and rectal stretch-sensitive PN afferents. Rectal afferents have a wide response range to stretch, whereas high-threshold colonic afferents likely contribute to visceral nociception.

Peripheral factors in the pathophysiology of irritable bowel syndrome

The pathophysiology of IBS is complex and still incompletely known. Both central and peripheral factors are thought to contribute to the symptoms of IBS, including psychosocial factors, abnormal GI motility and secretion, and visceral hypersensitivity. In this review the involvement of peripheral factors in the pathophysiology in IBS is reviewed. Altered GI motility is commonly found in this patient group, even though a specific motor pattern has been hard to find. Colonic transit has been found to be of relevance for the bowel habit of the patient. Abnormal gas handling within the gut is also commonly seen, and seems to be one, but not the only factor responsive for bloating. There is also limited evidence supporting the presence of abnormal GI secretion in IBS, but its relevance for symptoms remains unclear. Visceral hypersensitivity is currently considered to be one of the most important pathophysiological factors in IBS. It can be modulated by several external and internal factors and recent studies support an association between colorectal sensitivity and the symptoms reported by the patients, especially pain.

Influence of naloxone on rectal sensorimotor function in health

Abnormal rectal motor physiology and visceral hypersensitivity are implicated in the pathogenesis of irritable bowel syndrome. Endogenous opioids are involved in both the regulation of gut motility and the processing of sensory information. Our aim was to study the effect of suppression of endogenous opioid function by naloxone on rectal sensorimotor function in health. Eighteen healthy subjects participated in a rectal barostat study. Sensorimotor function was evaluated during two consecutive stepwise distensions separated by 30 min of basal tone recording, and with perception scoring on a 0-6 graded scale. Naloxone was administered, after 15 min of basal tone measurements, as an intravenous bolus (0.4 mg), followed by continuous infusion (20 microg kg(-1) h(-1)) in a placebo-controlled, single-blinded and randomized fashion. Naloxone did not alter rectal sensitivity. Comparison of visual analogue scale scores between naloxone and saline did not reveal altered intensities of pain or discomfort. Compared to the baseline distension, a significant adaptive increase in compliance occurred during the second distension after saline (7.8 +/- 0.7 vs 11.0 +/- 0.6 mL mmHg(-1), P = 0.0016). This dynamic change in rectal compliance did not occur after naloxone administration (8.8 +/- 0.7 vs 10.1 +/- 0.8 mL mmHg(-1), ns). Low intensity tonic distension induced a rectal adaptive relaxation, which was absent after naloxone. Naloxone does not alter rectal sensitivity but abolishes rectal adaptation in response to repeated balloon distention. These observations suggest that the endogenous opioid system is involved in control of rectal tone rather than rectal sensitivity.

Fecal proteases from diarrheic-IBS and ulcerative colitis patients exert opposite effect on visceral sensitivity in mice

Elevated colonic luminal serine-protease (Ser-P) activity of diarrhea-predominant IBS (IBS-D) patients evokes a proteinase-activated receptor (PAR)-2-mediated colonic hypersensitivity in mice. Despite similarly elevated Ser-P levels in feces, patients with IBD exhibit visceral hypo- or normosensitivity to rectal distension, as opposed to IBS-D. To explain these discrepancies we studied the effect of colonic infusion of fecal supernatants from ulcerative colitis (UC) patients to colorectal mechanical sensitivity of mice and explored the involvement of PAR-4 and its activator Cathepsin-G (Cat-G). Fecal protease activities were assayed in healthy subjects, IBS-D and UC patients in presence or not of antiproteases or Cat-G inhibitor. Following intracolonic infusion of fecal supernatants from healthy subjects, IBS-D and UC patients or PAR-4 activating peptide (PAR-4-AP) or Cat-G, EMG response to colorectal balloon distension was recorded in mice. This nociceptive response was also determined after treatment with pepducin (PAR-4 antagonist) on UC supernatant or after a preincubation with antiproteases or Cat-G inhibitor. In contrast to IBS-D supernatant, UC supernatant promoted colonic hyposensitivity to distension, an effect mimicked by PAR-4-AP or Cat-G. UC supernatant-induced hypoalgesia was inhibited by a cocktail of antiproteases. However, blockade of PAR-4 or Cat-G inhibition resulted in colonic hypersensitivity similar to that observed after IBS-D supernatant infusion. Despite similarly elevated Ser-P activities, IBS-D and UC fecal supernatant display visceral pro- and antinociceptive effects in mice, respectively. Visceral hyposensitivity induced by fecal supernatant from UC patients results from PAR-4 activation by cathepsin-G, counterbalancing the pronociceptive effect of simultaneous PAR-2 activation.

Novel techniques to study visceral hypersensitivity in irritable bowel syndrome

Visceral hypersensitivity has emerged as a key hypothesis in explaining the painful symptoms of irritable bowel syndrome (IBS), and it has been proposed as a "biologic marker" for the condition. Visceral hypersensitivity can be influenced by peripheral and central mechanisms affecting pain perception. The optimal method for its assessment in humans has not been determined. Current techniques include stimulation via the computerized barostat and electrical stimulation, response measures including the lower limb reflex, and brain imaging modalities such as functional MRI and positron emission tomography. It has been shown that IBS patients have decreased sensory thresholds to colonic and rectal balloon distention by barostat. Studies using electrical stimulation and the RIII lower limb reflex have further confirmed enhanced visceral perception in IBS. Evidence from more recent neuro-imaging studies suggests that IBS patients have abnormal activation of brain circuits involved in emotional and cognitive modulation of sensory information, resulting in ineffective pain modulation; these circuits may have a pathophysiologic role in enhancing visceral perception. There are few effective pharmacologic treatments that relieve IBS symptoms, and improved understanding of brain-gut interactions and factors relating to enhanced visceral perception may guide us in developing more efficacious treatments.

Enterochromaffin cell hyperplasia in irritable pouch syndrome

BACKGROUND

Irritable pouch syndrome (IPS) is a functional disease in patients with ileal pouch-anal anastomosis following colectomy for ulcerative colitis (UC). The pathophysiology of IPS is characterized by the presence of visceral hypersensitivity, similar to that seen in irritable bowel syndrome. However, the exact etiology and pathogenesis of IPS are not known. We hypothesized that serotonin-containing enteroendocrine cells or enterochromaffin (EC) cell hyperplasia and alterations in the mucosal immune cells may contribute to the patients' symptoms. The aim of the study was to assess EC cell hyperplasia and alterations in the mucosal immune cells in IPS.

METHODS

The Pouchitis Disease Activity Index (PDAI) was used to quantify symptoms and mucosal inflammation in 36 patients with IPS and 25 patients with normal pouches. The histology and immunohistochemistry of pouch mucosal biopsies were assessed by a blinded gastrointestinal pathologist for intraepithelial lymphocytes (IEL), CD3+ T cells, CD25- (interleukin [IL]-2 receptor), tryptase- (mast cells), and serotonin-expressing cells. The numbers of IEL and immune-stained cells were compared between the two groups.

RESULTS

Both groups were compatible demographically in terms of age, gender, duration of UC, stage, indication, and duration of the pouch surgery. There were no differences in the number of IEL, CD3+ T cells, CD25+ cells, and mast cells between the IPS and normal control groups. However, there were a significantly larger number of EC cells in the IPS group than that in the control group (54.8 +/- 24.9 vs 36.7 +/- 17.5 per 4 200x epithelial cells, P < 0.005). The number of EC cells appeared to be correlated with the symptom score (r = 0.276, P= 0.032). There were no significant correlations between the PDAI endoscopy and histology scores and the number of EC cells or between the PDAI scores and the number of IEL or other immune-stained cells.

CONCLUSIONS

A greater number of EC cells were found in the IPS group than the normal pouch group, and the number of EC cells appeared to be correlated with the clinical symptoms of IPS. EC cell hyperplasia may be a contributing mechanism of visceral hypersensitivity and symptoms in IPS.

Relationship between rectal sensitivity, symptoms intensity and quality of life in patients with irritable bowel syndrome

BACKGROUND

Relationships between pain threshold during rectal distension and both symptoms intensity and alteration in quality of life (QoL) in irritable bowel syndrome (IBS) patients have been poorly evaluated.

AIM

To evaluate relationships between rectal sensitivity, IBS symptom intensity and QoL in a multicentre prospective study.

METHODS

Rectal threshold for moderate pain was measured during rectal distension in IBS patients (Rome II), while IBS symptoms intensity was assessed by a validated questionnaire and QoL by the Functional Digestive Disorder Quality of Life questionnaire.

RESULTS

Sixty-eight patients (44.2 +/- 12.7 years, 48 women) were included. The mean rectal distending volume for moderate pain was 127 +/- 35 mL while 45 patients (66%) had rectal hypersensitivity (pain threshold <140 mL). Rectal threshold was not significantly related either to overall IBS intensity score (r = -0.66, P = 0.62) or to its different components, or to FDDQL score (r = 0.30, P = 0.14). Among FDDQL domains, only anxiety (r = 0.30, P = 0.01) and coping (r = 0.31, P = 0.009) were significantly related with pain threshold.

CONCLUSIONS

In this study, two-thirds of IBS patients exhibited rectal hypersensitivity. No significant correlation was found between rectal threshold and either symptom intensity or alteration in QoL.

Analysis of rectal dynamic and static compliances in patients with irritable bowel syndrome

AIMS

Our aim was to investigate whether the dynamic and static compliances differ between patients with irritable bowel syndrome (IBS) and normal subjects.

MATERIALS AND METHODS

Fifty-five IBS patients (age range 20-65 years, mean age 39.0 years, 28 women and 27 men; 36 diarrhea-predominant IBS (IBS-D) patients and 19 constipation-predominant IBS (IBS-C) patients) with symptoms that fulfilled the Rome-II criteria and 21 healthy controls (age range 25-58 years, mean age 37.8 years; 11 women and ten men) were recruited. The anorectal functions, including dynamic compliance, were evaluated via barostat tests. A power exponential model was used for the evaluation of static compliance.

RESULTS

There was no significant difference in dynamic compliance between the normal subjects and the IBS patients (10.3+/-3.1 and 8.9+/-2.9 mmHg, respectively, P>0.05). However, even though no significant difference was detected in the overall shape of the curve (beta; P>0.05), there were significant differences in the kappa and P (half) between the normal subjects and the IBS patients (P<0.05), respectively. When we compared the dynamic and static compliances between the IBS-C and IBS-D patients, there were no significant differences found (P>0.05).

CONCLUSIONS

An exponential model provided good fit to the actual data, and there were significant differences in static compliance between the normal subjects and the IBS patients. This result can reveal the altered biomechanical properties of the gut wall in IBS patients.

Influence of the pattern of jejunal distension on mesenteric afferent sensitivity in the anaesthetized rat

Vagal, spinal and intestino-fugal fibres all potentially transmit mechanosensory afferent information from the gastrointestinal tract. We aimed to characterize the relative mechanosensitivity of these three different afferent populations supplying the rat jejunum. Afferent nerve discharge was recorded from pentobarbitone-anaesthetized rats during different distension protocols. Saline ramp distension (1 mL min(-1)) and barostat ramp distension (2 mmHg 4 s(-1)) each evoked biphasic responses but with the latter significantly attenuated especially at low distending pressures. Barostat controlled phasic distensions (10-50 mmHg, 25 s) evoked an afferent response with a peak at the onset of distension adapting to a plateau level that was maintained and comparable to the barostat ramp responses at the corresponding pressures. Chronic subdiaphragmatic vagotomy significantly attenuated the low pressure component of the response to balloon ramp distension and both peak and plateau responses to phasic distension. Single unit analysis showed an absence of low threshold afferent activity after vagotomy while the response to fibres with wide-dynamic range and high threshold sensitivity were preserved hexamethonium had no effect on the responses to either ramp or phasic distension. These findings suggest that the nature of the distension stimulus is critical in determining the pattern of response observed from the various subpopulations of afferents supplying the bowel wall.

Review article: abdominal bloating and distension in functional gastrointestinal disorders--epidemiology and exploration of possible mechanisms

BACKGROUND

A sensation of abdominal bloating, sometimes accompanied by an increase in girth (distension), is one of the most common and most intrusive features of functional bowel disorders.

AIM

To conduct a systematic, evidence-based review of the epidemiology and pathophysiology of abdominal bloating and its relationship to distension.

METHODS

The terms bloating, distension, functional bowel, irritable bowel syndrome, constipation and diarrhoea were searched on MEDLINE up to 2006. References from selected articles and relevant abstracts were also included.

RESULTS

Approximately 50% of irritable bowel syndrome patients with bloating also experience an increase in abdominal girth and this is more pronounced with constipation than diarrhoea. Bloating appears to be more frequently associated with visceral hypersensitivity, whereas distension is more often related to hyposensitivity and delayed transit. Although there is little evidence for excessive gas as a cause of bloating, gas infusion studies suggest that handling of gas may be impaired in irritable bowel syndrome and there may also be abnormal relaxation of the anterior abdominal musculature in these patients.

CONCLUSIONS

There is unlikely to be a single cause for bloating and distension, which probably have different, but overlapping, pathophysiological mechanisms. Relieving constipation might help distension, but the treatment of bloating may need more complex approaches involving sensory modulation.

A new intelligent distension system for hollow organs

Controlled distension of hollow organs is an accepted technique for generating reproducible visceral stimuli. We have constructed a new, flexible and intelligent distension system in which discomfort, pain and autonomic responses are recorded online. These responses can be fed back into the system in a regulatory loop and be used to shape the distension paradigm. Consequently, it is possible to take all subjects to a state of equal, although subjective, level of discomfort or pain, even though pressure, tension and volume might be totally different. By using a variable airflow, this new distension system can be effectively used in all kinds of paradigms, e.g. phasic, tonic, or ramp distensions or customized combinations of them. The system can be used to control pressure, volume or tension. A refinement of the system is that it is possible to automatically change the controlled entity during a distension, e.g. from an isobaric ramp directly into an isovolumetric tonic phase. Furthermore, the distension device allows double distensions with independent distension paradigms.

Somatic referral of visceral sensations and rectal sensory threshold for pain in children with functional gastrointestinal disorders

OBJECTIVE

To test the hypothesis that abdominal pain related to functional gastrointestinal disorders is associated with visceral hypersensitivity and abnormal perception of visceral sensations.

STUDY DESIGN

We examined 35 children (10-17.6 years old) fulfilling the Rome II criteria with irritable bowel syndrome (IBS; n = 21), functional abdominal pain (FAP; n = 8) or functional dyspepsia (FD; n = 6) compared with 10 control subjects (10.2-16.1 years). All underwent a rectal barostat examination. Painful sensations were reported on a human body diagram. The projections of sensations induced by rectal distension, the rectal sensory threshold for pain (RSTP) and the diagnostic value of RSTP measurements were measured.

RESULTS

Rectal distension induced sensations that projected to the S3 dermatome in the control subjects and FD and to aberrant sites in children with IBS and FAP. The RSTP was decreased in children with IBS and FAP compared with control subjects (P <.002) and was not different in children with FD compared with control subjects. At 30.8 mm Hg, the 5th percentile for the control subjects, the RSTP had a sensitivity rate of 89% and a specificity rate of 83% for IBS and FAP diagnosis.

CONCLUSION

Children with IBS and FAP are characterized by the association of rectal hypersensitivity and abnormal pain referral after rectal distension.

Colonic response to food in constipation

OBJECTIVES

Colonic response to food is possibly abnormal in constipation.

METHODS

The colonic response to food was evaluated in 323 patients and 60 healthy subjects by following the movements of radiopaque markers after ingestion of a standard 1,000-cal test meal. Constipated patients were divided into four groups: one with a normal, and three with a delayed colorectal transit time. When the delay was found mainly in the ascending colon, the group was labeled as suffering from "colonic inertia". In "hindgut dysfunction", the delay was predominantly found in the descending colon, whereas the term "outlet obstruction" was reserved for constipated patients whose major site of delay was the rectosigmoid area. Colonic response to food was quantified by evaluating the variation of markers in a given abdominal region and the evolution of the geometric center on the entire plain film of the abdomen.

RESULTS

Emptying of the caecum-ascending colon and filling of the rectosigmoid area characterize the colonic response to food in healthy subjects. Constipated patients also filled the rectosigmoid, but different patterns were found in the colon. In constipated patients with transit in the normal range, there was a frequent (41%) absence of colonic response to food as compared to controls (13%) and constipated patients with delayed transit (p<0.0001). The response to food of patients with colonic inertia was similar to that of healthy subjects in terms of distal progression, but less marked. The hindgut dysfunction group emptied the entire left colon but failed to empty the caecum and ascending colon. In the outlet obstruction group, there was no distal progress of the geometric center after meal.

CONCLUSIONS

Abnormal colonic response to food is frequently found in constipated patients, with different patterns according to the type of constipation.

Sensitivity disturbances in patients with irritable bowel syndrome and fibromyalgia

BACKGROUND

Although visceral hypersensitivity is a common feature among patients with irritable bowel syndrome (IBS), studies on somatic sensitivity have given controversial results.

AIM

To assess visceral sensitivity in response to isotonic rectal distensions and somatic sensitivity at different layers of the body wall (skin, subcutis, and muscle) in patients with IBS and fibromyalgia (FM), within and outside the area of abdominal pain referral.

MATERIALS AND METHODS

We studied 10 patients with IBS, 5 patients with FM, 9 patients with IBS+FM, and 9 healthy controls. Rectal distensions were performed by increasing tension at 4 g steps up to 64 g or discomfort. Pain thresholds to electrical stimulation were measured within and outside the areas of abdominal pain referral.

RESULTS

Patients with IBS and IBS+FM demonstrated rectal hypersensitivity in comparison to controls. The threshold of discomfort was 44 +/- 5 g in IBS and 36 +/- 5 in IBS+FM patients, while patients with FM and healthy controls tolerated all distensions without discomfort. In the areas of pain referral, pain thresholds of all three tissues of the body wall were lower than normal in all patients groups (p < 0.001). In control areas, the pain thresholds were normal in skin, and lower than normal in subcutis and muscle in IBS (p < 0.001). FM and IBS+FM demonstrated somatic hypersensitivity at all sites (p < 0.001 vs healthy).

CONCLUSION

Our observations seem to indicate that, although sharing a common hypersensitivity background, multiple mechanisms may modulate perceptual somatic and visceral responses in patients with IBS and FM.

Barostat testing in children with functional gastrointestinal disorders

Children and adolescents with chronic defecation disorders and chronic abdominal pain without obvious organic etiology form a challenging group of patients for pediatric health-care professionals. The pathophysiologic mechanisms underlying such functional gastroenterology disorders are poorly understood. Research studies on the use of the barostat have been aimed to increase our knowledge in this area. Barostat testing allows defining visceral hyper- or hyposensitivity, contractility, and compliance of the gut. This review focuses on rectal barostat studies performed in children with abdominal pain, constipation, and fecal incontinence.

Review article: uncomplicated diverticular disease of the colon

Diverticular disease of the colon is the fifth most important gastrointestinal disease in terms of direct and indirect health care costs in western countries. Uncomplicated diverticular disease is defined as the presence of diverticula in the absence of complications such as perforation, fistula, obstruction and/or bleeding. The distribution of diverticula along the colon varies worldwide being almost always left-sided and directly related to age in western countries and right-sided where diet is rich in fibre. The pathophysiology of diverticular disease is complex and relates to abnormal colonic motility, changes in the colonic wall, chronic mucosal low-grade inflammation, imbalance in colonic microflora and visceral hypersensitivity. Moreover, there can be genetic factors involved in the development of colonic diverticula. The use of non-absorbable antibiotics is the mainstay of therapy in patients with mild to moderate symptoms, and the effect of fibre-supplementation alone does not appear to be significantly different from placebo, although no definite data are available. More recently, alternative treatments have been reported. Mesalazine acts as a local mucosal immunomodulator and has been shown to improve symptoms and prevent recurrence of diverticulitis. In addition, probiotics have also been shown to be beneficial by re-establishing a normal gut microflora. In this study, the current literature on uncomplicated diverticular disease of the colon is reviewed.

Functional findings in irritable bowel syndrome

The pathophysiology of IBS is complex and still incompletely known. Both central and peripheral factors, including psychosocial factors, abnormal GI motility and secretion, and visceral hypersensitivity, are thought to contribute to the symptoms of IBS. Several studies have demonstrated altered GI motor function in IBS patients and the pattern differs between IBS subgroups based on the predominant bowel pattern. Few studies have so far addressed GI secretion in IBS, but there are some evidence supporting altered secretion in the small intestine of IBS patients. Visceral hypersensitivity is currently considered to be perhaps the most important pathophysiological factor in IBS. Importantly, several external and internal factors can modulate visceral sensitivity, as well as GI motility, and enhanced responsiveness within the GI tract to for instance stress and nutrients has been demonstrated in IBS patients. Today IBS is viewed upon as a disorder of dysregulation of the so-called brain-gut axis, involving abnormal function in the enteric, autonomic and/or central nervous systems, with peripheral alterations probably dominating in some patients and disturbed central processing of signals from the periphery in others.

Distension technique influences the relationship between colonic and rectal hypersensitivity in irritable bowel syndrome

In irritable bowel syndrome (IBS), it remains unclear whether rectal hypersensitivity is a 'marker' of colonic hypersensitivity. Our aim was to examine the relation between colonic and rectal sensitivity in IBS patients, comprising phasic and ramp distension techniques. Twenty IBS patients and 12 healthy subjects (N) underwent stepwise ramp and random phasic barostat distensions in the colon and rectum in random order. The sensory threshold pressure (ramp distension) and the visual analogue scale score (VAS, phasic distension), for pain and non-pain, were recorded. Colonic thresholds were lower, and VAS scores were generally higher, for pain and non-pain sensitivities in IBS compared to N. Rectal thresholds were lower, and VAS scores were higher, for pain but not for non-pain, in IBS compared to N. In IBS, for phasic distension, there was good correlation between the colon and rectum for non-pain (e.g. at 16 mmHg, r=0.59, P=0.006) and pain (r=0.60, P=0.006) sensitivities. In contrast, there was no significant correlation between the colon and rectum for ramp distension. In conclusion, colonic and rectal sensitivity in IBS are correlated in response to phasic but not ramp barostat distensions. The rectum serves as a legitimate 'window' for evaluating colonic hypersensitivity in IBS, provided that phasic distensions are employed.

Visceral hypersensitivity in irritable bowel syndrome: a summary review

We examined published reports from 1970 to the present to evaluate the theory that abnormal visceral sensitivity characterizes the irritable bowel syndrome. Evidence to support claims that abnormal visceral sensitivity defines the irritable bowel syndrome falls short because of cognitive deficits in gastrointestinal neurobiology, limitations in experimental design and execution, and the interpretation of results.

Rectal afferent hypersensitivity and compliance in irritable bowel syndrome: differences between diarrhoea-predominant and constipation-predominant subgroups

OBJECTIVES

To evaluate the differences in rectal compliance and sensory thresholds for the urge to defecate and discomfort between irritable bowel syndrome (IBS) subgroups and controls, and to correlate these parameters with rectal symptoms.

METHODS

A total of 38 IBS patients [Rome II criteria; 19 diarrhoea-predominant IBS (D-IBS), 16 constipation-predominant IBS (C-IBS), three with alternating diarrhoea and constipation IBS (Alt-IBS)] and 10 controls were studied. A barostat was used to measure rectal compliance and sensory thresholds, in the 'unprepared' rectum. The thresholds for the urge to defecate and discomfort were determined using phasic rectal balloon distension in a double random staircase sequence.

RESULTS

D-IBS had significantly lower rectal compliance and threshold for the urge to defecate compared with controls [4 ml/mmHg interquartile range (IQR) 3.99 versus 8.4 ml/mmHg IQR 5.69; P=0.001; 8 mmHg IQR 6 versus 20 mmHg IQR 4; P=0.003]. D-IBS also had significantly lower rectal compliance and threshold for the urge to defecate compared with the C-IBS group (5.8 ml/mmHg IQR 4.61; P=0.027; 16 mmHg IQR 12; P=0.003). The volume at the threshold for discomfort was significantly lower in D-IBS compared with controls (163 ml IQR 99.5 versus 212 ml IQR 147.25; P=0.016). The severity of abdominal pain and rectal symptoms showed a significantly negative correlation with rectal sensory thresholds.

CONCLUSION

This study shows that the sensory threshold for the urge to defecate and rectal compliance is significantly lower in D-IBS compared with C-IBS and controls. The consequent inability to tolerate rectal faecal loading may account for the symptoms of the passage of frequent, small-volume stools in D-IBS patients.

Influence of acute serotonin reuptake inhibition on colonic sensorimotor function in man

BACKGROUND

It is unclear whether decreased serotonin transporter function contributes to sensorimotor abnormalities in irritable bowel syndrome.

AIM

To study the influence of acute serotonin transporter inhibition on colonic sensorimotor function in man.

METHODS

Ten healthy subjects (five men, aged 20-29 years) underwent a combined manometry/barostat study of the descending colon on two occasions. Stepwise distentions by 2 mmHg increments were performed until discomfort. Subsequently, placebo or citalopram 20 mg were administered i.v. over 20 min and distentions were repeated. Afterwards, isobaric tone measurements were performed 30 min before and 90 min after ingestion of a meal. High-amplitude propagated contractions, colonic motility index, colonic compliance, sensitivity and colonic response to a meal after placebo or citalopram were compared by t-test and two-way ANOVA.

RESULTS

Citalopram induced a significant increase in colonic motility index (5.6 +/- 0.9 to 0.8 +/- 1.9 mL*min, P < 0.005) and high-amplitude propagated contractions (32 after citalopram vs. 2 after placebo, P < 0.05), which were associated with abdominal cramping. Administration of citalopram increased colonic compliance (10.3 +/- 1.5 vs. 14.5 +/- 2.2 mL/mmHg, P < 0.01) and inhibited colonic response to a meal (volume decrease 48 +/- 12 vs. 16 +/- 12 mL, P < 0.01).

CONCLUSIONS

Acute serotonin transporter inhibition in man increases colonic phasic contractility and the occurrence of high-amplitude propagated contractions, increases colonic compliance and suppresses the colonic tonic response to a meal. These data suggest that both release and elimination of 5-hydroxytryptamine by serotonin transporter are involved in the control of colonic motility in man.

Novel evidence for hypersensitivity of visceral sensory neural circuitry in irritable bowel syndrome patients

BACKGROUND & AIMS

Visceral hypersensitivity in irritable bowel syndrome (IBS) patients has been documented by evaluation of perceived stimulations that can reflect abnormalities of both sensory neurocircuitry and cognitive processes. The presence of actual neurohypersensitivity in human beings has not been documented separately. Because subliminal stimulations are free from the influence of stimulus-related cognitive processes, functional magnetic resonance imaging (fMRI) cortical response to these stimuli can be considered a measure of activity of the neural circuitry alone. The aim of this study was to compare quantitatively the cerebral cortical fMRI activity response to equal subliminal stimulations between IBS patients and age-matched controls.

METHODS

We studied 10 IBS patients and 10 healthy controls using a computerized barostat-controlled rectal distention device. fMRI activity volume and percent maximum signal intensity change for equal subliminal distention pressures were compared between controls and patients.

RESULTS

Three levels of subliminal distention pressures (eg, 10, 15, and 20 mm Hg), were represented in both controls and patients and were analyzed for fMRI response. In all 3 distention levels the fMRI activity volume in IBS patients was significantly larger than age- and sex-matched controls (P < .05). The percent maximum signal intensity change was similar between IBS patients and controls.

CONCLUSIONS

The volume of cerebral cortical activity response to equal subliminal distention pressures in IBS patients is significantly larger than in controls, documenting the existence of hypersensitivity of the neural circuitry in this patient group irrespective of stimulus-related cognitive processes.

Drugs affecting visceral sensitivity: ready for the prime time?

Visceral sensitivity has been recognized over the last decade as a frequent pathophysiological component of functional bowel disorders. Studies in animals and humans have identified numerous neurotransmitters involved in the processing of sensations from the gut to the brain. However, up to now none of them has actually been proven to have a marked clinical efficacy and the benefit comes rather from their action of bowel disturbances. Reproducible tests are lacking to detect visceral hypersensitivity in humans and distension tests are difficult to undertake in a clinical setting. Therefore, abnormal visceral sensitivity may not be regarded as a tool to select IBS patients as candidates for a given treatment.

Gabapentin reduces rectal mechanosensitivity and increases rectal compliance in patients with diarrhoea-predominant irritable bowel syndrome

BACKGROUND

Gabapentin has been shown to reduce elements of central sensitization in human experimental hyperalgesia. It remains uninvestigated whether gabapentin has beneficial effects for irritable bowel syndrome associated with visceral hypersensitivity.

AIMS

To evaluate the effects of gabapentin on sensory and motor function of the rectum in patients with diarrhoea-predominant irritable bowel syndrome.

METHODS

Forty patients with diarrhoea-predominant irritable bowel syndrome completed this randomized, double-blind, placebo-controlled, parallel-grouped study. All patients received a barostat study and were subsequently randomized for 5-day treatment with gabapentin 300 mg/day and then 600 mg/day or placebo. On day 6, after subjects had their morning dose, the barostat experiment was repeated.

RESULTS

The threshold pressures for bloating, discomfort and pain significantly increased after gabapentin, but not after placebo. Significant increase in the pressure and corresponding wall tension inducing discomfort or pain were observed in the gabapentin group, but not in the placebo group. Rectal compliance significantly increased after gabapentin, but not after placebo. The postprandial increase of rectal tone was not affected by gabapentin.

CONCLUSION

Our results show that gabapentin reduces rectal sensory thresholds through attenuating rectal sensitivity to distension and enhancing rectal compliance in diarrhoea-predominant irritable bowel syndrome patients. The clinical efficacy of this drug in irritable bowel syndrome patients warrants investigation.

Food-specific IgG4 antibody-guided exclusion diet improves symptoms and rectal compliance in irritable bowel syndrome

OBJECTIVE

Dietary modification improves symptoms in irritable bowel syndrome (IBS). Identification of offending foods by dietary elimination/re-challenge is cumbersome. IgG4 antibodies to common food antigens are elevated in IBS. The aim of this article was to evaluate the effect of exclusion diet based on IgG4 titres on IBS symptoms and rectal sensitivity and compliance.

MATERIALS AND METHODS

The study comprised 25 patients with IBS (3 M, 22 F, mean age 43 years, Rome II criteria). IgG4 titres to 16 foods (milk, eggs, cheese, wheat, rice, potatoes, chicken, beef, pork, lamb, soya bean, fish, shrimps, yeast, tomatoes and peanuts) were measured. Foods with titres >250 microg/l were excluded for 6 months. Symptom severity was assessed with a previously validated questionnaire at baseline, at 3 months and at 6 months. Rectal compliance and sensitivity were measured in 12 patients at baseline and at 6 months.

RESULTS

IgG4 antibodies to milk, eggs, wheat, beef, pork and lamb were commonly elevated. Significant improvement was reported in pain severity (p < 0.001), pain frequency (p = 0.034), bloating severity (p = 0.001), satisfaction with bowel habits (p = 0.004) and effect of IBS on life in general (p = 0.008) at 3 months. Symptom improvement was maintained at 6 months. Rectal compliance was significantly increased (p = 0.011) at 6 months but the thresholds for urge to defecate/discomfort were unchanged.

CONCLUSIONS

Food-specific IgG4 antibody-guided exclusion diet improves symptoms in IBS and is associated with an improvement in rectal compliance.

Facilitation of gastric compliance and cardiovascular reaction by repeated isobaric distension of the rat stomach

Gastric distension causes cardiovascular reactions and enhances gastric compliance. Here, we investigated how these responses are related to each other, whether they change upon repeated distension and which neural mechanisms are involved. Mean arterial blood pressure (MAP) in phenobarbital-anaesthetized rats was recorded from a carotid artery and gastric compliance determined with an electronic barostat. Runs of intermittent gastric distension were generated by stepwise increments (5 mmHg) of intragastric (IG) pressure. While gastric compliance peaked at IG pressures of 20 mmHg, the change in MAP (predominantly hypotension) was largest at IG pressures beyond 30 mmHg. Repeated distension enhanced the MAP response to IG pressures beyond 35 mmHg, whereas gastric compliance was facilitated primarily at IG pressures below 20 mmHg. This facilitation of gastric compliance depended on the magnitude of the preceding distension. The MAP response to distension was enhanced by nitric oxide synthase inhibition, inhibited by subdiaphragmatic vagotomy but hardly affected by coeliac ganglionectomy. The facilitation of gastric compliance was changed by vagotomy in a complex manner but left unaltered by the other interventions. These findings show that isobaric gastric distension elicits both MAP and gastric compliance responses whose characteristics, mechanisms and sensitization properties differ profoundly.

Characteristics of rectal perception are altered in irritable bowel syndrome

A hallmark symptom of irritable bowel syndrome (IBS) is a lower pain threshold during rectal distension, but the mechanism underlying this disorder remains unclear. Examining the relationship between physiological and perceptual responses to rectal distension can provide insight into the underlying peripheral or central dysfunction in IBS. Therefore, we carried out a study of the rectal sensations of urge to defecate, pain and unpleasantness in relation to the varying states of the rectum. Ten IBS patients and 13 healthy controls underwent six sets of isobaric rectal distensions. The first set was ascending stepwise distensions terminating upon report of moderate pain where verbal ratings of urge, pain, and unpleasantness were acquired. The remaining sets were phasic or tonic distensions at a single pressure eliciting either moderate urge or moderate pain intensity where subjects gave continuous ratings of urge or pain percepts. The McGill Pain Questionnaire (MPQ) was used to assess different qualities of the pain experience during single pressure distensions. Abnormalities in IBS patients included: (1) higher incidence of distensions where unpleasantness is greater than pain intensity, (2) significantly longer persistence of ratings after stimulus termination during phasic distensions eliciting either moderate urge or moderate pain, (3) significantly smaller ratings fluctuations during tonic distensions, and (4) significantly higher MPQ scores for painful tonic distensions. Our study demonstrates that IBS patients have abnormal temporal and intensity properties of rectal sensation. These can be accounted for by either altered peripheral neuromuscular processing and/or processing of ascending rectal input in the central nervous system.

Visceral sensitivity and symptoms in patients with constipation- or diarrhea-predominant irritable bowel syndrome (IBS): effect of a low-fat intraduodenal infusion

BACKGROUND

Visceral hypersensitivity is common in Irritable Bowel Syndrome (IBS) patients, and symptoms exacerbate postprandially. Yet the effects of nutrients on visceral sensitivity and symptoms in these patients have not been fully explored.

AIMS

To evaluate the differences of visceral sensitivity and symptoms in healthy subjects and IBS patients during fasting and intraduodenal lipids infusion.

METHODS

Graded rectal distensions at fixed tension levels were performed in 16 IBS patients (8 IBS-C and 8 IBS-D) and 6 healthy subjects before and during intraduodenal lipids infusion at 0.5 kcal/min. Tension levels were increased in 4 gr increments up to 64 gr or discomfort during both conditions. At each step, perception and symptoms were measured by means of a validated questionnaire.

RESULTS

In basal conditions, perception thresholds in IBS patients and health were, respectively, 8 +/- 2 gr versus 32 +/- 9 gr (p < 0.001) with no changes during lipids. Intraduodenal lipids infusion significantly lowered threshold of discomfort in IBS patients in comparison to fasting (24 +/- 6 gr vs 34 +/- 4 gr; p < 0.05), while health tolerated all distension without discomfort. No differences of compliance, perception, or discomfort were observed between the two subgroups of patients at each tension step. The predominant symptom elicited in patients with IBS-C was abdominal pain (54%), while patients with IBS-D exhibited urgency (63%, p < 0.005); this pattern was maintained during lipids.

CONCLUSIONS

Intraduodenal lipids increase visceral sensitivity in both IBS-C and IBS-D; symptoms specificity in response to rectal distension is maintained in the postprandial period. Lipids may be responsible for the postprandial symptoms exacerbation in IBS.

Sex-based differences in gastrointestinal pain

Recent interest has focused on sex-related differences in irritable bowel syndrome (IBS) physiology and treatment responsiveness to novel pharmacologic therapies. Similar to a variety of other chronic pain conditions and certain affective disorders, IBS is more prevalent amongst women, both in population-based studies as well as in clinic-based surveys. Non-painful gastrointestinal symptoms, constipation and somatic discomfort are more commonly reported by female IBS patients. While perceptual differences to rectosigmoid stimulation are only observed following repeated noxious stimulation of the gut, sex-related differences in certain sympathetic nervous system (SNS) responses to rectosigmoid stimulation are consistently seen. Consistent with experimental findings in animals, current evidence is consistent with a pathophysiological model which emphasizes sex-related differences in autonomic and antinociceptive responses to certain visceral stimuli.

Role of serotonin in the pathophysiology of the irritable bowel syndrome

The irritable bowel syndrome (IBS) is a complex disorder that is associated with altered gastrointestinal motility, secretion, and sensation. Serotonin (5-HT) is an important neurotransmitter and paracrine signalling molecule in the gastrointestinal tract. 5-HT release from enterochromaffin (EC) cells initiates peristaltic, secretory, vasodilatory, vagal and nociceptive reflexes. The enteric nervous system (ENS) comprises a semiautonomous effector system that is connected to the central autonomic network. Parasympathetic and sympathetic nerves modulate the ENS via afferent and efferent communications. Ongoing, bidirectional brain-gut interactions involving 5-HT pathways occur that significantly influence the effector systems. Altered 5-HT signalling may lead to both intestinal and extraintestinal symptoms in IBS. 5-HT directly and indirectly affects intestinal motor and secretory function and abnormalities may lead to either constipation or diarrhea. 5-HT modulates sensation and perception of visceral stimulation at peripheral and central sites. Therapeutic agents targeting altered 5-HT signalling may provide new, effective treatments for patients with IBS.

Effect of sex steroids on colonic distension-induced delay of gastric emptying in rats

BACKGROUND AND AIM

The objective of the present study was to examine the effect of gonadal hormones on gastric motor response to non-noxious and noxious stimuli of colonic distension.

METHODS

Male Wistar albino rats were used. Under ketamine anesthesia some rats underwent castration (n = 24), while the rest of the rats were sham-operated (n = 67) and divided into different groups (n = 7-8 per group). On the 15th day of surgery, liquid gastric emptying studies were commenced.

RESULTS

Non-noxious (P < 0.05) or noxious (P < 0.01) colonic distension inhibited gastric emptying rate. Estradiol pretreatment (20 micro g/kg per day, for 5 days, s.c.) inhibited gastric motility, while estradiol pretreatment or castration of the rats prior to noxious distension prevented the delay in gastric emptying. In contrast, blockade of testosterone receptors had no effect on the delay in gastric emptying induced by either modes of distension.

CONCLUSIONS

The results suggest that sex steroids have a modulatory role on the feedback control of gastric motility induced by noxious colonic distension.

Alterations of sensori-motor functions of the digestive tract in the pathophysiology of irritable bowel syndrome

Pathophysiology of irritable bowel syndrome (IBS) is based upon multiple factors that have been organised in a comprehensive model centred around the brain-gut axis. The brain-gut axis encompasses nerve pathways linking the enteric and the central nervous systems and contains a large proportion of afferent fibres. Functionally and anatomically, visceral nerves are divided in to two categories: the parasympathetic pathways distributing to the upper gut through the vagi and to the hindgut, through the pelvic and pudendal nerves, and the sympathetic pathways, arising form the spinal cord and distributing to the midgut via the paravertebral ganglia. Several abnormalities of gut sensori-motor function have been described in patients with IBS. Abnormal motility patterns have been described at the intestinal and colonic levels. Changes in colonic motility are mainly related to bowel disturbances linked to IBS but do not correlate with pain. More recently, visceral hypersensitivity has been recognised as a main characteristic of patients with IBS. It is defined by an exaggerated perception of luminal distension of various segments of the gut and related to peripheral changes in the processing of visceral sensations as well as modulation of perception by centrally acting factors including mood and stress. Viscero-visceral reflexes link the two edges of the brain-gut axis and may account for the origin of symptoms in some pathological conditions. Recent advances in the understanding of the role of myenteric plexus allowed recognition of several neurotransmitters involved at the level of both the afferent and efferent pathways. Targeting the receptors of these neurotransmitters is a promising way for development of new treatments for IBS.