Towards identifying optimal doses for alpha-2 adrenergic modulation of colonic and rectal motor and sensory function

The Sympathetic-Immune Milieu in Metabolic Health and Diseases: Insights from Pancreas, Liver, Intestine, and Adipose Tissues

Sympathetic innervation plays a crucial role in maintaining energy balance and contributes to metabolic pathophysiology. Recent evidence has begun to uncover the innervation landscape of sympathetic projections and sheds light on their important functions in metabolic activities. Additionally, the immune system has long been studied for its essential roles in metabolic health and diseases. In this review, the aim is to provide an overview of the current research progress on the sympathetic regulation of key metabolic organs, including the pancreas, liver, intestine, and adipose tissues. In particular, efforts are made to highlight the critical roles of the peripheral nervous system and its potential interplay with immune components. Overall, it is hoped to underscore the importance of studying metabolic organs from a comprehensive and interconnected perspective, which will provide valuable insights into the complex mechanisms underlying metabolic regulation and may lead to novel therapeutic strategies for metabolic diseases.

Hypermobile Ehlers-Danlos syndrome and disorders of the gastrointestinal tract: What the gastroenterologist needs to know

BACKGROUND AND AIM

Hypermobile Ehlers-Danlos syndrome (hEDS) and the hypermobility spectrum disorders (HSD) can be challenging to diagnose and manage. Gastrointestinal symptoms and disorders of gut-brain interaction are common in this cohort and multifactorial in origin. The primary aim of this review is to arm the gastroenterologist with a clinically useful understanding of HSD/hEDS, by exploring the association of gastrointestinal disorders with HSD/hEDS, highlighting current pathophysiological understanding and providing a pragmatic approach to managing these patients.

METHODS

Literature relevant to the gastrointestinal system and hypermobile Ehlers-Danlos syndrome was systematically searched, critically appraised, and summarized.

RESULTS

Diagnosis is based upon clinical criteria and a genetic basis is yet to be defined. The prevalence of many gut symptoms, including abdominal pain (69% vs 27%, P < 0.0001), postprandial fullness (34% vs 16%, P = 0.01), constipation (73% vs 16%, P < 0.001), and diarrhea (47% vs 9%, P < 0.001) are significantly higher in HSD/hEDS compared with non-HSD/hEDS individuals. Disorders of gut-brain interaction are also common, particularly functional dyspepsia. The pathophysiology of gut symptoms is poorly understood but may involve effects of connective tissue laxity and its functional consequences, and the influence of autonomic dysfunction, medication and comorbid mental health disorders. Awareness is the key to early diagnosis. Management is limited in evidence-base but ideally should include an integrated multidisciplinary approach.

CONCLUSIONS

HSD/hEDS is a multisystemic disorder in which gastrointestinal symptoms, particularly related to disorders of gut-brain interaction are common. Deficiencies in knowledge regarding the pathophysiological processes limit evidence-based interventions and remain important areas for future research.

Current perspectives on the diagnosis and management of functional anorectal disorders in patients with inflammatory bowel disease

Despite advances in inflammatory bowel disease (IBD) therapies, a significant proportion of patients with quiescent disease experience persistent, debilitating symptoms of faecal incontinence (FI), urgency and defaecatory disorders due to anorectal dysfunction. Such symptoms are often underreported or misdiagnosed and can lead to potentially premature treatment 'escalation' and under-utilisation of pelvic floor investigations. In this review article, we consider putative pathophysiological post-inflammatory changes resulting in altered anorectal sensitivity, motility and neuromuscular coordination and how this may drive symptoms in quiescent IBD. Finally, we discuss a pragmatic approach to investigating and managing anorectal dysfunction and highlight areas for future research for this often-neglected group of patients.

A pharmacological challenge predicts reversible rectal sensorimotor dysfunctions in women with fecal incontinence

BACKGROUND

In order to understand the pathophysiology of rectal sensorimotor dysfunctions in women with fecal incontinence (FI) and rectal urgency, we evaluated the effects of a muscarinic antagonist and an adrenergic α₂ agonist on these parameters.

METHODS

Firstly, rectal distensibility and sensation were evaluated with a barostat and sinusoidal oscillation at baseline and after randomization to intravenous saline or atropine in 16 healthy controls and 44 FI patients. Thereafter, FI patients were randomized to placebo or clonidine for 4 wk; rectal compliance and sensation were revaluated thereafter. The effect of atropine and clonidine on rectal functions and the relationship between them were evaluated.

RESULTS

At baseline, compared to controls, rectal capacity was lower (P = .03) while the mean pressure (P = .02) and elastance (P = .01) during sinusoidal oscillation were greater, signifying reduced distensibility, in FI. Compared to placebo, atropine increased (P ≤ .02) the heart rate in controls and FI and reduced (P = .03) the variability in rectal pressures during sinusoidal oscillation in controls. Clonidine increased rectal compliance (P = .04) and reduced rectal capacity (P = .03) in FI. The effects of atropine and clonidine on compliance (r = .44, P = .003), capacity (r = .34, P = .02), pressures during sinusoidal oscillation (r = .3, P = .057), pressure (r = .6, P < .0001), and volume sensory thresholds (r = .48, P = .003) were correlated.

CONCLUSIONS

The effects of atropine and clonidine on rectal distensibility and sensation were significantly correlated. A preserved response to atropine suggests that reduced rectal distensibility is partly reversible, mediated by cholinergic mechanisms, and may predict the response to clonidine, providing a pharmacological challenge.

Pharmacological modulation of colorectal distension evoked potentials in conscious rats

BACKGROUND

Cerebral evoked potentials (CEP) induced by colorectal distension (CRD) in conscious rats provides a novel method in studies of visceral sensitivity. The aim of this study was to explore the pharmacological effect on CEP of compounds known to reduce the visceromotor response to CRD.

METHODS

Epidural electrodes were chronically implanted in eight female Sprague-Dawley rats. Evoked potentials were elicited by colorectal rapid balloon distensions (100 ms, 80 mmHg) and the effect of WIN55 (cannabinoid CB receptor agonist), clonidine (adrenergic α₂ receptor agonist), MPEP (mGluR5 receptor antagonist), pregabalin (ligand of α₂δ subunits in voltage-gated calcium channels) and baclofen (GABA-B receptor agonist) on amplitudes and latency of CEP were determined.

RESULTS

WIN55 (0.1 μmol kg^-1), clonidine (0.05 μmol kg^-1), MPEP (10 μmol kg^-1) and pregabalin (200 μmol kg^-1) caused a significant, p < 0.05, reduction of the N2 to P2 peak-to-peak amplitude by 23 ± 8%, 25 ± 8%, 39 ± 5%, and 47 ± 6% respectively. Baclofen (9 μmol kg^-1) induced a prolongation of the N2 peak latency of 18 ± 4% but had no significant effect on the amplitudes.

CONCLUSION

The obtained results suggest that MPEP, WIN55, clonidine, and pregabalin reduce visceral nociceptive input to the brain, whereas the lack of effect of baclofen on CRD evoked CEP amplitudes suggest that the effect on VMR is not due to a direct analgesic effect. Brain responses to colorectal distension provide a useful tool to evaluate pharmacological effects in rats and may serve as a valuable preclinical model for understanding pharmacological mechanisms related to visceral sensitivity.

What about clonidine for diarrhoea? A systematic review and meta-analysis of its effect in humans

BACKGROUND

Clonidine is considered an alternative treatment for refractory diarrhoea. The evidence in the literature is scarce and not conclusive. The present paper's purpose is to gather available evidence and provide a systematic answer regarding the effectiveness of clonidine for diarrhoea.

METHOD

We performed a systematic review of clonidine and its effect on diarrhoea. Meta-analysis was performed with a random effects model of the standardized mean difference (SMD) or the weighted mean difference and heterogeneity was quantified with I (2) and publication bias was assessed with Egger's and Begg's test. Subgroup analyses and meta-regression were performed to investigate sources of heterogeneity. Any empirical study describing use of clonidine for diarrhoea in humans independent of age was included. For the meta-analysis, papers had to provide sufficient data to produce an effect measure, while case reports were not included in the meta-analysis and are discussed narratively only.

RESULTS

A total of 24 trials and seven case reports were identified. Clonidine (median dose 300 μg/day) has been used for treatment of diarrhoea in irritable bowel syndrome, faecal incontinence, diabetes, withdrawal-associated diarrhoea, intestinal failure, neuroendocrine tumours and cholera; studies were also performed on healthy volunteers. Results indicate a strong effect of clonidine on diarrhoea (SMD = -1.02, 95% confidence interval [CI] -1.46 to -0.58) with a decrease of stool volume by 0.97 l/day, stool frequency by 0.4 times/day and increase in transit time by 31 minutes. In a sensitivity analysis of studies with functional diarrhoea and sample size over 10 subjects, the effect was similar -0.99 (95% CI -1.54 to -0.43). There is however significant heterogeneity and publication bias. Heterogeneity decreased in subgroup analyses by condition but not with other factors examined. A limitation of the present study includes small study effects.

CONCLUSION

Clonidine is effective for treatment of diarrhoea and should be considered as an alternative when all other medications have failed.

Potential Causes and Present Pharmacotherapy of Irritable Bowel Syndrome: An Overview

BACKGROUND

Irritable bowel syndrome (IBS) is currently one of the most common disorders of the digestive system in the Western society. Almost 2 out of 10 people suffer from IBS with women being more affected than men. IBS is associated with abdominal pain, bloating and altered stool consistency and imposes a heavy burden for the affected patients.

SUMMARY

The pathophysiology of IBS remains elusive although potential causes have been suggested, such as a deranged brain-gut signaling, hypersensitivity of visceral sensory afferent fibers, bacterial gastroenteritis, small intestinal bacterial overgrowth (SIBO), genetic alterations and food sensitivity. Targets for the pharmacotherapy of IBS include the serotonergic and opioidergic system, and the microbial population of the gut. Alternative therapies like traditional Chinese medicine have shown some success in the combat against IBS. Key Messages: Many therapeutics for the treatment of IBS have emerged in the past; however, only a few have met up with the expectations in larger clinical trials. Additionally, the multifactorial etiology of IBS and its variety of cardinal symptoms requires an individual set of therapeutics. This review provides a short overview of potential causes and current pharmacological therapeutics and of additional and alternative therapies for IBS.

Involvement of α2-adrenoceptors in inhibitory and facilitatory pain modulation processes

BACKGROUND

In healthy humans, high-frequency electrical stimulation (HFS) of the forearm not only produces hyperalgesia at the site of stimulation but also reduces sensitivity to pressure-pain on the ipsilateral side of the forehead. In addition, HFS augments the ipsilateral trigeminal nociceptive blink reflex and intensifies the ipsilateral component of conditioned pain modulation. The aim of this study was to determine whether α2-adrenoceptors mediate these ipsilateral nociceptive influences.

METHODS

The α2-adrenoceptor antagonist yohimbine was administered to 22 participants in a double-blind, placebo-controlled crossover study. In each session, thermal and mechanical sensitivity in the forearms and forehead was assessed before and after HFS. In addition, the combined effect of HFS and yohimbine on the nociceptive blink reflex and on conditioned pain modulation was explored. In this paradigm, the conditioning stimulus was cold pain in the ipsilateral or contralateral temple, and the test stimulus was electrically evoked pain in the forearm.

RESULTS

Blood pressure and electrodermal activity increased for several hours after yohimbine administration, consistent with blockade of central α2-adrenoceptors. Yohimbine not only augmented the nociceptive blink reflex ipsilateral to HFS but also intensified the inhibitory influence of ipsilateral temple cooling on electrically evoked pain at the HFS-treated site in the forearm. Yohimbine had no consistent effect on primary or secondary hyperalgesia in the forearm or on pressure-pain in the ipsilateral forehead.

CONCLUSIONS

These findings imply involvement of α2-adrenoceptors both in ipsilateral antinociceptive and pronociceptive pain modulation processes. However, a mechanism not involving α2-adrenoceptors appears to mediate analgesia in the ipsilateral forehead after HFS.

Current management of fecal incontinence

OBJECTIVE

To review the management of fecal incontinence, which affects more than 1 in 10 people and can have a substantial negative impact on quality of life.

METHODS

The medical literature between 1980 and April 2012 was reviewed for the evaluation and management of fecal incontinence.

RESULTS

A comprehensive history and physical examination are required to help understand the severity and type of symptoms and the cause of incontinence. Treatment options range from medical therapy and minimally invasive interventions to more invasive procedures with varying degrees of morbidity. The treatment approach must be tailored to each patient. Many patients can have substantial improvement in symptoms with dietary management and biofeedback therapy. For younger patients with large sphincter defects, sphincter repair can be helpful. For patients in whom biofeedback has failed, other options include injectable medications, radiofrequency ablation, or sacral nerve stimulation. Patients with postdefecation fecal incontinence and a rectocele can benefit from rectocele repair. An artificial bowel sphincter is reserved for patients with more severe fecal incontinence.

CONCLUSION

The treatment algorithm for fecal incontinence will continue to evolve as additional data become available on newer technologies.

Dual effects of α2 -adrenoceptors in modulating myogenic tone in sheep isolated internal anal sphincter

BACKGROUND

The role of α-adrenoceptors in promoting continence through modulation of sphincter tone has focused primarily on the effects of α1 -adrenoceptors. We have used three clinically available agents, which are selective for α2 -adrenoceptors, to investigate their role in contractile and neurogenic responses on the internal anal sphincter (IAS).

METHODS

IAS strips, which had spontaneously generated tone, were used to investigate the contractile effect of lofexidine, brimonidine, and dexmedetomidine on muscle tone in the presence or absence of subtype selective antagonists. The effect of brimonidine on the magnitude and time course of neurogenic responses generated by electrical field stimulation (EFS) was also examined. The affinity of test compounds at α1 - and α2 -adrenoceptors was established by competition binding with [3H]-prazosin and [3H]-RX821002.

KEY RESULTS

All agonists caused concentration-dependent contraction of the IAS and lofexidine demonstrated an enantiomeric difference in potency with a 10-fold difference between the (-) and (+) isomers. Responses to lofexidine and dexmedetomidine were inhibited in the presence of the α1 -adrenoceptor selective antagonist prazosin, but not in the presence of RX811059 (α2 -adrenoceptor selective antagonist); brimonidine responses were inhibited by RX811059 and, to a lesser extent, by prazosin. Brimonidine affected both magnitude and duration of neurogenic responses, which was reversed in the presence of RX811059.

CONCLUSIONS & INFERENCES

We conclude that α2 -adrenoceptors can mediate contraction of IAS, although this effect is most evident with efficacious imidazoline agonists rather than the most selective ligand. In addition, this receptor subtype can directly inhibit noradrenergic contractile responses to EFS and, indirectly, enhance nitrergic relaxatory responses.

Effects of clonidine in women with fecal incontinence

BACKGROUND & AIMS

Some women with urge-predominant fecal incontinence (FI) have diarrhea-predominant irritable bowel syndrome and a stiffer and hypersensitive rectum. We evaluated the effects of the α2-adrenergic agonist clonidine on symptoms and anorectal functions in women with FI in a prospective, placebo-controlled trial.

METHODS

We assessed bowel symptoms and anorectal functions (anal pressures, rectal compliance, and sensation) in 43 women (age, 58 ± 2 y) with urge-predominant FI, randomly assigned to groups given oral clonidine (0.1 mg, twice daily) or placebo for 4 weeks. Before and after administration of the medication, anal pressures were evaluated by manometry, and rectal compliance and sensation were measured using a barostat. Anal sphincter injury was evaluated by endoanal magnetic resonance imaging. Bowel symptoms were recorded in daily and weekly diaries. The primary end point was the FI and Constipation Assessment symptom severity score.

RESULTS

FI scores decreased from 9.1 ± 0.3 to 7.6 ± 0.5 among subjects given placebo and from 8.1 ± 0.4 to 6.5 ± 0.6 among patients given clonidine. Clonidine did not affect FI symptom severity, bowel symptoms (stool consistency or frequency), anal pressures, rectal compliance, or sensation compared with placebo. However, when baseline data were used to categorize subjects as those with or without diarrhea, clonidine reduced the proportion of loose stools in patients with diarrhea only (P = .018). Clonidine also reduced the proportion of days with FI in patients with diarrhea (P = .0825).

CONCLUSIONS

Overall, clonidine did not affect bowel symptoms, fecal continence, or anorectal functions, compared with placebo, in women with urge-predominant FI. Among patients with diarrhea, clonidine increased stool consistency, with a borderline significant improvement in fecal continence. ClinicalTrials.gov, Number NCT00884832.

Irritable bowel syndrome: The evolution of multi-dimensional looking and multidisciplinary treatments

Irritable bowel syndrome (IBS) is common in the society. Among the putative pathogeneses, gut dysmotility results in pain and disturbed defecation. The latter is probably caused by the effect of abnormal gut water secretion. The interaction between abnormal gas accumulation, abdominal pain and bloating remains controversial. Visceral hypersensitivity and its modification along with the central transmission are the characteristics of IBS patients. The identification of biologic markers based on genetic polymorphisms is undetermined. Imbalanced gut microbiota may alter epithelial permeability to activate nociceptive sensory pathways which in turn lead to IBS. Certain food constituents may exacerbate bowel symptoms. The impact of adult and childhood abuses on IBS is underestimated. Using the concept of biopsychosocial dysfunction can integrate multidimensional pathogeneses. Antispasmodics plus stool consistency modifiers to treat the major symptoms and defecation are the first-line drug treatment. New drugs targeting receptors governing bowel motility, sensation and secretion can be considered, but clinicians must be aware of their potential serious side effects. Psychiatric drugs and modalities may be the final options for treating intractable subjects. Probiotics of multi-species preparations are safe and worth to be considered for the treatment. Antibiotics are promising but their long-term safety and effectiveness are unknown. Diet therapy including exclusion of certain food constituents is an economic measure. Using relatively safe complementary and alternative medicines (CAMs) may be optional to those patients who failed classical treatment. In conclusion, IBS is a heterogeneous disorder with multidimensional pathogeneses. Personalized medicines with multidisciplinary approaches using different classes of drugs, psychiatric measures, probiotics and antibiotics, dietary therapy, and finally CAMs, can be considered.

Drug development for the irritable bowel syndrome: current challenges and future perspectives

Medications are frequently used for the treatment of patients with the irritable bowel syndrome (IBS), although their actual benefit is often debated. In fact, the recent progress in our understanding of the pathophysiology of IBS, accompanied by a large number of preclinical and clinical studies of new drugs, has not been matched by a significant improvement of the armamentarium of medications available to treat IBS. The aim of this review is to outline the current challenges in drug development for IBS, taking advantage of what we have learnt through the Rome process (Rome I, Rome II, and Rome III). The key questions that will be addressed are: (a) do we still believe in the "magic bullet," i.e., a very selective drug displaying a single receptor mechanism capable of controlling IBS symptoms? (b) IBS is a "functional disorder" where complex neuroimmune and brain-gut interactions occur and minimal inflammation is often documented: do we need to target gut motility, visceral sensitivity, or minimal inflammation? (c) are there validated biomarkers (accepted by regulatory agencies) for studies of sensation and motility with experimental medications in humans? (d) do animal models have predictive and translational value? (e) in the era of personalized medicine, does pharmacogenomics applied to these medications already play a role? Finally, this review will briefly outline medications currently used or in development for IBS. It is anticipated that a more focused interaction between basic science investigators, pharmacologists, and clinicians will lead to better treatment of IBS.

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.

The effects of clonidine on symptoms and anorectal sensorimotor function in women with faecal incontinence

BACKGROUND

Women with faecal incontinence and rectal urgency have increased rectal stiffness and sensation.

AIM

To evaluate the effects of clonidine, an alpha(2) -adrenergic agonist, in faecal incontinence.

METHODS

In this open-label uncontrolled study, bowel symptoms and anorectal functions (anal pressures, rectal compliance, and sensation) were assessed before and during treatment with transdermal clonidine (0.2 mg daily, 4 weeks) in 12 women with urge-predominant faecal incontinence.

RESULTS

Clonidine reduced the frequency (17.8 +/- 3.1 before vs. 8.8 +/- 3.9 after, P = 0.03) and number of days with faecal incontinence (11.8 +/- 1.6 before vs. 6.1 +/- 1.8 after, P = 0.02), faecal incontinence symptom severity score (max = 13, 8.3 +/- 0.7 vs. 5.6 +/- 0.9, P < 0.01), and allowed patients to defer defecation for a longer duration (P = 0.03). Although overall effects on anorectal functions were not significant, the treatment-associated reduction in faecal incontinence episodes was associated with increased rectal compliance (r = -0.58, P < 0.05) and reduced rectal sensation. (r = -0.73, P = 0.007 vs. desire to defecate pressure threshold).

CONCLUSIONS

Clonidine improves symptoms in women with faecal incontinence; this improvement is associated with increased rectal compliance and reduced rectal sensitivity. A controlled study is necessary to confirm these observations.

Current and novel therapeutic options for irritable bowel syndrome management

Irritable bowel syndrome is a functional gastrointestinal disorder affecting up to 3-15% of the general population in western countries. It is characterised by unexplained abdominal pain, discomfort, and bloating in association with altered bowel habits. The pathophysiology of irritable bowel syndrome is multifactorial involving disturbances of the brain-gut axis. The pathophysiology provides the rationale for pharmacotherapy: abnormal gastrointestinal motor functions, visceral hypersensitivity, psychosocial factors, autonomic dysfunction, and mucosal immune activation. Understanding the mechanisms, and their mediators or modulators including neurotransmitters and receptors have led to several therapeutic approaches including agents acting on the serotonin receptor or serotonin transporter system, antidepressants, novel selective anticholinergics, alpha-adrenergic agonists, opioid agents, cholecystokinin-antagonists, neurokinin-antagonists, somatostatin receptor agonists, corticotropin releasing factor antagonists, chloride channel activators, guanylate cyclase-c agonists, melatonin, atypical benzodiazepines, antibiotics, immune modulators and probiotics. The mechanisms and current evidence regarding efficacy of these agents are reviewed.

The antinociceptive effects of intravenous dexmedetomidine in colorectal distension-induced visceral pain in rats: the role of opioid receptors

BACKGROUND

In comparison with cutaneous pain, the role of alpha(2)-adrenoceptor (alpha(2)-AR) agonists in visceral pain has not been extensively examined. We aimed to characterize the antinociceptive effect of IV dexmedetomidine on visceral pain in rats and to determine whether antinociception thus produced is mediated by opioid receptors.

METHODS

Male Sprague Dawley rats (250-300 g) were instrumented with a venous catheter for drug administration and with enameled nichrome electrodes for electromyography of the external oblique muscles. Colorectal distension (CRD) was used as the noxious visceral stimulus, and the visceromotor response to CRD was quantified electromyographically before and 5, 15, 30, 60, 90, and 120 min after dexmedetomidine or clonidine administration. Antagonists were administered 10 min before dexmedetomidine. After confirmation of normal distribution of data, one-way analysis of variance with the Tukey-Kramer post hoc test was used for multiple comparison.

RESULTS

IV administration of dexmedetomidine (2.5-20 microg/kg) and clonidine (10-80 microg/kg) produced a dose-dependent reduction in visceromotor response with 50% effective dose values of 10.5 and 37.6 microg/kg, respectively. Administration of the nonspecific alpha(2)-AR antagonist yohimbine (1 mg/kg), but not the peripherally restricted alpha(2)-AR antagonist MK-467 (1 mg/kg), abolished the antinociceptive effect of dexmedetomidine (10 microg/kg). In addition, inhibition of opioid receptors by naloxone (1 mg/kg) attenuated the antinociceptive effect of dexmedetomidine.

CONCLUSION

Our data indicate that IV dexmedetomidine exerts pronounced antinociception against CRD-induced visceral pain and suggest that the antinociceptive effect of dexmedotimidine is mediated in part by opioid receptors, but peripheral alpha(2)-ARs are not involved.

Colorectal responses to distension and feeding in patients with spinal cord injury

The role of the central nervous system in enteroenteric motor reflexes remains controversial. Our aims were as follows: 1) to evaluate colorectal, rectocolic, gastrocolonic, and gastrorectal reflex responses in patients with cervical spinal cord injury (SCI) and 2) to compare these responses with those in healthy subjects. In six patients with SCI (5 male, 42 +/- 4 yr) and six healthy control subjects (5 male, 36 +/- 5 yr), 2-min phasic distensions were performed randomly via dual-barostat balloons in the colon and rectum. Continuous colonic and rectal balloon volumes were recorded during distensions and after a 1,000-kcal liquid meal. Mean balloon volumes were recorded before, during, and after phasic distensions and over 60 min postprandially. The colorectal response was similar in control subjects and SCI patients (rectal volume reduction = 28 +/- 11% and 15 +/- 5% in SCI patients and healthy subjects, respectively); the rectocolic response was variable. The gastrocolonic response was present in all subjects (colonic volume reduction = 49 +/- 4% and 44 +/- 3% in SCI patients and healthy subjects, respectively), with a time effect in the first 30 min (P < 0.0001) and a group effect in the second 30 min (P < 0.004). The gastrorectal response was present in four SCI patients and five healthy subjects (rectal volume reduction = 38 +/- 4% and 41 +/- 3% in SCI patients and healthy subjects, respectively), with a time effect in the first 30 min (P < 0.0001) but no group effect in the second 30 min. Intact neural transmission between the spinal cord and higher centers is not essential for normal colorectal motor responses to feeding and distension; however, a degree of central nervous system and neurohormonal modulation of these responses is likely.

Basic and clinical aspects of gastrointestinal pain

The gastrointestinal (GI) tract is a system of organs within multicellular animals which facilitates the ingestion, digestion, and absorption of food with subsequent defecation of waste. A complex arrangement of nerves and ancillary cells contributes to the sensorimotor apparatus required to subserve such essential functions that are with the exception of the extreme upper and lower ends of the GI tract normally subconscious. However, it also has the potential to provide conscious awareness of injury. Although this function can be protective, when dysregulated, particularly on a chronic basis, the same system can lead to considerable morbidity. The anatomical and molecular basis of gastrointestinal nociception, conditions associated with chronic unexplained visceral pain, and developments in treatment are presented in this review.

Pharmacology of inflammatory pain: local alteration in receptors and mediators

BACKGROUND

Inflammation is commonly associated with hyperalgesia. Ideally, this change should abate once inflammation is resolved, but this is not necessarily the case because phenotypic changes in the tissue can persist, as appears to be the case in post-infectious irritable bowel syndrome. Basically, all primary afferent neurons supplying the gut can be sensitized in response to pro-inflammatory mediators, and the mechanisms whereby hypersensitivity is initiated and maintained are, thus, of prime therapeutic interest.

EXPERIMENTAL AND CLINICAL FINDINGS

There is a multitude of molecular nocisensors that can be responsible for the hypersensitivity of afferent neurons. These entities include: (i) receptors and sensors at the peripheral terminals of afferent neurons that are relevant to stimulus transduction, (ii) ion channels that govern the excitability and conduction properties of afferent neurons, and (iii) transmitters and transmitter receptors that mediate communication between primary afferents and second-order neurons in the spinal cord and brainstem. Persistent increases in the sensory gain may result from changes in the expression of transmitters, receptors or ion channels; changes in the subunit composition and biophysical properties of receptors and ion channels; or changes in the structure, connectivity and survival of afferent neurons. Particular therapeutic potential is attributed to targets that are selectively expressed by afferent neurons and whose number and function are altered in abdominal hypersensitivity.

CONCLUSION

Emerging targets of therapeutic relevance include distinct members of the transient receptor potential (TRP) channel family (TRPV1, TRPV4, TRPA1), acid-sensing ion channels, protease-activated receptors, corticotropin-releasing factor receptors and sensory neuron-specific sodium channels.

Relationship of cytochrome P450 pharmacogenetics to the effects of yohimbine on gastrointestinal transit and catecholamines in healthy subjects

Alpha-2 adrenergic receptors tonically inhibit colonic motility and the alpha(2)-adrenergic antagonist yohimbine, given intravenously, increased colonic tone in humans. However, the effect of yohimbine on colonic transit in humans is unknown. In this study, 30 healthy volunteers were randomized to yohimbine 16.2 mg p.o. t.i.d. or identical placebo for 7 days. We evaluated gastric emptying, small intestinal, and colonic transit by scinitigraphy, bowel habits, haemodynamics and plasma catecholamines. As cytochrome P450 enzymes metabolize yohimbine, P450 genotypes (CYP2D6 and CYP3A4) were determined in 25 of 30 subjects who consented to genetic studies. The relationship between drug metabolizer status predicted by CYP2D6 and CYP3A4 and effects of yohmibine were assessed. Compared to placebo, yohimbine increased (P < or = 0.02) diastolic blood pressure, plasma noradrenaline concentrations and maximum tolerated volume during the satiation test [yohimbine (1241 +/- 88, mean +/- SEM) vs placebo (1015 +/- 87), P = 0.054]. However, yohimbine did not affect gastrointestinal transit. Based on CYP2D6 and CYP3A4 alleles, seven and 18 subjects were, respectively, extensive (EM) and poor (PM) metabolizers of yohimbine. Compared to EM, PM of yohimbine had a greater increase in plasma noradrenaline (P = 0.1 for PM vs EM), lower maximum tolerated volumes (1120 +/- 95 vs 1484 + 131 mL, P = 0.02), and faster colonic transit (i.e. GC(24) was 3.0 +/- 0.4 vs 2.1 +/- 0.5, P = 0.1). These data suggest that CYP2D6 and CYP3A4 genotypes which determine the metabolism of yohimbine may influence its sympathetic and gastrointestinal effects.

Effects of pregabalin on visceral pain responses and colonic compliance in rats

BACKGROUND AND PURPOSE

Pregabalin, which binds to the alpha2-delta subunit of voltage-gated calcium channels, increased the threshold for pain during colorectal distension (CRD) in irritable bowel syndrome (IBS) patients. We tested the effects of oral pregabalin on the visceral pain-related viscerosomatic and autonomic cardiovascular responses to CRD and colonic compliance in rats.

EXPERIMENTAL APPROACH

The activity of the abdominal musculature (viscerosomatic response), monitored by electromyography and intracolonic manometry, and changes in blood pressure and heart rate, monitored by telemetry, were assessed simultaneously in conscious rats during CRD.

KEY RESULTS

Pregabalin (10-200 micromol kg(-1), p.o.) inhibited dose dependently the viscerosomatic response to phasic, noxious CRD (12 distensions at 80 mm Hg). At 200 mumol kg(-1), pregabalin also reduced the increase in blood pressure and heart rate associated with noxious CRD. Moreover, pregabalin (200 micromol kg(-1), p.o.) reduced the visceromotor response to ascending phasic CRD (10-80 mm Hg) and significantly increased the threshold pressure for response. During phasic CRD (2-20 mm Hg), pregabalin (200 micromol kg(-1), p.o.) increased intracolonic volume, resulting in a shift to the left of the pressure-volume relationship curve, indicative of an increase of compliance.

CONCLUSIONS AND IMPLICATIONS

Pregabalin reduced the viscerosomatic and autonomic responses associated with CRD-induced visceral pain and increased colonic compliance in rats. These observations confirm the analgesic activity of pregabalin on visceral pain and support the translational value of the CRD model to humans. Ligands for the alpha2-delta subunit might represent interesting compounds for the treatment of visceral pain disorders, such as IBS.

Oral clonidine inhibits visceral pain-related viscerosomatic and cardiovascular responses to colorectal distension in rats

The alpha(2)-adrenoceptor agonist, clonidine, modulates colorectal sensorimotor functions in humans and, given intrathecally, has analgesic effects in the colorectal distension (CRD) model in rats. We tested the effects of systemic clonidine on the visceral pain-related viscerosomatic and autonomic cardiovascular responses to CRD and colonic compliance in rats using clinically relevant CRD protocols. The activity of the abdominal musculature (viscerosomatic response), monitored by electromyography and intracolonic manometry, and changes in arterial blood pressure and heart rate, monitored by telemetry, were assessed simultaneously in conscious rats during CRD. Pressure-volume relationships during CRD served as a measure of colonic compliance. Clonidine (50-200 nmol/kg, p.o.) dose-dependently inhibited the viscerosomatic response to phasic, noxious CRD (12 distension at 80 mm Hg). At 200 nmol/kg clonidine also attenuated the increase in blood pressure (70+/-7% inhibition, P<0.05) and heart rate (67+/-16% inhibition, P<0.05) associated to noxious CRD. Similar effects were observed after i.v. administration. Likewise, clonidine (200 nmol/kg, p.o.) reduced the response to ascending phasic CRD (10-80 mm Hg) and significantly increased the threshold pressure for pain-related responses. Clonidine (50 or 150 nmol/kg, i.p.) did not affect the pressure-volume relationship during phasic CRD (2-20 mm Hg). These results show that systemic clonidine, at doses devoid of visible side effects, has analgesic effects in the CRD model of visceral pain in rats without affecting colonic compliance. These observations confirm the analgesic activity of systemic clonidine on visceral pain, support the translational value of the rat CRD model to humans and show that manometry is more sensitive than electromyography detecting pain-related responses.

Updates on treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by abdominal pain and discomfort in association with altered bowel habits. It is estimated to affect 10%-15% of the Western population, and has a large impact on quality of life and (in)direct healthcare costs. IBS is a multifactorial disorder involving dysregulation within the brain-gut axis, and it is frequently associated with gastrointestinal motor and sensory dysfunction, enteric and central nervous system irregularities, neuroimmune dysregulation, and post-infectious inflammation. As with other functional medical disorders, the treatment for IBS can be challenging. Conventional therapy for those with moderate to severe symptoms is largely unsatisfactory, and the development of new and effective drugs is made difficult by the complex pathogenesis, variety of symptoms, and lack of objective clinical findings that are the hallmark of this disorder. Fortunately, research advances over the past several decades have provided insight into potential mechanisms responsible for the pathogenesis of IBS, and have led to the development of several promising pharmaceutical agents. In recent years there has been much publicity over several of these new IBS medications (alosetron and tegaserod) because of their reported association with ischemic colitis and cardiovascular disease. While these agents remain available for use under restricted prescribing programs, this highlights the need for continued development of safe and effective medication for IBS. This article provides a physiologically-based overview of recently developed and frequently employed pharmaceutical agents used to treat IBS, and discusses some non-pharmaceutical options that may be beneficial in this disorder.

Characterisation of colonic accommodation in Wistar Kyoto rats with impaired gastric accommodation

Defective colonic and gastric accommodations have been related to altered viscerosensitivity in irritable bowel syndrome and to functional dyspepsia, respectively. We assessed colonic accommodation in rats with impaired gastric accommodation to determine if altered accommodation can be regarded as a widespread pathophysiological alteration within the gastrointestinal (GI) tract. Colonic accommodation during colorectal distension (CRD) was assessed in Wistar Kyoto rats (WKY), an animal model of impaired gastric accommodation, and in Sprague-Dawley (SD) and Wistar rats, considered normal. CRD (10-80 mmHg)-induced visceral pain responses were also evaluated in the same strains of rats. During gastric distension, WKY rats had lower intra-gastric volume (0.96 +/- 0.22 ml) than SD (1.85 +/- 0.19 ml, P < 0.05) or Wistar rats (2.80 +/- 0.26 ml, P < 0.05), indicating impaired gastric accommodation. In the same animals, pressure-volume curves were constructed during CRD as a measure of colonic accommodation. During short-lasting (1 min) phasic CRD (2-20 mmHg), the pressure-volume curve in WKY rats was displaced to the right compared with SD or Wistar rats, indicative of reduced colonic accommodation (maximal volume: SD, 1.22 +/- 0.05 ml; Wistar, 1.07 +/- 0.04 ml; WKY, 0.87 +/- 0.07 ml; P < 0.01). Pre-treatment with atropine normalised the pressure-volume responses in WKY rats. No differences among strains were observed during the 2-min phasic or ramp-tonic CRD. Visceral pain responses during CRD (10-80 mmHg) were, overall, similar in the three strains, although WKY rats showed lower thresholds for pain (28.0 +/- 4.9 mmHg) than SD (42.3 +/- 6.6 mmHg, P = 0.072) or Wistar rats (48.3 +/- 6.0 mmHg, P < 0.05). WKY rats, although having impaired gastric accommodation, have the ability to fully accommodate the colon to increasing pressures. In WKY rats, impaired accommodation of the smooth muscle might not be a widespread phenomenon along the GI tract but rather a local disturbance.

The serotonin reuptake inhibitor citalopram does not affect colonic sensitivity or compliance in rats

Altered serotonin signaling has been implicated in the pathophysiology of irritable bowel syndrome (IBS). Selective serotonin reuptake inhibitors (SSRI) improve IBS symptoms, although the mechanism of action remains unclear. We assessed the effects of the SSRI, citalopram, on colonic sensitivity and compliance in rats after acute and repeated administration. Colorectal distension was performed in conscious rats. Pressure-volume relationships during colorectal distension (2-20 mmHg), fitted using a power exponential model [Vol=V(max)xexp[-(kappaxRelP)(beta)], were used as a measure of colonic compliance. The visceral pain-related visceromotor response during colorectal distension (10-80 mmHg) was used to assess visceral sensitivity. Pressure-volume curves and visceromotor responses were assessed after acute citalopram (3 or 10 mg/kg, ip) or vehicle and after repeated treatment (7 and 14 days; 3 or 10 mg/kg/day). In vehicle-treated animals, pressure-volume curves were similar over time. Citalopram (acute or repeated treatment) did not affect neither the pressure-volume curves nor the visceromotor response to colorectal distension. Thus, citalopram, after acute or repeated administration, had no significant effects on colon compliance or visceral pain during colorectal distension in rats. These results agree with recent observations in humans suggesting that the therapeutic actions of citalopram in IBS are independent of any effects on colonic sensorimotor function.

Effects of glucagon-like peptide-1 and sympathetic stimulation on gastric accommodation in humans

In humans, glucagon-like peptide-1 (GLP-1) delays gastric emptying by inhibiting vagal activity and also increases gastric volumes, by unclear mechanisms. Because GLP-1 inhibits intestinal motility by stimulating the sympathetic nervous system in rats, we assessed the effects of a GLP-1 agonist and yohimbine, an alpha(2)-adrenergic antagonist, on gastric volumes in humans. In this double-blind study, 32 healthy volunteers were randomized to placebo, a GLP-1 agonist, yohimbine or GLP-1 and yohimbine. Gastric volumes (fasting predrug and postdrug, and postprandial postdrug) were measured by (99m)Tc single photon emission computed tomography imaging. Plasma catecholamines and haemodynamic parameters were assessed. Compared with placebo, GLP-1 increased (P = 0.03) but yohimbine did not affect fasting gastric volume. However, GLP-1 plus yohimbine increased (P < 0.001) postprandial gastric accommodation vs placebo and vs GLP-1 alone [postprandial volume change = 542 +/- 29 mL (mean +/- SEM, placebo), 605 +/- 31 mL (GLP-1), 652 +/- 54 mL (yohimbine) and 810 +/- 37 mL (GLP-1 and yohimbine)]. Plasma noradrenaline and dihydroxyphenylglycol concentrations were higher for yohimbine vs placebo and for GLP-1 and yohimbine vs GLP-1. Yohimbine stimulates central sympathetic activity and in combination with GLP-1, augments postprandial accommodation in humans.

Feeding and colonic distension provoke altered autonomic responses in irritable bowel syndrome

OBJECTIVE

Alterations in autonomic balance, detectable by heart rate variability (HRV) analysis, have been shown to occur after a meal in patients with irritable bowel syndrome (IBS). There are few data on changes in sympathovagal responses in IBS to other forms of enteric stimulation such as colonic distension. The aim of this study was to determine the effects of colonic balloon distension on HRV in the fasting and the postprandial state in healthy subjects and in IBS patients.

MATERIAL AND METHODS

Eight IBS patients and 8 age- and gender-matched healthy subjects underwent unsedated descending colonic distension before and after a 1000 kcal liquid meal. Low- (LF) and high-frequency (HF) HRV band values obtained from 2-min ECG segments recorded before and during distension were compared between groups, and between fasting and postprandial states. A visual analogue scale was used to determine sensation during colonic distension.

RESULTS

HF values decreased significantly with feeding in IBS patients (p=0.01), but not in healthy subjects. The low-to-high frequency (LF/HF) ratio was significantly higher postprandially in IBS patients (p=0.02) and, additionally, was decreased (p<0.01) with colonic distension in the fed state, independently of colonic sensitivity or distending volume. Moreover, changes in the LF/HF ratio with distension in the fed versus the fasting state were negatively correlated in IBS patients but positively correlated in healthy subjects (both p<0.05).

CONCLUSIONS

IBS patients demonstrated altered autonomic responses to feeding and colonic distension. Further studies should determine whether these alterations could explain the postprandial exacerbation of symptoms in IBS.

Irritable bowel syndrome: recent and novel therapeutic approaches

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal disorder affecting up to 3-15% of the general population in Western countries. It is characterised by unexplained abdominal pain, discomfort and bloating in association with altered bowel habits. The pathophysiology of IBS is considered to be multifactorial, involving disturbances of the brain-gut-axis: IBS has been associated with abnormal gastrointestinal motor functions, visceral hypersensitivity, psychosocial factors, autonomic dysfunction and mucosal inflammation. Traditional IBS therapy is mainly symptom oriented and often unsatisfactory. Hence, there is a need for new treatment strategies. Increasing knowledge of brain-gut physiology, mechanisms, and neurotransmitters and receptors involved in gastrointestinal motor and sensory function have led to the development of several new therapeutic approaches. This article provides a systematic overview of recently approved or novel medications that show promise for the treatment of IBS; classification is based on the physiological systems targeted by the medication. The article includes agents acting on the serotonin receptor or serotonin transporter system, novel selective anticholinergics, alpha-adrenergic agonists, opioid agents, cholecystokinin antagonists, neurokinin antagonists, somatostatin receptor agonists, neurotrophin-3, corticotropin releasing factor antagonists, chloride channel activators, guanylate cyclase-c agonists, melatonin and atypical benzodiazepines. Finally, the role of probiotics and antibacterials in the treatment of IBS is summarised.

Current gut-directed therapies for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that can present with a wide array of symptoms that make treatment difficult. Current therapies are directed at relieving symptoms of abdominal pain or discomfort, bloating, constipation, and diarrhea. Pharmacologic agents used to treat IBS-associated pain include myorelaxants, peppermint oil, and peripherally acting opiates. Dicyclomine and hyoscyamine, the two myorelaxants available in the United States, have not been proven effective in reducing abdominal pain in patients with IBS. The efficacy of peppermint oil is debated, but methodological problems with existing studies preclude definitive judgment. Loperamide is ineffective for relief of abdominal pain. For IBS patients with excessive abdominal bloating, a small number of studies suggest that bacterial eradication with gut-directed antibiotics and bacterial reconstitution with nonpathogenic probiotics may reduce flatulence. For constipation-predominant (C-IBS) symptoms, current treatment options include fiber supplementation, polyethylene glycol, and tegaserod. Soluble fibers (ispaghula, calcium polycarbophil, psyllium) are more effective than insoluble fibers (wheat bran, corn fiber) in alleviating global symptoms and relieving constipation, although fiber in general has marginal benefit in treatment of overall IBS symptoms. Polyethylene glycol increases bowel frequency in chronic constipation, but its overall efficacy against IBS is unclear. Tegaserod, a 5-HT(4) agonist, demonstrates superiority over placebo in improving bowel frequency and stool consistency and alleviating abdominal pain and bloating in women with C-IBS. Overall global symptoms are modestly improved with tegaserod when compared with placebo. Additional agents under investigation for C-IBS include the ClC(2) chloride channel opener lubiprostone, mu-opioid receptor antagonist alvimopan, and 5-HT(4) agonist renzapride. For diarrhea-predominant (D-IBS) symptoms, available therapies include loperamide, alosetron, and clonidine. Alosetron, a 5-HT(3) antagonist, is superior to placebo for reducing bowel frequency, improving stool consistency, and relieving abdominal pain in women with D-IBS. However, alosetron is available under a restricted license because of concerns for ischemic colitis and severe constipation necessitating colectomy. Clonidine may be helpful in alleviating global symptoms for D-IBS patients.

Treatment of gastroparesis: a multidisciplinary clinical review

This clinical review on the treatment of patients with gastroparesis is a consensus document developed by the American Motility Society Task Force on Gastroparesis. It is a multidisciplinary effort with input from gastroenterologists and other specialists who are involved in the care of patients with gastroparesis. To provide practical guidelines for treatment, this document covers results of published research studies in the literature and areas developed by consensus agreement where clinical research trials remain lacking in the field of gastroparesis.

Pharmacological and pharmacokinetic aspects of functional gastrointestinal disorders

Medications are commonly used for the treatment of patients with functional gastrointestinal disorders. The general goal of this report is to review the pharmacokinetics and pharmacology of medications used in functional gastrointestinal disorders. Methods included literature review, consensus evaluation of the evidence for each topic assigned originally to 1 or 2 authors, and broader review at a harmonization session as part of the Rome III process. This report reviews the animal models that have been validated for the study of effects of pharmacologic agents on sensation and motility; the preclinical pharmacology, pharmacokinetics, and toxicology usually required for introduction of novel therapeutic agents; the biomarkers validated for studies of sensation and motility end points with experimental medications in humans; the pharmacogenomics applied to these medications and disorders; and the pharmacology of agents that are applied or have potential for treatment of functional gastrointestinal disorders, including psychopharmacologic agents. Clinician and basic investigators involved in the treatment or investigation of functional gastrointestinal disorders or disease models need to have a comprehensive understanding of a vast range of medications. It is anticipated that the interaction between investigators of basic science, basic and applied pharmacology, and clinical trials will lead to better treatment of these disorders.

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.

The anxiogenic drug yohimbine activates central viscerosensory circuits in rats

Systemic administration of the alpha(2)-adrenoceptor antagonist yohimbine (YO) activates the HPA stress axis and promotes anxiety in humans and experimental animals. We propose that visceral malaise contributes to the stressful and anxiogenic effects of systemic YO and that YO recruits brainstem noradrenergic (NA) and peptidergic neurons that relay viscerosensory signals to the hypothalamus and limbic forebrain. To begin testing these hypotheses, the present study explored dose-related effects of YO on food intake, conditioned flavor avoidance (CFA), and Fos immunolabeling in rats. Systemic YO (5.0 mg/kg BW, i.p.) inhibited food intake, supported CFA, and increased Fos immunolabeling in identified NA neurons in the ventrolateral medulla, nucleus of the solitary tract, and locus coeruleus. YO also increased Fos in the majority of corticotropin releasing hormone-positive neurons in the paraventricular nucleus of the hypothalamus. YO administered at 1.0 mg/kg BW did not inhibit food intake, did not support CFA, and did not increase Fos immunolabeling. Retrograde neural tracing demonstrated that neurons activated by YO at 5.0 mg/kg BW included medullary and pontine neurons that project to the central nucleus of the amygdala and to the lateral bed nucleus of the stria terminalis, the latter region receiving comparatively greater input by Fos-positive neurons. We conclude that YO produces anorexigenic and aversive effects that correlate with activation of brainstem viscerosensory inputs to the limbic forebrain. These findings invite continued investigation of how central viscerosensory signaling pathways interact with hypothalamic and limbic regions to influence interrelated physiological and behavioral components of anxiety, stress, and visceral malaise.

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.

Increased beta-adrenergic sensitivity correlates with visceral hypersensitivity in patients with constipation-predominant irritable bowel syndrome

Autonomic imbalance has been proposed to be a pathophysiological factor for irritable bowel syndrome (IBS). The aim of this study was to assess beta-adrenergic abnormalities in IBS and to evaluate their relationship to visceral hypersensitivity and other symptoms of IBS patients. Sixteen IBS patients and 16 control subjects were recruited into this study. Participants were asked to complete a questionnaire regarding bowel symptoms, and in order to study beta-adrenergic sensitivity, isoproterenol stimulation tests were performed and visceral hypersensitivity was evaluated by barostat test. Results showed that beta-adrenergic activity and rectal sensitivity were more pronounced in IBS patients than in normal control patients (P < 0.01). Although both IBS subgroups also exhibited more pronounced beta-adrenergic sensitivity than did the controls (P < 0.05), a significant correlation between beta-adrenergic activity and maximally tolerable pressures on the barostat test was found only in IBS-C patients (P = 0.03, R = 0.855). In addition, patients with "hard or lumpy" stools exhibited a higher degree of beta-adrenergic activity (P = 0.00). We conclude that increased beta-adrenergic activity significantly correlated with visceral hypersensitivity in constipation-predominant IBS and symptoms of hard or lumpy stools in IBS patients.

New and emerging treatments for irritable bowel syndrome and functional dyspepsia

The symptomatic management of irritable bowel syndrome (IBS) and functional dyspepsia, which often overlap, can be frustrating and difficult. Education and reassurance remain central for management although controlled trials are lacking. Psychological interventions may be useful in select patients but methodological inadequacies in clinical trials limit their interpretability. For symptom exacerbations, drug treatment is reasonable but no current treatment successfully targets the full symptom complex. Bulking agents are not of proven efficacy in IBS; they may improve constipation but worsen bloating and pain. Anticholinergics are of uncertain value in IBS. A meta-analysis of trials of smooth muscle relaxants for IBS has been reported to be positive but the quality of the trials included was poor. Antidepressants for IBS and functional dyspepsia appear to be efficacious based on the limited published evidence; both global symptoms and abdominal pain improve. Selective serotonin reuptake inhibitors (SSRIs) are of uncertain efficacy but anecdotally appear to be useful. Laxatives are not of proven efficacy in IBS. Loperamide improves diarrhea, but not abdominal pain in IBS. No drug is of proven efficacy for bloating. Acid suppression remains the mainstay of therapy for functional dyspepsia but the majority of patients do not have an adequate response. Promising drugs include new prokinetics for constipation-predominant IBS (e.g., tegaserod, a partial 5-HT4 agonist, prucalopride, a full 5-HT4 agonist, and dexloxiglumide, a cholecystokinin1 antagonist), agents for diarrhea-predominant IBS (e.g., 5-HT3 antagonists, alpha2 receptor agonists and corticotrophin receptor-1 antagonists), other visceral analgesics (e.g. tachykinin antagonists, opioid agonists) and in dyspepsia fundus relaxing agents (e.g., 5-HT1 agonists, tegaserod).

Meta-analysis: The treatment of irritable bowel syndrome

To evaluate therapies available for the treatment of irritable bowel syndrome, and provide consensus recommendations for their use, a total of 51 double-blind clinical trials using bulking agents, prokinetics, antispasmodics, alosetron, tegaserod and antidepressants were selected. The quality of studies was assessed using 5-point scale. Meta-analyses were performed on all studies, and on 'high-quality studies'. The efficacy of fibre in the global irritable bowel syndrome symptoms relief (OR: 1.9; 95% CI:1.5-2.4) was lost after exclusion of low-quality trials (OR: 1.4; 95% CI: 1.0-2.0, P = 0.06). When excluding the low-quality trials, an improvement of global irritable bowel syndrome symptoms with all antispasmodics (OR: 2.1; 95% CI:1.8-2.9) was maintained only for octylonium bromide, but on the basis of only two studies. Antidepressants were effective (OR: 2.6, 95% CI: 1.9-3.5), even after exclusion of low-quality studies (OR: 1.9, 95% CI: 1.3-2.7). Alosetron (OR: 2.2; 95% CI: 1.9-2.6) and tegaserod (OR: 1.4; 95% CI: 1.2-1.5) showed a significant effect in women. We recommend the use of tegaserod for women with irritable bowel syndrome with constipation and alosetron for women with severe irritable bowel syndrome with diarrhoea. Antidepressants can be beneficial for irritable bowel syndrome with diarrhoea patients with severe symptoms. Loperamide can be recommended in painless diarrhoea. Evidence is weak to recommend the use of bulking agents in the treatment of irritable bowel syndrome with constipation.

Modulatory influences on antegrade and retrograde tonic reflexes in the colon and rectum

Tonic reflexes in the colon and rectum are likely to be important in health and in disorders of gastrointestinal function. The aim of this study was to evaluate the fasting and postprandial "colorectal" and "rectocolic" reflexes in response to 2-min isobaric distensions of the colon and rectum, accounting for enteric sensation, compliance, and distending balloon volume. In 14 healthy fasting subjects, a dual barostat assembly was positioned (descending colon and rectum). A 2-min phasic distension was performed in the colon and rectum in random order while the opposing balloon volume was recorded. Sensation (phasic distension) and compliance (ramp distension) were also determined. The experiment was repeated postprandially. Colonic distension resulted in significant rectal tonic contraction in the fasting (rectal volume change: -35.4 +/- 8.4 ml, P < 0.01) and postprandial (-22.2 +/- 8.4 ml, P < 0.01) states. After adjustment for colonic sensitivity, for compliance, and for distending balloon volume, the rectal volume change remained significant; the extent of the tonic response, however, correlated significantly with increasing pain score (P < 0.01). In contrast, rectal distension did not produce a significant tonic response in the colon (fasting: -6.5 +/- 7.3 ml; postprandial: 2.7 +/- 7.3 ml), either unadjusted or adjusted for rectal sensitivity, compliance, and distending balloon volume. In conclusion, the colorectal reflex, but not the rectocolic reflex, can be readily demonstrated both before and after a meal in response to a 2-min isobaric distension in the colon and rectum, respectively. Although the presence of the colorectal reflex does not depend on colonic sensitivity or the volume of the distending colonic balloon, these factors modulate the reflex, especially in the fasting state.

Interactions between the cardiovascular and pain regulatory systems: an updated review of mechanisms and possible alterations in chronic pain

Endogenous pain regulatory system dysfunction appears to play a role in the maintenance of chronic pain. An important component of the pain regulatory process is the functional interaction between the cardiovascular and pain regulatory systems, which results in an association between elevated resting blood pressure (BP) and diminished acute pain sensitivity. This BP/pain sensitivity relationship is proposed to reflect a homeostatic feedback loop helping restore arousal levels in the presence of painful stimuli. Evidence is emerging that this normally adaptive BP/pain sensitivity relationship is significantly altered in chronic pain conditions, affecting responsiveness to both acute and chronic pain stimuli. Several mechanisms that may underlie this adaptive relationship in healthy individuals are overviewed, including endogenous opioid, noradrenergic, and baroreceptor-related mechanisms. Theoretical models are presented regarding how chronic pain-related alterations in the mechanisms above and increased pain facilatory system activity (central sensitization) may contribute to altered BP/pain sensitivity interactions in chronic pain. Clinical implications are discussed.

Treating irritable bowel syndrome: overview, perspective and future therapies

This article summarizes the ongoing challenges in irritable bowel syndrome and the exciting opportunities for development of novel therapies for this common, enigmatic condition. The challenges include insufficient understanding of mechanisms, lack of specificity of symptoms, differentiation from other conditions, and lack of availability of noninvasive tests to identify dysfunctions. However, significant opportunities are reflected by the advances in clinical trial design and, particularly, clinically relevant end points for such trials, and the increasing understanding of basic neuroenteric science. The latter has delivered two new medications to the practice (alosetron and tegaserod), and other candidate therapies (other serotonergic, tachykininergic, opioid, cannabinoid modulators) are being carefully appraised as potential drugs for the future.

Altered prejunctional modulation of intestinal cholinergic and noradrenergic pathways by alpha2-adrenoceptors in the presence of experimental colitis

1 This study investigates the influence of intestinal inflammation on: (1) the control of intestinal neurotransmission and motility by prejunctional alpha(2)-adrenoceptors and (2) the expression of intestinal alpha(2)-adrenoceptors. Experimental colitis was induced by intrarectal administration of 2,4-dinitrobenzenesulphonic acid (DNBS) to rats. 2 UK-14,304 inhibited atropine-sensitive electrically evoked contractions of ileal and colonic longitudinal muscle preparations. UK-14,304 acted with similar potency, but higher efficacy, on tissues from DNBS-treated animals; its effects were antagonized with greater potency by phentolamine than rauwolscine. 3 Electrically induced [(3)H]noradrenaline release from ileal preparations was reduced in the presence of colitis. Tritium outflow was decreased by UK-14,304 and stimulated by rauwolscine or phentolamine: these effects were enhanced in preparations from animals with colitis. 4 Reverse transcription-polymerase chain reaction and Western blot assay demonstrated the protein expression of alpha(2A)-adrenoceptors in mucosal and muscular tissues isolated from ileum and colon. The induction of colitis increased alpha(2A)-adrenoceptor expression in both ileal and colonic muscular layers, without concomitant changes in mucosal tissues. 5 Induction of colitis reduced gastrointestinal propulsion of a charcoal suspension in vivo. In this setting, the gastrointestinal transit was inhibited by intraperitoneal (i.p.) UK-14,304 and stimulated by i.p. rauwolscine. After pretreatment with guanethidine, the stimulant action of rauwolscine no longer occurred, and UK-14,304 exerted a more prominent inhibitory effect that was antagonized by rauwolscine. 6 The present results indicate that, in the presence of intestinal inflammation, prejunctional alpha(2)-adrenoceptors contribute to an enhanced inhibitory control of cholinergic and noradrenergic transmission both at inflamed and noninflamed distant sites. Evidence was obtained that such modulatory actions depend on an increased expression of alpha(2A)-adrenoceptors within the enteric nervous system.

Novel therapies in the treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterised by abnormalities in motility, sensation and perception. It is one of the most common conditions encountered in clinical practice, especially by gastroenterologists. Pharmacological treatment of IBS is aimed at the predominant symptom and recent advances in pathophysiology has opened the door to the development of new compounds that target specific receptors. During this review, the most promising investigational and recently approved drugs will be discussed.

Pharmacologic therapy for the irritable bowel syndrome

The management of the irritable bowel syndrome (IBS) remains unsatisfactory. For abdominal pain, antispasmodics are, at best, of only modest efficacy. Tricyclic antidepressants in low dose are useful (with the number needed to treat being three), but side effects and patient concerns regarding use of a centrally acting agent for depression remain limitations. Selective serotonin reuptake inhibitors are of uncertain efficacy in IBS. Opioid agonists, especially loperamide, are useful for diarrhea but not for pain in IBS; rebound constipation also remains a problem. Bile salt sequestering agents are not of established value in IBS but seem to be useful clinically in a small group of IBS patients with diarrhea. Aloestron, a 5HT(3) antagonist, should be reserved, if available, for women with severe diarrhea predominant IBS who have failed to respond to conventional therapy, and started at a low dose. Fiber and bulking agents may help constipation in some trials, but the evidence that they are efficacious in IBS is equivocal; they are frequently prescribed as first-line drugs for IBS regardless of the primary bowel disturbance but often increase bloating, gas, and pain. Laxatives are not of established value in IBS but are often taken by patients with constipation predominant IBS. Tegaserod, a partial 5HT(4) agonist, is now available in the United States and other countries for use in women with IBS whose primary bowel symptom is constipation; its efficacy in men and in those with alternating bowel habits is unknown. Probiotics are of uncertain efficacy. Chinese herbal medicine data are insufficient. Other new drugs in development include the cholecystokinin antagonists and novel visceral analgesics. Both current and potential therapies for IBS are reviewed in this article.

A randomized, controlled exploratory study of clonidine in diarrhea-predominant irritable bowel syndrome

BACKGROUND & AIMS

The aim of this study was to evaluate the efficacy and tolerability of the alpha-2 adrenoreceptor agonist, clonidine, in patients with diarrhea-predominant irritable bowel syndrome (D-IBS) in a double-blind, randomized, parallel-group, placebo-controlled trial.

METHODS

A 2-week run-in evaluated baseline symptoms. Patients received 0.05, 0.1, or 0.2 mg clonidine or placebo twice a day for 4 weeks. We evaluated satisfactory relief of IBS by weekly question and stool parameters with a daily diary. Satisfactory relief and overall bowel function were primary end points. Secondary end points were stool frequency, consistency, and ease of passage; gut transit; and fasting and postprandial gastric volumes. Analysis followed intention-to-treat principles.

RESULTS

Forty-four D-IBS patients participated; there were 4 treatment-related dropouts: 2/2 in the 0.2-mg and 2/12 in the 0.05-mg clonidine groups. Proportion with satisfactory relief of IBS was 0.46, 0.42, and 0.67 with placebo, 0.05 mg, and 0.1 mg clonidine, respectively. Relief was sustained through 4 weeks of treatment, and bowel dysfunction (firmer stools and easier stool passage [P < 0.05]) was reduced with clonidine, 0.1 mg twice a day. Clonidine did not significantly alter gastrointestinal transit or gastric volumes. Drowsiness, dizziness, and dry mouth were the most common adverse events with the 0.1-mg dose; severity of adverse effects subsided after the first week of treatment. A trial to replicate 20% or more responders with clonidine will require 95 patients per treatment arm.

CONCLUSIONS

Clonidine, 0.1 mg twice a day for 4 weeks, relieves bowel dysfunction and appears promising for relief of D-IBS; these effects are unassociated with significant alterations in transit.