Compliance, tone and sensitivity of the rectum in different subtypes of irritable bowel syndrome

Postprandial effect of gastrointestinal hormones and gastric activity in patients with irritable bowel syndrome

Altered gut regulation, including motor and secretory mechanisms, is characteristic of irritable bowel syndrome (IBS). The severity of postprandial symptoms in IBS patients is associated with discomfort and pain; gas-related symptoms such as bloating and abdominal distension; and abnormal colonic motility. The aim of this study was to assess the postprandial response, i.e., gut peptide secretion and gastric myoelectric activity, in patients with constipation-predominant IBS. The study was conducted on 42 IBS patients (14 males, 28 females, mean age 45.1 ± 15.3 years) and 42 healthy participants (16 males, 26 females, mean age 41.1 ± 8.7 years). The study assessed plasma gut peptide levels (gastrin, CCK-Cholecystokinin, VIP-Vasoactive Intestinal Peptide, ghrelin, insulin) and gastric myoelectric activity obtained from electrogastrography (EGG) in the preprandial and postprandial period (meal-oral nutritional supplement 300 kcal/300 ml). Mean preprandial gastrin and insulin levels were significantly elevated in IBS patients compared to the control group (gastrin: 72.27 ± 26.89 vs. 12.27 ± 4.91 pg/ml; p < 0.00001 and insulin: 15.31 ± 12.92 vs. 8.04 ± 3.21 IU/ml; p = 0.0001), while VIP and ghrelin levels were decreased in IBS patients (VIP: 6.69 ± 4.68 vs. 27.26 ± 21.51 ng/ml; p = 0.0001 and ghrelin: 176.01 ± 88.47 vs. 250.24 ± 84.55 pg/ml; p < 0.0001). A nonsignificant change in the CCK level was observed. IBS patients showed significant changes in postprandial hormone levels compared to the preprandial state-specifically, there were increases in gastrin (p = 0.000), CCK (p < 0.0001), VIP (p < 0.0001), ghrelin (p = 0.000) and insulin (p < 0.0001). Patients with IBS showed reduced preprandial and postprandial normogastria (59.8 ± 22.0 vs. 66.3 ± 20.2%) compared to control values (83.19 ± 16.7%; p < 0.0001 vs. 86.1 ± 9.4%; p < 0.0001). In response to the meal, we did not observe an increase in the percentage of normogastria or the average percentage slow-wave coupling (APSWC) in IBS patients. The postprandial to preprandial power ratio (PR) indicates alterations in gastric contractions; in controls, PR = 2.7, whereas in IBS patients, PR = 1.7, which was significantly lower (p = 0.00009). This ratio reflects a decrease in gastric contractility. Disturbances in the postprandial concentration of gut peptides (gastrin, insulin and ghrelin) in plasma may contribute to abnormal gastric function and consequently intestinal motility, which are manifested in the intensification of clinical symptoms, such as visceral hypersensitivity or irregular bowel movements in IBS patients.

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.

Associations among neurophysiology measures in irritable bowel syndrome (IBS) and their relevance for IBS symptoms

Abnormal gut-brain interactions are common in irritable bowel syndrome (IBS), but the associations between neurophysiological measures and their relation to gastrointestinal (GI) symptoms are poorly understood. Our aim was to explore these relationships and define the most relevant neurophysiology measures for GI symptom severity in IBS. IBS patients underwent small intestinal motility (manometry; fasted and fed contraction frequency, phase III time) and secretion (transmural potential difference), rectal sensorimotor (barostat; sensory thresholds, tone response, compliance), autonomic nervous system (baroreceptor sensitivity and effectiveness), and colonic motor function (transit time) examinations. GI symptom severity (GSRS-IBS), and anxiety and depression (HAD) as a proxy measure of central nervous system (CNS) dysfunction, were assessed. In total 281 IBS patients (Rome II criteria) were included (74% females, median age 36 [interquartile range 28-50] years). Significant correlations between neurophysiology measures were stronger within, rather than between, different neurophysiological examinations. The strongest neurophysiology-symptom correlations occurred between a combination of CNS and visceral sensitivity parameters, and GSRS-IBS total score and pain domain (ρ = 0.40, p < 0.001, and ρ = 0.38, p < 0.001). Associations between GI symptoms in IBS and individual and combinations of neurophysiological factors occurred, primarily in CNS and visceral sensitivity measures, providing new insights into the clinical presentation of IBS.

Mechanical analysis of intestinal contractility in a neonatal maternal deprivation irritable bowel syndrome rat model

The aims of the present study are to investigate biomechanical properties and provide mechanical analysis of contractility in ileum and colon in a neonatal maternal deprivation (NMD) irritable bowel syndrome (IBS) rat model. Mechanical testing was done on segments from ileum and colon in 25 IBS rats and 13 Control rats. Morphometric data were obtained from digitized images of the segments at no-load and zero-stress states. Pressure and diameter changes were measured during flow and ramp distensions under active and passive experimental conditions. Circumferential stresses (force per area) and strains (deformation) were computed with referenced to the zero-stress state. The contraction frequency was analyzed. Contraction thresholds and maximum contraction amplitude were calculated in terms of mechanical stress and strain. Compared with controls, the IBS rats had lower body weight (P < 0.01), smaller colonic opening angle (P < 0.05), higher colonic contraction frequency (P < 0.05 and P < 0.01) and lower contraction thresholds of pressure, stress and strain in both ileum and colon (P < 0.05 and P < 0.01). The maximum contraction pressure, stress and strain did not differ between IBS and Control groups (P > 0.05). In conclusion, the pressure, stress, and strain to evoke contractility in ileum and colon were lower whereas the frequency of induced colon contractions was higher in NMD IBS rats compared to normal rats. Furthermore, zero-stress state remodeling occur in colon in NMD IBS rats. Further studies on the association between intestinal biomechanical properties, hypersensitivity and afferent signaling in the IBS animal models are warranted.

Plausibility criteria for putative pathophysiological mechanisms in functional gastrointestinal disorders: a consensus of experts

BACKGROUND AND AIMS

The functional gastrointestinal disorders (FGIDs) are extremely common conditions associated with a considerable personal, social and health economic burden. Managing FGIDs in clinical practice is challenging because of the uncertainty of symptom-based diagnosis, the high frequency of overlap between these conditions and the limited efficacy of available therapies. It has often been argued that successful drug development and management of FGIDs requires knowledge of the underlying pathophysiology. Numerous and highly variable candidate pathophysiological mechanisms have been implicated in the generation of FGID symptoms, but there is no current consensus on how to best define the relevance of these disturbances.

METHODS

A group of international experts on FGIDs developed plausibility criteria that should be fulfilled by relevant pathophysiological mechanisms in FGIDs.

RESULTS

Five criteria are proposed: (1) the presence of the abnormality in a subset of patients, (2) temporal association between proposed mechanism and symptom(s), (3) correlation between the level of impairment of the mechanism and symptom(s), (4) induction of the symptom(s) by provoking the pathophysiological abnormality in healthy subjects and (5) treatment response by a therapy specifically correcting the underlying disorder or congruent natural history of symptoms and dysfunction in the absence of specific therapy. Based on strength of evidence for these five criteria according to the Grading of Recommendations Assessment, Development and Evaluation system, a plausibility score can be calculated for each mechanism.

CONCLUSION

Evaluation of the strength of evidence for candidate pathophysiological abnormalities fulfilling these five plausibility criteria will help to identify the most relevant mechanisms to target for novel diagnostic approaches and for the development of new therapies.

Dietary and pharmacological treatment of abdominal pain in IBS

This review introduces the principles of visceral sensation and appraises the current approaches to management of visceral pain in functional GI diseases, principally IBS. These approaches include dietary measures including fibre supplementation, low fermentable oligosaccharides, disaccharides, monosaccharides and polyols diet, and pharmacological approaches such as antispasmodics, peppermint oil, antidepressants (tricyclic agents, selective serotonin reuptake inhibitors), 5-HT₃ receptor antagonists (alosetron, ondansetron, ramosetron), non-absorbed antibiotic (rifaximin), secretagogues (lubiprostone, linaclotide), μ-opioid receptor (OR) and κ-OR agonist, δ-OR antagonist (eluxadoline), histamine H1 receptor antagonist (ebastine), neurokinin-2 receptor antagonist (ibodutant) and GABAergic agents (gabapentin and pregabalin). Efficacy and safety are discussed based on pivotal trials or published systematic reviews and meta-analysis, expressing ORs or relative risks and their 95% CIs. Potential new approaches may be based on recent insights on mucosal expression of genes, and microRNA and epigenetic markers in human biopsies and in animal models of visceral hypersensitivity.The objectives of this review are to appraise the physiology and anatomy of gut sensation and the efficacy in the relief of visceral pain (typically in IBS) of several classes of therapies. These include fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) and different classes of medications (box 1). Box 1Classes of pharmacological agents for visceral painAntidepressants (tricyclic agents, selective serotonin reuptake inhibitors)Peppermint oil5-HT₃ receptor antagonists (alosetron, ondansetron, ramosetron)Non-absorbed antibiotic (rifaximin)Secretagogues (lubiprostone, linaclotide)μ-Opioid receptor (OR) and κ-OR agonist and δ-OR antagonist (eluxadoline)Histamine H1 receptor antagonist (ebastine)Neurokinin-2 receptor antagonist (ibodutant)GABAergic agents (gabapentin and pregabalin).

Intestinal secretory mechanisms in irritable bowel syndrome-diarrhea

Although diarrhea is the predominant bowel dysfunction in as many as one-third of patients with irritable bowel syndrome (IBS), it is unclear whether there is a specific disorder of intestinal fluid or electrolyte secretion in IBS. Diarrhea is generally considered a result of accelerated colonic transit in patients with IBS. Although a primary secretory diathesis has not been well-documented in patients with IBS with diarrhea (IBS-D), several mechanisms that could potentially contribute to intestinal secretion have been reported. Some of these mechanisms also influence motor and secretory dysfunctions that contribute to the pathophysiology of IBS-D. We review the evidence supporting secretion in IBS-D caused by peptides and amines produced by enteroendocrine cells or submucosal neurons, enterocyte secretory processes, and intraluminal factors (bile acids and short-chain fatty acids). Understanding these mechanisms and developing clinical methods for their identification could improve management of patients with IBS-D.

The quest for biomarkers in IBS-where should it lead us?

Irritable bowel syndrome (IBS) is a prevalent functional gastrointestinal disorder which represents a major cost to health-care services. The diagnosis of IBS is currently performed by means of symptom-based diagnostic criteria, but there has been an ongoing interest in developing biomarkers which could simplify the diagnosis and/or evaluating the effect of treatments. This article reviews the current literature concerning the proposed biomarkers including those of altered gut motility, of visceral hypersensitivity, of abnormal brain mechanisms, of serum, fecal and mucosal inflammation and of increased intestinal permeability.

Interaction between preprandial and postprandial rectal sensory and motor abnormalities in IBS

BACKGROUND AND AIMS

Rectal sensory and motor interactions in patients with IBS have not been studied in detail. The aim of this study was to evaluate fasting and postprandial rectal sensorimotor characteristics and their interactions in IBS compared with healthy controls.

DESIGN

We included 274 patients with IBS and 34 controls. All subjects underwent a rectal barostat study before and 60 min after a standardised liquid meal (800 kcal; 60% fat). Sensory thresholds, intensity of sensations, viscerosomatic referral and compliance were measured. During 15 min before the first distension sequence and until 50 min after meal intake, rectal balloon volumes were registered in 5 min intervals at operating pressure to quantify rectal tone. Mixed models were used to analyse the rectal tone response over time.

RESULTS

Rectal sensory thresholds and compliance were decreased and viscerosomatic referral areas increased in patients with IBS compared with controls. Meal intake increased rectal sensitivity, compliance and referral areas in patients and controls and the same proportions of patients were hypersensitive to distension before and after meal intake. There was a higher basal rectal tone in IBS and a significantly different rectal tone response after meal intake in patients with IBS compared with controls and, interestingly, also in IBS with rectal hypersensitivity (defined in the preprandial state), compared with normosensitive patients.

CONCLUSIONS

Meal intake affects rectal sensorimotor function in IBS and health. Importantly, the rectal tone responses to a high-caloric meal are different between patients with IBS and controls, as well as between hypersensitive and normosensitive patients with IBS.

Autonomic rectal dysfunction in patients with multiple sclerosis and bowel symptoms is secondary to spinal cord disease

BACKGROUND

Most patients with multiple sclerosis report bowel symptoms, but the underlying pathophysiology is unclear.

OBJECTIVE

We hypothesize that rectal dysfunction in multiple sclerosis is secondary to involvement of the spinal cord by the disease and that this can be measured by assessing rectal compliance.

DESIGN

This was a case-control study.

SETTINGS

The study took place in a neurogastroenterology clinic and tertiary referral center.

PATIENTS

Forty-five patients with multiple sclerosis, 19 with a spinal cord injury above T5, and 25 normal control subjects were included in this study. Patients with multiple sclerosis were subdivided into 2 groups according to the Expanded Disability Status Scale, below 5 (multiple sclerosis minor disability, n = 25) or above 5 (multiple sclerosis major disability, n = 20), as a reflection of spinal cord involvement.

MAIN OUTCOME MEASURES

Rectal compliance, Wexner constipation, and Wexner incontinence scores were measured.

RESULTS

Data are presented as mean and SD. Expanded Disability Status Scale correlated with rectal compliance but not with Wexner constipation or Wexner incontinence scores. Post hoc analysis showed no significant difference in Wexner constipation and Wexner incontinence between the 2 multiple sclerosis groups.

LIMITATIONS

Limitations to this study include the lack of an asymptomatic group with multiple sclerosis and the small sample size to evaluate bowel symptoms.

CONCLUSIONS

Rectal compliance correlates with disability, and observed alterations in the rectal properties are secondary to spinal cord involvement. Our findings suggest that, in patients with neurologic impairment, rectal compliance is a surrogate of reflex activity of the spinal cord regulating rectal function and both a potential predictor of outcome and target for treatment. Multiple sclerosis patient subgroups had similar symptom burden, arguing that bowel dysfunction is multifactorial.

Serotonin receptors and their role in the pathophysiology and therapy of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract characterized by abdominal discomfort, pain and changes in bowel habits, often associated with psychological/psychiatric disorders. It has been suggested that the development of IBS may be related to the body's response to stress, which is one of the main factors that can modulate motility and visceral perception through the interaction between brain and gut (brain-gut axis). The present review will examine and discuss the role of serotonin (5-hydroxytryptamine, 5-HT) receptor subtypes in the pathophysiology and therapy of IBS.

METHODS

Search of the literature published in English using the PubMed database.

RESULTS

Several lines of evidence indicate that 5-HT and its receptor subtypes are likely to have a central role in the pathophysiology of IBS. 5-HT released from enterochromaffin cells regulates sensory, motor and secretory functions of the digestive system through the interaction with different receptor subtypes. It has been suggested that pain signals originate in intrinsic primary afferent neurons and are transmitted by extrinsic primary afferent neurons. Moreover, IBS is associated with abnormal activation of central stress circuits, which results in altered perception during visceral stimulation.

CONCLUSIONS

Altered 5-HT signaling in the central nervous system and in the gut contributes to hypersensitivity in IBS. The therapeutic effects of 5-HT agonists/antagonists in IBS are likely to be due also to the ability to modulate visceral nociception in the central stress circuits. Further studies are needed in order to develop an optimal treatment.

Neorectal hyposensitivity after neoadjuvant therapy for rectal cancer

BACKGROUND AND PURPOSE

Preoperative radiotherapy for rectal cancer has a detrimental effect on long-term anorectal function and quality of life, additional to that observed after rectal resection. The exact physiological mechanisms for the excess impairment remain unknown. We aimed to investigate neorectal and anal sphincter properties in patients treated with neoadjuvant therapy (NT) prior to total mesorectal excision (TME).

MATERIAL AND METHODS

Sixteen patients (NT+ patients) were examined by multimodal neorectal stimulation and standard anorectal physiological testing. Data were compared to the results of 23 patients, who underwent TME without NT (NT- patients).

RESULTS

NT+ patients had elevated sensory thresholds to heat (median temperature, 60 vs. 55 °C; p<0.01) and mechanical distension (median tension, 2513 vs. 1521 mmHg mm; p=0.05) in the fasting state, and altered perception of the sensory response to heat (p=0.01) and cold (p=0.01) compared to NT- patients. No differences in the biomechanical properties of the neorectal wall were detected. Anal resting pressure was lower in NT+ patients compared to NT- patients (median pressure, 31 vs. 45 cm H2O; p=0.05).

CONCLUSIONS

Pelvic radiotherapy causes neorectal hyposensitivity to mechanical and thermal stimuli in patients receiving NT prior to TME surgery for rectal cancer, possibly due to impaired afferent nerve function.

Irritable bowel syndrome with constipation: a European-focused systematic literature review of disease burden

OBJECTIVE

To conduct a systematic literature review to assess burden of disease and unmet medical needs in patients with irritable bowel syndrome (IBS) with constipation (IBS-C), with a focus on five European countries (France, Germany, Italy, Spain, UK).

METHODS

MEDLINE, EMBASE, and grey literature searches were carried out using terms for IBS and constipation, to identify studies reporting epidemiological, clinical, humanistic, or economic outcomes for IBS-C, published between 2000 and 2010.

RESULTS

Searches identified 885 unique abstracts and 33 supplementary articles, of which 100 publications and six grey literature sources met the inclusion criteria. Among patients with IBS, the prevalence estimates of IBS-C ranged from 1 to 44%. Co-morbid conditions, such as personality traits, psychological distress, and stress, were common. Patients with IBS-C had lower health-related quality-of-life (HRQoL) compared with the general population, and clinical trials suggested that effectively treating IBS-C improves HRQoL. The European societal cost of IBS-C is largely unknown, as no IBS-C-specific European cost-of-illness studies were identified. Two cost analyses demonstrated the substantial societal impact of IBS-C, including reduced productivity at work and work absenteeism. Guidelines offered similar recommendations for the diagnosis and management of IBS; however, recommendations specifically for IBS-C varied by country. Current IBS-C treatment options have limited efficacy and the risk:benefit profile of early 5-HT(4) agonists restricts clinical use.

CONCLUSIONS

This systematic review indicates a clear need for European-focused IBS-C burden-of-disease and cost-of-illness studies to address identified evidence gaps. There is a need for new therapies for IBS-C that are effective, well tolerated, and have a positive impact on HRQoL.

Altered neuro-endocrine-immune pathways in the irritable bowel syndrome: the top-down and the bottom-up model

The interaction between the brain and the gut as a pathological mechanism of functional gastrointestinal disorders has been recently recognized in the pathophysiology of the irritable bowel syndrome. Communication between central nervous system and enteric nervous system is two-directional: the brain can influence the function of the enteric nervous system and the gut can influence the brain via vagal and sympathetic afferents. In patients with irritable bowel syndrome, symptoms may be caused by alterations either primarily in the central nervous system (top-down model), or in the gut (bottom-up model), or in a combination of both. The brain-gut axis may be stimulated by various stressors either directed to the central nervous system (exteroreceptive stress) or to the gut (interoceptive stress). Particularly, clinical evidence suggest that in complex and multifactorial diseases such as irritable bowel syndrome, psychological disorders represent significant factors in the pathogenesis and course of the syndrome. Neuroimaging techniques have shown functional differences between central process in healthy subjects and patients with irritable bowel syndrome. Moreover, a high prevalence of psychological/psychiatric disorders have been reported in IBS patients compared to controls. Several data also suggest an alteration of neuro-endocrine and autonomic output to the periphery in these patients. This review will examine and discuss the complex interplay of neuro-endocrine-immune pathways, closely associated with neuropsychiatric disorders.

Rectal hyposensitivity

Impaired or blunted rectal sensation, termed rectal hyposensitivity (RH), which is defined clinically as elevated sensory thresholds to rectal balloon distension, is associated with disorders of hindgut function, characterised primarily by symptoms of constipation and fecal incontinence. However, its role in symptom generation and the pathogenetic mechanisms underlying the sensory dysfunction remain incompletely understood, although there is evidence that RH may be due to 'primary' disruption of the afferent pathway, 'secondary' to abnormal rectal biomechanics, or to both. Nevertheless, correction of RH by various interventions (behavioural, neuromodulation, surgical) is associated with, and may be responsible for, symptomatic improvement. This review provides a contemporary overview of RH, focusing on diagnosis, clinical associations, pathophysiology, and treatment paradigms.

Rectal hypersensitivity as hallmark for irritable bowel syndrome: defining the optimal cutoff

BACKGROUND

Visceral hypersensitivity is a frequently observed hallmark of irritable bowel syndrome (IBS). Studies have reported differently about the presence of visceral hypersensitivity in IBS resulting from lack of standardization of the barostat procedure and due to different criteria used to assess hypersensitivity. We aimed to calculate the optimal cutoff to detect visceral hypersensitivity in IBS.

METHODS

A total of 126 IBS patients and 30 healthy controls (HC) were included for assessment of visceroperception by barostat. Pain perception was assessed on a visual analogue scale (VAS). ROC-curves were used to calculate optimal discriminative cutoff (pressure and VAS-score) between IBS patients and HC to define hypersensitivity. Furthermore, pain perception to distension sequences below the pressure threshold for hypersensitivity was defined as allodynia.

KEY RESULTS

Irritable bowel syndrome patients showed increased visceroperception compared to HC. Thresholds for first sensation and first pain were lower in IBS patients VS HC (P < 0.01). ROC-curves showed optimal discrimination between IBS patients and HC at 26 mmHg with a VAS cutoff ≥20 mm. Using this criterion, hypersensitivity percentages were 63.5% and 6.6% in IBS patients and HC, respectively. No significant differences were observed between IBS subtypes. Allodynia was found in a small number of patients (11%).

CONCLUSIONS & INFERENCES

Optimal cutoff for visceral hypersensitivity was found at pressure 26 mmHg with a VAS ≥20 mm, resulting in 63.5% of IBS patients being hypersensitive and 11% being allodynic. Standardization of barostat procedures and defining optimal cutoff values for hypersensitivity is warranted when employing rectal barostat measurements for research or clinical purposes.

Sigmoid compliance and visceral perception in spinal cord injury patients

Intestinal motor and sensory dysfunctions in traumatic complete or incomplete spinal cord injury (SCI) are frequent and result in altered mechanisms of defecation. The aim of this study is to investigate sigmoid compliance and perception in chronic SCI patients. Sigmoid responses to fixed-tension distentions were assessed using a tensostat in six patients (six men, 42 ± 4 years) with chronic complete transection of the spinal cord (high-SCI; five tetraplegic C5-C7 and one paraplegic T4-T6) and impaired evacuation (i.e. constipation). A group of 10 healthy individuals (six men, 25 ± 1 years) served as controls. SCI patients had higher sigmoid compliance at the highest distention level than the controls (10.3 ± 2.4 vs. 5.1 ± 0.8 ml/mmHg; P<0.05). Perception scores at first sensation were higher in SCI patients (2.3 ± 0.7 vs. 1.1 ± 0.1; P<0.05), but were not different at the highest distention levels (3.7 ± 0.8 vs. 3 ± 1; NS). The most commonly reported sensation by patients was distention/bloating and was referred less commonly to the hypogastrium compared with distention/bloating in controls. An increased sigmoid compliance can be detected in constipated SCI patients. The preservation of some degree of visceral sensations, although abnormally referred, could imply the occurrence of sensory input remodeling at the spinal level.

The effects of sildenafil on rectal sensitivity and tone in patients with the irritable bowel syndrome

BACKGROUND

Visceral tone supposedly affects gut sensitivity in irritable bowel syndrome (IBS). Sildenafil increases nitric oxide and influences visceral compliance.

AIM

To evaluate the effects of sildenafil tone inhibition on rectal sensitivity.

METHODS

Eight controls and 21 IBS patients (Rome II) were enrolled in a double-blind study, after dosing with placebo or sildenafil (50 mg p.o.). Thresholds for first sensation, first desire to defecate, pain and supraliminar pain were the sensory endpoints, measured with a barostat and 600-mL rectal bag. Pain (100-mm VAS) and depression-anxiety (Hamilton questionnaire) were scored.

RESULTS

Irritable bowel syndrome rectal compliance and sensory-endpoint thresholds were similar to controls. Five IBS patients had pain threshold lower than controls 95% confidence interval (hypersensitive). Depression score was greater in IBS than controls (11.9 ± 1.3 vs. 6.3 ± 2.5, P = 0.036). In IBS, pain intensity was nonsignificantly higher (37.6 ± 5.3 mm vs. 23.4 ± 8.5 mm, P = 0.064) and supraliminar pain intensity was greater (45.6 ± 5.4 mm vs. 25.9 ± 5.1 mm, P = 0.044) than controls. IBS rectal relaxation increased volume (155.4 ± 41.3 mL vs. 118.8 ± 47.7 mL, P = 0.004) and tension (193.1 ± 118.6 mmHg mL(-1) vs. 133.2 ± 98.1 mmHg mL(-1) , P = 0.019) for triggering first desire to defecate but not for other perceptions. Sildenafil increased volume for both first desire to defecate and pain in the hypersensitive IBS patients. Sildenafil increased rectal compliance only in diarrhoea-IBS. Mixed-IBS obtained higher anxiety (12.9 ± 1.3 vs. 5.9 ± 3.1, P < 0.05) and depression scores (13.9 ± 1.9 vs. 6.3 ± 2.5, P < 0.05) and reported more intense supraliminar pain (53.6 ± 9.8 mm vs. 25.9 ± 5.1 mm, P < 0.05) than controls.

CONCLUSIONS

Rectal relaxation following dosing with sildenafil 50 mg increased the first desire to defecate threshold in IBS as a whole, but decreased pain only in the hypersensitive subset. Mixed-IBS presented higher supraliminar pain and anxiety-depression scores.

Alternative procedure to shorten rectal barostat procedure for the assessment of rectal compliance and visceral perception: a feasibility study

BACKGROUND

Barostat methodology is widely used for assessing visceral perception. Different barostat protocols are described with respect to the measurement of rectal compliance and visceral perception. The choice of protocols affects the duration, which is normally 60-90 min, and accuracy of the procedure. This study aimed to shorten the procedure by using the semi-random distension protocol for both compliance and visceral perception measurement and a correction based on rectal capacity (RC) instead of minimal distension pressure (MDP).

METHODS

Twelve irritable bowel syndrome (IBS) patients (7 females) and 11 healthy controls (8 females) underwent a barostat procedure. Compliance was determined during both a staircase distension and a semi-random protocol. Visceral perception data were compared as a function of pressure or relative volume, corrected for MDP or RC, respectively.

RESULTS

Compliance measurement using the semi-random protocol instead of the staircase distension protocol resulted in an overestimation in healthy volunteers, but not in IBS patients. The overall conclusion that IBS patients had a lower compliance compared to controls was not different between protocols. Data presentation of the visceral perception scores as a function of corrected volume instead of pressures corrected for MDP did not alter the conclusion that sensation scores in IBS patients were higher as compared to healthy controls.

CONCLUSIONS

This study showed that barostat procedures may be shortened by approximately 20 min, without losing the ability to discriminate between healthy controls and IBS patients. A correction for RC instead of MDP may improve the accuracy of the procedure.

Randomised clinical trial: the clinical effects of a novel neurokinin receptor antagonist, DNK333, in women with diarrhoea-predominant irritable bowel syndrome

BACKGROUND

Neurokinin receptors may play an important role in the visceral hypersensitivity and exaggerated motor/secretory activity associated with diarrhoea-predominant irritable bowel syndrome (IBS-D).

AIM

To evaluate the effects of DNK333, a novel neurokinin antagonist, in women with IBS-D.

METHODS

In two consecutive phase II studies, women with IBS-D were randomised to twice-daily (b.d.) DNK333 25 mg, DNK333 100 mg or placebo for 2 weeks (Trial 1), or DNK333 25 mg b.d. or placebo for 4 weeks (Trial 2). Primary efficacy variables studied were change from baseline of stool form at week 2, and satisfactory relief of IBS-related abdominal pain/discomfort and global IBS-D symptoms. Secondary efficacy variables, pharmacokinetics and safety were also evaluated.

RESULTS

In total, 315 subjects were randomised. There were no statistically significant differences between treatment groups for the primary efficacy variables. However, analysis of combined data from both trials revealed significant differences favouring DNK333 25 mg over placebo for satisfactory relief of IBS-related abdominal pain/discomfort and global IBS-D symptoms. Trends favouring improvement with DNK333 25 mg vs. placebo were seen for all secondary efficacy variables. DNK333 had a safety profile similar to placebo.

CONCLUSIONS

DNK333 25 mg b.d. appears to be effective and well tolerated in women with IBS-D. Further studies with neurokinin antagonists are warranted.

Anorectal function and dyssynergic defecation in different subgroups of patients with irritable bowel syndrome

PURPOSE

The purpose of this study was to evaluate anorectal function in different subgroups of patients with irritable bowel syndrome (IBS), including those with mixed bowel habits.

MATERIALS AND METHODS

Sixty-six IBS patients selected according to Rome III criteria (39 female and 27 male patients; mean age, 41.5 +/- 15.4) and 20 subjects in the control group (13 female and 7 male patients; mean age, 41.4 +/- 13.7) were examined. The IBS patients were divided into three subgroups according to bowel movement pattern: patients with constipation (27%), patients with diarrhea (27%), and patients with mixed bowel habits (46%). Anorectal manometry and rectal distension test were performed using a four-lumen water-perfused catheter with a polyethylene balloon.

RESULTS

No significant differences in manometric parameters between the subgroups of IBS patients and the control group were found, except for pelvic floor dyssynergia (PFD), which was more frequent in all subgroups of IBS (41% of patients) than in controls (5% of subjects) (p < 0.01). Lower rectal pain threshold was observed particularly in IBS patients with diarrhea and mixed bowel habits (p < 0.01).

CONCLUSION

Manometric parameters characterizing anal sphincter function are not correlated with the predominant bowel movement pattern in IBS. The features of PFD are significantly more frequent in all subgroups of IBS patients than in controls, suggesting that, in general, IBS patients show changes in the mobility of the pelvic floor. Hypersensitivity to rectal distension is commonly observed in IBS, but it does not seem to be a highly specific marker of the disorder.

Colorectal and rectocolonic reflexes in canines: involvement of tone, compliance, and anal sphincter relaxation

Distention of the proximal colon may have inhibitory or excitatory effects on the rectum and vice versa. The reflexes between the proximal colon and the rectum have not been well studied due to difficulties in accessing the proximal colon. The aim of this study was to investigate the reflex responses and their mechanisms between the proximal colon and the rectum in consideration of distention-related changes in tone and compliance of these regions as well as anal sphincter relaxation in a canine model. Proximal colon/rectal tone, compliance, and anal sphincter relaxation were investigated in six dogs chronically implanted with a proximal colon cannula while in the fasting state and during proximal colon distention or rectal distention. It was found that: 1) both rectal distention and proximal colon distention significantly and substantially decreased the compliance of the opposite regions, and guanethidine abolished proximal colon distention-induced changes in rectal compliance; 2) rectal/proximal colon distension decreased proximal colonic/rectal tone, and guanethidine abolished both of these inhibitory effects; 3) the anal sphincter was more sensitive to rectal distention than proximal colon distention; and 4) the minimal distention pressure required to induce anal inhibitory reflex was lower for rectal distention than proximal colon distention. It was concluded that distention-related changes in tone and compliance suggest the long inhibitory reflexes between the proximal colon and the rectum with the sympathetic involvement in rectal responses. The anal sphincter is more sensitive to the distention of the rectum than that of the proximal colon.

Reproducibility and performance characteristics of colonic compliance, tone, and sensory tests in healthy humans

BACKGROUND

The performance characteristics of colonic sensation and motility measurements are unclear.

AIM

To compare left colon compliance, tone, and sensation in males and females and to evaluate inter and intra-individual coefficients of variation (COV) in these measurements.

METHODS

Data were acquired using standard barostat methods, by one technologist, in 72 human volunteers (38 males, 18-65 years). We measured compliance, fasting tone, and sensation during baseline and post-placebo; postprandial (PP) tone was measured only post-placebo. Compliance and thresholds for first sensation, gas, and pain were measured using ascending method of limits; sensory ratings (0-100 mm VAS) using random phasic distensions at 8-36 mmHg above baseline operating pressure. Change in PP tone was measured by barostat balloon volume for the first 30 min after a 1000-kcal meal. Inter-COV was calculated as 100 (SD/mean), and intra-COV as (100 x SD delta/overall mean).

RESULTS

There were no statistically significant associations with gender for most sensory or motor data at baseline. A modest association of fasting colonic tone and gender was observed. COV are lower (20-35%) for compliance, fasting tone, pain threshold, and sensation ratings than for PP tone and threshold for first or gas sensation (>45%). COV data are similar in males and females; sensation COVs appear smaller in females than in males.

CONCLUSIONS

Testing of compliance, tone and pain, and gas sensation in left colon performs adequately to assess these functions in humans. Lower COV for sensation tests among females is relevant to plan studies of drugs intended for functional GI disorders.

Phenotypic variation of colonic motor functions in chronic constipation

BACKGROUND & AIMS

Colonic motor disturbances in chronic constipation (CC) are heterogeneous and incompletely understood; the relationship between colonic transit and motor activity is unclear. We sought to characterize the phenotypic variability in chronic constipation.

METHODS

Fasting and postprandial colonic tone and phasic activity and pressure-volume relationships were assessed by a barostat manometric assembly in 35 healthy women and 111 women with CC who had normal colon transit (NTC; n = 25), slow transit (STC; n = 19), and defecatory disorders with normal (DD-normal; n = 34) or slow transit (DD-slow; n = 33). Logistic regression models assessed whether motor parameters could discriminate among these groups. Among CC, phenotypes were characterized by principal components analysis of these measurements.

RESULTS

Compared with 10th percentile values in healthy subjects, fasting and/or postprandial colonic tone and/or compliance were reduced in 40% with NTC, 47% with STC, 53% with DD-normal, and 42% with DD-slow transit. Compared with healthy subjects, compliance was reduced (P <or= .05) in isolated STC and DD but not in NTC. Four principal components accounted for 85% of the total variation among patients: factors 1 and 2 were predominantly weighted by fasting and postprandial colonic phasic activity and tone, respectively; factor 3 by postprandial high-amplitude propagated contractions; and factor 4 by postprandial tonic response.

CONCLUSIONS

Fasting and/or postprandial colonic tone are reduced, reflecting motor dysfunctions, even in NTC. Colonic motor assessments allow chronic constipation to be characterized into phenotypes. Further studies are needed to evaluate the relationship among these phenotypes, enteric neuropathology, and response to treatment in CC.

Altered rectal sensory response induced by balloon distention in patients with functional abdominal pain syndrome

Background

Functional abdominal pain syndrome (FAPS) has chronic unexplained abdominal pain and is similar to the psychiatric diagnosis of somatoform pain disorder. A patient with irritable bowel syndrome (IBS) also has chronic unexplained abdominal pain, and rectal hypersensitivity is observed in a majority of the patients. However, no reports have evaluated the visceral sensory function of FAPS precisely. We aimed to test the hypothesis that FAPS would show altered visceral sensation compared to healthy controls or IBS. The present study determined the rectal perceptual threshold, intensity of sensation using visual analogue scale (VAS), and rectal compliance in response to rectal balloon distention by a barostat in FAPS, IBS, and healthy controls.

Methods

First, the ramp distention of 40 ml/min was induced and the thresholds of discomfort, pain, and maximum tolerance (mmHg) were measured. Next, three phasic distentions (60-sec duration separated by 30-sec intervals) of 10, 15 and 20 mmHg were randomly loaded. The subjects were asked to mark the VAS in reference to subjective intensity of sensation immediately after each distention. A pressure-volume relationship was determined by plotting corresponding pressures and volumes during ramp distention, and the compliance was calculated over the linear part of the curve by calculating from the slope of the curve using simple regression.

Results

Rectal thresholds were significantly reduced in IBS but not in FAPS. The VAS ratings of intensity induced by phasic distention (around the discomfort threshold of the controls) were increased in IBS but significantly decreased in FAPS. Rectal compliance was reduced in IBS but not in FAPS.

Conclusion

An inconsistency of visceral sensitivity between lower and higher pressure distention might be a key feature for understanding the pathogenesis of FAPS.

Estrogen altered visceromotor reflex and P2X(3) mRNA expression in a rat model of colitis

P2X(3) and P2X(2/3) receptors are expressed in peripheral tissues and dorsal root ganglia (DRG) and participate in peripheral pain. However, the mechanisms underlying P2X receptor-mediated nociception at different ovarial hormone levels has not been examined. In this study, 24 female rats were randomly divided into sham-operated (sham), ovariectomized (OVX), estrogen-treated, and estrogen-progesterone-treated groups with colitis. In each group, the visceromotor reflex (VMR) to colorectal distension was tested and the DRG were harvested for a real-time PCR analysis of P2X(3) and P2X(2) receptor mRNA. In OVX rats with colitis we found that the VMR to colorectal distension and P2X(3) receptor mRNA in DRG were both significantly decreased. Estrogen replacement reversed the decrease. However, neither the VMR nor the P2X(3) mRNA level in DRG from OVX colitis rats was reversed by the complex of estrogen and progesterone. Patch-clamp recording showed that in colitis rats, estradiol rapidly potentiated the sustained and transient currents evoked by ATP to 336+/-49% and 122+/-12% of controls, respectively, in a subpopulation of DRG neurons, which were blocked by ICI 182, 780, an antagonist of the estrogen receptor. Whereas progesterone rapidly inhibited the transient currents induced by ATP to 67+/-10% of control and had no effect on the sustained currents evoked by the same agonist. These results indicate that P2X(3) receptors are likely to be an important contributor to the altered colonic functions in colitis rats, where the underlying mechanisms are closely related to endogenous estrogen modulation.

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.

Rectal visceral sensitivity in women with irritable bowel syndrome without psychiatric comorbidity compared with healthy volunteers

Background. Psychiatric comorbidity and visceral hypersensitivity are common in patients with irritable bowel syndrome (IBS), but little is known about visceral sensitivity in IBS patients without psychiatric disorders. Aim. We wanted to examine rectal visceral sensitivity in IBS patients without comorbid psychiatric disorders, IBS patients with phobic anxiety and healthy volunteers. Methods. A total of thirty-eight female, non-constipated IBS patients without psychiatric disorders and eleven female IBS patients with phobic anxiety were compared to nine healthy women using a barostat double random staircase method. The non-psychiatric patients were divided into those with diarrhoea predominant symptoms and those with alternating stool habits. Results. The IBS patients without psychiatric disorders had normal visceral pressure thresholds. However, in the diarrhoea predominant subgroup, the volume discomfort threshold was reduced while it was unchanged in those with alternating stool habits. The phobic IBS patients had similar thresholds to the healthy volunteers. The rectal tone was increased in the non-psychiatric IBS patients with diarrhoea predominant symptoms and in the IBS patients with phobic anxiety. Conclusions. Non-constipated IBS patients without psychiatric disorders had increased visceral sensitivity regarding volume thresholds but normal pressure thresholds. Our study suggests that the lowered volume threshold was due to increased rectal tone.

Contributions of pain sensitivity and colonic motility to IBS symptom severity and predominant bowel habits

OBJECTIVES

Irritable bowel syndrome (IBS) patients show pain hypersensitivity and hypercontractility in response to colonic or rectal distention. Aims were to determine whether predominant bowel habits and IBS symptom severity are related to pain sensitivity, colon motility, or smooth muscle tone.

METHODS

One hundred twenty-nine patients classified as IBS with diarrhea (IBS-D, N = 44), IBS with constipation (IBS-C, N = 29), mixed IBS (IBS-M, N = 45), and unspecified IBS (IBS-U, N = 11) based on stool consistency, and 30 healthy controls (HC) were studied. A manometric catheter containing a 600-mL capacity plastic bag was positioned in the descending colon. Pain threshold was assessed using a barostat. Motility was assessed for 10 min with the bag minimally inflated (individual operating pressure [IOP]), 10 min at 20 mmHg above the IOP, and for 15-min recovery following bag inflation. Motility was also recorded for 30 min following an 810-kcal meal.

RESULTS

Compared with HC, IBS patients had lower pain thresholds (medians 30 vs 40 mmHg, P < 0.01), but IBS subtypes were not different. IBS symptom severity was correlated with pain thresholds (rho =-0.36, P < 0.001). During distention, the motility index (MI) was significantly higher in IBS compared with HC (909 +/- 73 vs 563 +/- 78, P < 0.01). Average barostat bag volume at baseline was higher (muscle tone lower) in HC compared with IBS-D and IBS-M but not compared with IBS-C. The baseline MI and bag volume differed between IBS-D and IBS-C and correlated with symptoms of abdominal distention and dissatisfaction with bowel movements. Pain thresholds and MI during distention were uncorrelated.

CONCLUSIONS

Pain sensitivity and colon motility are independent factors contributing to IBS symptoms. Treatment may need to address both, and to be specific to predominant bowel habit.

Impact of depressive symptoms on visceral sensitivity among patients with different subtypes of irritable bowel syndrome

The etiology of irritable bowel syndrome (IBS) is complex and multifaceted. Psychosocial factors play a role in such a process. Several reports suggest that IBS patients have increased psychopathology scores as compared with population controls. The influence of depressive symptoms on rectal sensitivity thresholds vary across different studies. The influence of predominant bowel habits on rectal sensitivity thresholds as determined by barostat-based investigations is not well established. The present report aimed to investigate the influence of depressive symptoms on rectal sensitivity in different subtypes of IBS patients (diarrhea/constipation-predominant vs. alternating subtypes). Depressive symptoms correlated well with first pain sensitivity threshold in alternating patients (n = 8; [rho] = -0.77; p = 0.02) but not in diarrhea/constipation predominant symptoms (n = 11; [rho] = -0.44; p = 0.27). These data suggest that depressive symptoms might impact pain thresholds differently according to the subtype of IBS.

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.

Neurophysiological testing in anorectal disorders

Neurophysiological tests of anorectal function can provide useful information regarding the integrity of neuronal innervation, as well as neuromuscular function. This information can give insights regarding the pathophysiological mechanisms that lead to several disorders of anorectal function, particularly fecal incontinence, pelvic floor disorders and dyssynergic defecation. Currently, several tests are available for the neurophysiological evaluation of anorectal function. These tests are mostly performed on patients referred to tertiary care centers, either following negative evaluations or when there is lack of response to conventional therapy. Judicious use of these tests can reveal significant and new understanding of the underlying mechanism(s) that could pave the way for better management of these disorders. In addition, these techniques are complementary to other modalities of investigation, such as pelvic floor imaging. The most commonly performed neurophysiological tests, along with their indications and clinical utility are discussed. Several novel techniques are evolving that may reveal new information on brain-gut interactions.

Compliance and capacity of the normal human rectum--physical considerations and measurement pitfalls

The assessment of parameters which adequately represent rectal and neorectal compliance is complex. Biological properties of the rectum during distension and relaxation show significant departures from in vitro physical compliance measurements; as much dependent upon the viscoelastic charateristics of hollow organ deformation as upon the technique of compliance calculation. This review discusses the pressure/volume characteristics of importance in the rectum during distension from a bioengineering perspective and outlines the disparities of such measurements in living biological systems. Techniques and pitfalls of newer methods to assess rectal wall stiffness (impedance planimetry and barostat measurement) are discussed.

Effects of sibutramine on gastric emptying, intestinal motility and rectal tone in dogs

The aim of this study was to evaluate the effects of sibutramine on gastric emptying, small-bowel contractions, rectal tone and compliance, and gastrointestinal myoelectrical activity. The study was performed in 14 dogs. It was composed of three separate experiments: gastric emptying of liquids and gastrointestinal slow waves; small-bowel contractions; and rectal tone and rectal compliance. Each experiment included two sessions: a control session and a treatment session with sibutramine (5 mg/kg orally) administrated 2 h before the study. Sibutramine significantly accelerated liquid gastric emptying at 75 and 90 min after the meal but did not alter gastrointestinal slow waves. Gastric emptying at 75 and 90 min was 61.42 +/- 7.71 and 66.32 +/- 7.67% in the control session, and increased to 71.27 +/- 5.14 and 75.93 +/- 5.29% in the session with sibutramine (p < 0.05, vs. control). Sibutramine significantly inhibited postprandial small-bowel contractions. Sibutramine did not alter the rectal tone, but significantly increased rectal compliance. Sibutramine accelerates gastric emptying of liquids but inhibits small-bowel contractions. These findings suggest the peripheral mechanisms of sibutramine in reducing food intake and causing weight loss in obesity patients.

Lipid-induced colonic hypersensitivity in the irritable bowel syndrome: the role of bowel habit, sex, and psychologic factors

BACKGROUND & AIMS

Duodenal lipid infusion increases colonic hypersensitivity in irritable bowel syndrome (IBS). Whether this is affected by bowel habit, psychologic factors, or sex is unknown.

METHODS

We included 61 patients with IBS (50 women, 11 men), 25 with diarrhea-predominant IBS, 17 with constipation-predominant IBS, 19 with alternating-type IBS, and 20 healthy controls (15 women, 5 men). A colonic distension trial was performed with a barostat before and after a 1-hour duodenal lipid infusion (3 kcal/min). Colonic thresholds, colonic tone, and the viscerosomatic referral pattern were assessed and compared between groups. Patients also completed the Hospital Anxiety and Depression scale.

RESULTS

The reduction in colonic pressure thresholds after vs before duodenal lipids was greater in patients than in controls for discomfort (P = .006) and pain (P < .0001). An increased viscerosomatic referral area for pain and discomfort during colonic distensions after vs before duodenal lipids was observed in patients but not in controls. The response was similar in IBS subgroups based on the predominant bowel habit, in patients with vs without anxiety and/or depression, and in women and men with IBS. The colonic tone response during lipid infusion was similar in IBS patients and controls, and in the different IBS subgroups.

CONCLUSIONS

IBS patients show increased colonic sensitivity and altered viscerosomatic referral pattern after duodenal lipids. This response is largely unaffected by the predominant bowel habit, psychologic factors, or sex, but seems to be related to IBS per se.

Enteroendocrine cell counts correlate with visceral hypersensitivity in patients with diarrhoea-predominant irritable bowel syndrome

The objective of this study was to determine whether or not the number of enteroendocrine cells (ECs) in the gut is related to visceral hypersensitivity in patients with diarrhoea-predominant irritable bowel syndrome (D-IBS). Twenty-five subjects with D-IBS (mean, 43.1 years; 16 women, nine men) were recruited into our study, along with 13 healthy controls (mean, 40.7 years; nine women, four men). Maximally tolerable pressures were evaluated via barostat testing, and the levels of ECs were immunohistochemically identified and quantified via image analysis. The numbers of ECs between the D-IBS subjects and the controls were not significantly different in the terminal ileum, ascending colon and rectum. However, the maximally tolerable pressures determined in the D-IBS subjects were significantly lower than those of the control subjects (P < 0.01), and we detected a significant relationship between the maximally tolerable pressures and the numbers of ECs in the rectum (r = -0.37, P < 0.01). Rectal sensitivity was enhanced to a greater degree in D-IBS patients exhibiting an elevated level of rectal ECs. This study provides some evidence to suggest that ECs play an important role in visceral hypersensitivity.

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.

Rectal hyposensitivity

Rectal hyposensitivity (RH) relates to a diminished perception of rectal distension that is diagnosed during anorectal physiologic investigation. There have been few direct studies of this physiologic abnormality, and its contribution to the development of functional bowel disorders has been relatively neglected. However, it appears to be common in patients with such disorders, being most prevalent in patients with functional constipation with or without fecal incontinence. Indeed, it may be important in the etiology of symptoms in certain patients, given that it is the only "apparent" identifiable abnormality on physiologic testing. Currently, it is usually diagnosed on the basis of elevated sensory threshold volumes during balloon distension in clinical practice, although such a diagnosis may be susceptible to misinterpretation in the presence of altered rectal wall properties, and thus it is uncertain whether a diagnosis of RH reflects true impairment of afferent nerve function. Furthermore, the etiology of RH is unclear, although there is limited evidence to support the role of pelvic nerve injury and abnormal toilet behavior. The optimum treatment of patients with RH is yet to be established. The majority are managed symptomatically, although "sensory-retraining biofeedback" appears to be the most effective treatment, at least in the short term, and is associated with objective improvement in the rectal sensory function. Currently, fundamental questions relating to the contribution of this physiologic abnormality to the development of functional bowel disorders remain unanswered. Acknowledgment of the potential importance of RH is thus required by clinicians and researchers to determine its relevance.

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.

Gender-related differences in visceral perception in health and irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is more common in female subjects, and IBS patients generally exhibit reduced pain thresholds to rectal distension. The aim of the present paper was to determine gender-related differences in rectal perception in both healthy controls and IBS patients.

METHODS

Fifty-nine IBS patients (age 20-65 years; mean, 39.2 years; 31 women, 28 men) with symptoms that fulfilled Rome-II criteria and 21 healthy controls (age 25-58 years; mean, 37.8 years; 11 women, 10 men) were recruited. Participants completed a questionnaire regarding bowel symptoms and psychological distress, and maximal tolerable pressures were evaluated via barostat tests.

RESULTS

Although healthy women appear to have lower perception thresholds than men, significant gender differences in pain sensitivity were not detected (P > 0.05). In addition, female patients with IBS also exhibited no enhanced colorectal perception, as compared with male IBS patients (P > 0.05).

CONCLUSIONS

No gender differences in visceral perception were determined to exist between the healthy controls and the IBS patients. Therefore, the increased prevalence of IBS in women may be related to another set of pathophysiological factors, and not to gender-related differences in visceroperception.

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.

Mucosal mast cell counts correlate with visceral hypersensitivity in patients with diarrhea predominant irritable bowel syndrome

BACKGROUND AND AIM

Although increased mast cells in the gut and their role in visceral hypersensitivity in irritable bowel syndrome have been postulated, this relationship remains unclear. Our aim was to determine whether a relationship exists between the number of mucosal mast cells in the gut and visceral hypersensitivity.

METHOD

Eighteen patients with diarrhea predominant irritable bowel syndrome (D-IBS) (eight females, 10 males aged 25-65 years; mean 42.6 years) with symptoms meeting the Rome-II criteria, and 15 healthy controls (five females, 10 males aged 31-57 years; mean 41.4 years) were recruited. Participants completed a questionnaire for bowel symptoms and psychological distress. Colonic mucosal mast cells were identified immunohistochemically and quantified by image analysis, and maximally tolerable pressures were evaluated using barostat test.

RESULTS

Numbers of mast cells were significantly greater in the terminal ileum, ascending colon and rectum of D-IBS patients compared with controls (P<0.01). A multivariate analysis of the barostat test showed that maximally tolerable pressures of D-IBS patients were significantly lower than those of controls (P<0.01). When patients were divided into the rectal hypersensitivity (+) and (-) groups by the distension level of 34 mmHg, mast cell counts were significantly higher in the rectal hypersensitivity (-) group than in the rectal hypersensitivity (+) group for the terminal ileum, ascending colon and rectum (P<0.05, respectively).

CONCLUSIONS

Rectal sensitivity was enhanced in D-IBS patients with moderately increased mucosal mast cells, but it was attenuated in patients with markedly increased ones. This study might provide evidence for an important role of mast cells in visceral hypersensitivity.

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.

The effects of an acute serotonergic challenge on brain-gut responses in irritable bowel syndrome patients and controls

BACKGROUND

Serotonin, a key denominator of the brain-gut axis is involved in the regulation of gastrointestinal function as well as cognition, mood and hypothalamic-pituitary-adrenal axis-mediated neuroendocrine responses.

AIM

To assess the effects of an acutely increased serotonergic activity, using a 20 mg intravenous citalopram challenge test on visceral perception, affective memory performance, mood and neuroendocrine responses, respectively, in diarrhoea-predominant irritable bowel syndrome patients and controls.

METHODS

In a randomized, double-blind crossover design, 14 diarrhoea-predominant irritable bowel syndrome patients and 14 matched controls were studied under citalopram and placebo conditions, respectively. Visceral perception was scored in response to rectal distensions. Affective memory performance, mood, levels of adrenocorticotropic hormone, cortisol, prolactin and biochemical parameters of serotonergic metabolism were simultaneously assessed.

RESULTS

Visceral perception did not significantly differ between the citalopram and placebo condition. Citalopram administration enhanced affective memory performance because of a bias towards positive material but no significant changes in mood. Citalopram significantly increased plasma serotonin, adrenocorticotropic hormone and cortisol levels compared with placebo. Citalopram did not differentially affect the patient or control group.

CONCLUSIONS

We have provided evidence that acutely increased serotonergic activity influences neuroendocrine responses and cognition in diarrhoea-predominant irritable bowel syndrome and controls without a significant effect on visceral perception.

Attenuation of the colorectal tonic reflex in female patients with irritable bowel syndrome

Alterations in normal intestinointestinal reflexes may be important contributors to the pathophysiology of irritable bowel syndrome (IBS). Our aims were to compare the rectal tonic responses to colonic distension in female IBS patients with predominant constipation (IBS-C) and with predominant diarrhea (IBS-D) to those in healthy females, both fasting and postprandially. Using a dual barostat assembly, 2-min colonic phasic distensions were performed during fasting and postprandially. Rectal tone was recorded before, during, and after the phasic distension. Colonic compliance and colonic sensitivity in response to the distension were also evaluated fasting and postprandially. Eight IBS-C patients, 8 IBS-D patients, and 8 age- and sex-matched healthy subjects (group N) participated. The fasting increments in rectal tone in response to colonic distension in both IBS-C (rectal balloon volume change -4.6 +/- 6.1 ml) and IBS-D (-7.9 +/- 4.9 ml) were significantly reduced compared with group N (-34 +/- 9.7 ml, P = 0.01). Similar findings were observed postprandially (P = 0.02). When adjusted for the colonic compliance of individual subjects, the degree of attenuation in the rectal tonic response in IBS compared with group N was maintained (fasting P = 0.007; postprandial P = 0.03). When adjusted for colonic sensitivity there was a trend for the attenuation in the rectal tonic response in IBS patients compared with group N to be maintained (fasting P = 0.07, postprandial P = 0.08). IBS patients display a definite attenuation of the normal increase in rectal tone in response to colonic distension (colorectal reflex), fasting and postprandially. Alterations in colonic compliance and sensitivity in IBS are not likely to contribute to such attenuation.

Relationship between symptoms and hypersensitivity to rectal distension in patients with irritable bowel syndrome

BACKGROUND

Visceral hypersensitivity is considered an important pathophysiological mechanism in irritable bowel syndrome, yet its relationship to symptoms is unclear.

AIM

To detect possible associations between symptoms and the presence of hypersensitivity to rectal distension in patients with irritable bowel syndrome.

METHODS

Ninety-two irritable bowel syndrome patients and 17 healthy volunteers underwent a rectal barostat study. The association between specific irritable bowel syndrome symptoms and the presence of hypersensitivity was examined using Area under the Receiver Operating Characteristic curves.

RESULTS

Irritable bowel syndrome patients had significantly lower thresholds for discomfort/pain than healthy volunteers: 24 (18-30) and 30 (27-45) mmHg above minimal distending pressure, respectively. Forty-one patients (45%) showed hypersensitivity to rectal distension. Proportions of patients with different predominant bowel habits were similar in hypersensitive and normosensitive subgroups (diarrhoea predominant: 39 and 41%, respectively; alternating type: 27 and 28%, respectively; constipation predominant: 34 and 31%, respectively). Severe abdominal pain was more frequent in hypersensitive, compared with normosensitive patients (88% vs. 67%, P = 0.02), but none of the individual irritable bowel syndrome symptoms could accurately predict the presence of hypersensitivity, as assessed by Area under the Receiver Operating Characteristic curve analysis.

CONCLUSIONS

Hypersensitive and normosensitive irritable bowel syndrome patients present with comparable, heterogeneous symptomatology. Therefore, selection based on clinical parameters is unlikely to discriminate individual irritable bowel syndrome patients with visceral hypersensitivity from those with normal visceral sensitivity.

Rectal intussusception: a study of rectal biomechanics and visceroperception

OBJECTIVES

Rectal intussusception (RI) is a significant cause of morbidity amongst those with a rectal evacuatory disorder. The pathophysiology is unknown, but may involve abnormal biomechanics of the rectal wall similar to that previously demonstrated in patients with overt rectal prolapse (RP). Using an electromechanical barostat, this study aimed to investigate the biomechanics and visceroperception of the rectal wall in patients with RI.

METHODS

Twenty consecutive patients (12 females, median age 46 yr (range 24-66)) with symptomatic, full-thickness RI were studied. Patients underwent assessment of rectal compliance, visceroperception, adaptive response to isobaric distension at urge threshold, and assessment of the postprandial response. Results were compared with those obtained in 28 asymptomatic volunteers, 10 with RI (6 females, median age 29 yr (range 21-36)) and 18 (9 females, median age 33 yr (range 21-62)) without.

RESULTS

In the absence of the clinical finding of solitary rectal ulcer syndrome (SRUS), patients with symptomatic RI have normal rectal wall biomechanics, as do asymptomatic volunteers with RI (p < 0.05). Patients with the clinical finding of SRUS had reduced compliance and adaptation. In all three groups, there was a linear relationship between rectal pressure and visceroperception. The postprandial contractile response was similar between groups.

CONCLUSIONS

Patients with RI have normal rectal wall biomechanics. This is in contrast to patients with RP, and suggests that while they may represent different stages of the same disease process, they are physiologically distinct. In patients with RI and SRUS, rectal wall inflammation and fibrosis, perhaps arising secondary to the intussusception, may explain the physiological changes observed.

Disturbances of motility and visceral hypersensitivity in irritable bowel syndrome: biological markers or epiphenomenon

Motility and visceral hypersentitivity are regarded as the primary mechanisms of symptom development in irritable bowel syndrome(IBS). While a variety of motor abnormalities have been described throughout the gastrointestinal tract in IBS, their specificity and relationship to symptoms remain unclear. Visceral hypersensitivity is ubiquitous in functional gastrointestinal disease and is especially common in IBS. Again, however, its specificity for IBS has been questioned. Many factors, including stress and psychopathology,complicate the interpretation of these phenomena and new re-search suggests that mucosal inflammation and luminal factors may be more fundamental to the etiology of this common disorder.