The effect of octreotide on human gastric compliance and sensory perception

The role of experimental models in developing new treatments for irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized by chronic, recurrent abdominal pain and altered bowel habits and is currently defined by symptom criteria and the absence of detectable organic disease. The underlying pathophysiology remains incompletely understood. Despite considerable efforts by the scientific community and the pharmaceutical industry to develop novel pharmacological treatments aimed at chronic visceral pain, the traditional approach to identifying and evaluating novel drugs for this target have largely failed to translate into effective IBS treatments. However, several novel drugs aimed at normalizing bowel movements have produced clinical effects, not only on the primary target, but also on pain and discomfort. While some of the commonly used experimental animal models for the pain dimension of IBS have some face and construct validity, the predictive validity of most of the models is either unknown, or has been disappointing. A reverse translational approach is proposed, which is based on identification and characterization of brain endophenotypes in patients, followed by translation of these endophenotypes for pharmacological studies in rodent models.

Reduced brainstem inhibition during anticipated pelvic visceral pain correlates with enhanced brain response to the visceral stimulus in women with irritable bowel syndrome

Cognitive factors such as fear of pain and symptom-related anxiety play an important role in chronic pain states. The current study sought to characterize abnormalities in preparatory brain response before aversive pelvic visceral distention in irritable bowel syndrome (IBS) patients and their possible relationship to the consequences of distention. The brain functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) response to anticipated and delivered mild and moderate rectal distention was recorded from 14 female IBS patients and 12 healthy controls. During cued anticipation of distention, activity decreased in the insula, supragenual anterior cingulate cortex (sACC), amygdala, and dorsal brainstem (DBS) of controls. IBS patients showed less anticipatory inactivation. Group differences were significant in the right posterior insula and bilateral DBS. Self-rated measures of negative affect during scanning were higher in patients than controls (p < 0.001), and the anticipatory BOLD decreases in DBS were inversely correlated with these ratings. During subsequent distention, both groups showed activity increases in insula, dorsal ACC, and DBS and decreases in the infragenual ACC. The increases were more extensive in patients, producing significant group differences in dorsal ACC and DBS. The amplitude of the anticipatory decrease in the pontine portion of DBS was associated with greater activation during distention in right orbitofrontal cortex and bilateral sACC. Both regions have been associated previously with corticolimbic inhibition and cognitive coping. Deficits in preparatory inhibition of DBS, including the locus ceruleus complex and parabrachial nuclei, may interfere with descending corticolimbic inhibition and contribute to enhanced brain responsiveness and perceptual sensitivity to visceral stimuli in IBS.

Effect of long-term treatment with octreotide on rectal sensitivity in patients with non-constipated irritable bowel syndrome

BACKGROUND

Acute administration of octreotide reduces visceral perception and therefore has been suggested as potential treatment for irritable bowel syndrome. Whether prolonged treatment with octreotide also reduces visceral sensitivity and improves gastrointestinal symptoms remains, however, unknown.

AIM

To investigate the effect of a slow release preparation of octreotide on rectal sensitivity and symptoms in irritable bowel syndrome patients.

METHODS

Forty-six non-constipated irritable bowel syndrome patients (52% female, 19-63 years) participated. Before and after 8 weeks of treatment with octreotide (Sandostatin LAR 20 mg i.m.) or placebo, patients underwent a barostat study to assess the rectal sensitivity. During a 2-week run-in period and treatment, abdominal pain, defecation frequency, consistency and symptom relief were scored weekly.

RESULTS

Octreotide, but not placebo, significantly increased the threshold for first sensation. Thresholds for urge to defecate and discomfort/pain and rectal compliance were not altered by either treatment. Octreotide improved stool consistency compared with placebo (loose stools after eight weeks: octreotide: 52%, placebo: 81%, P < 0.05). In contrast, abdominal pain and defecation frequency were not affected.

CONCLUSIONS

Although the threshold of first rectal sensation increased and stool consistency improved, long-term treatment with octreotide, at least at the current dose used, has no visceral analgesic effect and fails to improve irritable bowel syndrome symptoms.

Review article: modulation of the brain-gut axis as a therapeutic approach in gastrointestinal disease

BACKGROUND

The importance of bi-directional brain-gut interactions in gastrointestinal illness is increasingly being recognized, most prominently in the area of functional gastrointestinal disorders. Numerous current and emerging therapies aimed at normalizing brain-gut interactions are a focus of interest, particularly for irritable bowel syndrome and functional dyspepsia.

METHODS

A literature search was completed for preclinical and clinical studies related to central modulation of gastrointestinal functions and published in English between 1980 and 2006.

RESULTS

Existing data, while sparse, support the use of different classes of antidepressant drugs, including tricyclics, and selective and non-selective serotonin reuptake inhibitors in irritable bowel syndrome. Serotonin receptor agonists and antagonists with peripheral and possibly central effects are effective in treating specific subtypes of irritable bowel syndrome. Based largely on theoretical and preclinical evidence, several novel compounds that selectively target receptors at multiple levels within the brain-gut axis such as neurokinin, somatostatin and corticotropin-releasing factor receptor antagonists are promising.

CONCLUSIONS

This review discusses the rationale for modulation of the brain-gut axis in the treatment of functional gastrointestinal disorders and highlights the most promising current and future therapeutic strategies.

Review article: current and emerging therapies for functional dyspepsia

Functional dyspepsia represents a heterogeneous group of gastrointestinal disorders marked by the presence of upper abdominal pain or discomfort. Although its precise definition has evolved over the last several decades, this disorder remains shrouded in controversy. The symptoms of functional dyspepsia may overlap with those of other functional bowel disorders including irritable bowel syndrome and non-erosive reflux disease. There may be coexistent psychological distress or disease complicating its presentation and response to therapy. Given the prevalence and chronicity of functional dyspepsia, it remains a great burden to society. Suspected physiological mechanisms underlying functional dyspepsia include altered motility, altered visceral sensation, inflammation, nervous system dysregulation and psychological distress. Yet the exact pathophysiological mechanisms that cause symptoms in an individual patient remain difficult to delineate. Numerous treatment modalities have been employed including dietary modifications, pharmacological agents directed at various targets within the gastrointestinal tract and central nervous system, psychological therapies and more recently, complementary and alternative treatments. Unfortunately, to date, all of these therapies have yielded only marginal results. A variety of emerging therapies are being developed for functional dyspepsia. Most of these therapies are intended to normalize pain perception and gastrointestinal motor and reflex function in this group of patients.

Longitudinal change in perceptual and brain activation response to visceral stimuli in irritable bowel syndrome patients

BACKGROUND & AIMS

Symptom-related fears and associated hypervigilance toward visceral stimuli may play a role in central pain amplification and irritable bowel syndrome (IBS) pathophysiology. Repeated stimulus exposure leads to decreased salience of threat and reduction of hypervigilance. We sought to evaluate hypervigilance in IBS visceral hypersensitivity and associated brain activity.

METHODS

Twenty IBS patients (14 female; moderate to severe symptoms) and 14 healthy controls participated in symptom and rectal distention assessments 6 times over 12 months. In a subset of 12 IBS patients, H2 15O-positron emission tomography images were obtained during baseline, rectal distentions, and anticipation of an aversive distention during the first and last session. Statistical parametric mapping (SPM99) was used to identify areas and networks activated during each session as well as those with differential activation across the 2 sessions.

RESULTS

Perceptual ratings of the rectal inflations normalized over 12 months, whereas IBS symptom severity did not. There were no sex-related differences in these response patterns. Stable activation of the central pain matrix was observed over 12 months, and activity in limbic, paralimbic, and pontine regions decreased. During the anticipation condition, there were significant decreases in amygdala, dorsal anterior cingulate cortex, and dorsal brainstem activation at 12 months. Covariance analysis supported the hypothesis of changes in an arousal network including limbic, pontine, and cortical areas underlying the decreased perception seen over the multiple stimulations.

CONCLUSIONS

In IBS patients, repeated exposure to experimental aversive visceral stimuli results in the habituation of visceral perception and central arousal, despite stable activation of networks processing visceral pain and its anticipation.

Concomitant variations of gastric tone and duodenal motility in humans: results of a placebo-controlled study assessing octreotide and sumatriptan

OBJECTIVE

To describe the concomitant effects of octreotide and sumatriptan on fundic tone and duodenal phase III activity.

MATERIAL AND METHODS

A double-blind study was performed in nine volunteers, studied for 2 h after receiving 50 microg octreotide, 6 mg sumatriptan or placebo. Fundic tone variations were assessed by barostat while antroduodenal motility was studied concomitantly using manometry.

RESULTS

A rapid increase in intrabag volume was observed in all but one subject after both sumatriptan and octreotide administration, while only two subjects exhibited a volume variation after placebo, p<0.01. A significant decrease in the number of phasic contractions was observed after octreotide, while sumatriptan reduced only wave amplitudes (p<0.05). A total of 13 concomitant duodenal phase III-like activities were observed in the duodenum after octreotide, 3 after sumatriptan and 4 after placebo, all followed by spontaneous fundic relaxation with disappearance of phasic contractions, p<0.05. Spontaneous phase III activities were different from phases III-like activities after octreotide in velocity and duration (p<0.05).

CONCLUSIONS

Octreotide induced concomitant fundic relaxation, disappearance of phasic contractions and duodenal phase III-like activity. Sumatriptan relaxed the proximal stomach and reduced the amplitude of fundic phasic contractions without affecting concomitant antroduodenal phase III activity.

Sex differences in regional brain response to aversive pelvic visceral stimuli

To explore sex differences in the response of seven brain regions to an aversive pelvic visceral stimulus, functional magnetic resonance images were acquired from 13 healthy adults (6 women) during 15 s of cued rectal distension at two pressures: 25 mmHg (uncomfortable), and 45 mmHg (mild pain), as well as during an expectation condition (no distension). Random-effects analyses combining subject data voxelwise found 45-mmHg pressure significantly activated the insular and anterior cingulate cortices in both sexes. In men only, the left thalamus and ventral striatum were also activated. Although all activations appeared more extensive in men, no sex difference attained significance. To explore the presence of deactivations, which are generally cancelled by more numerous activations when subjects are combined for each voxel, the number of activated voxels, number of deactivated voxels, and ratio of deactivated voxels to total voxels affected were assessed via random-effects, mixed-model analyses combining subject data at the region level. Greater insula activation in men compared with women was seen during the expectation condition and during the 25-mmHg distension. Greater deactivations in women were seen in the amygdala (25-mmHg distension) and midcingulate (45-mmHg distension). Women had a significantly higher proportion of deactivated voxels than men in all four subcortical structures during 25-mmHg distension. Greater familiarity of females with physiological pelvic visceral discomfort may have enhanced brain systems that dampen arousal networks during lower levels of discomfort.

Role of corticotropin-releasing factor pathways in stress-related alterations of colonic motor function and viscerosensibility in female rodents

BACKGROUND

Clinical reports have shown that irritable bowel syndrome (IBS) is comorbid with anxiety/depression and stress-related events, and that the disorder is more prevalent among women than among men. In rodents, colorectal distention (CRD) induces abdominal contractions, and this visceromotor response is used to assess visceral pain. The activation of brain corticotropin-releasing factor (CRF) pathways has a key role in the behavioral and visceral responses to stress.

OBJECTIVE

In this review of experimental studies that delineate the underlying mechanisms of the stress response, we focused on CRF signaling pathways and sex hormones in modulating visceral hypersensitivity induced by CRD in rodents.

METHODS

The findings of our recent research on the development of an experimental model of visceral pain in female rats and the modulation of the hyperalgesic response to CRD by CRF antagonists were integrated with those of the published literature. A MEDLINE search of the years 1981 to 2005 was conducted using the key words stress, CRF, CRH, CRF1 receptor, IBS, CRD, female rat, visceral pain, estrogen, and anxiety.

RESULTS

CRF and other related mammalian peptides (urocortins) interact with the distinct CRF subtype 1 and 2 receptors. Well-documented preclinical studies have established the role of brain CRF1 receptors in mediating stress-related anxiogenic and visceral (stimulation of colonic motor function and sensitization to repeated CRD) responses in male rodents, whereas more limited studies have been performed in female rats. Our recent study indicated that the CRF1 antagonist antalarmin prevents visceral hypersensitivity induced by 2 sets of CRD in female rats. In several models of visceral pain induced by CRD, sex differences and a sensitization action of estrogen were reported. Our preliminary evidence indicated a potentiating interaction between CRF-CRF1 pathways and estrogen in the stimulation of colonic motor responses that may take place within the enteric neurons of the colon, where both CRF1 and estrogen receptors are present.

CONCLUSIONS

The results of this review suggest that overactivity of CRF1 signaling in the brain and the gut may have relevance in understanding the comorbidity of anxiety/depression and IBS in diarrhea-predominant female patients. Targeting these mechanisms with CRF1 antagonists may provide a novel therapeutic strategy.

Effect of somatostatin analog on postprandial satiation in obesity

OBJECTIVE

Altered satiation may impact postprandial symptoms and potentially change food intake in obesity. Our aim was to compare effects of octreotide and placebo on postprandial symptoms, satiation, and gastric volumes in obesity.

RESEARCH METHODS AND PROCEDURES

In a randomized, parallel-group, double-blind, placebo-controlled study, 26 obese but otherwise healthy participants received 100 mug of octreotide or placebo subcutaneously 30 minutes before each study. Studies were performed on 2 separate days and included validated non-invasive techniques: (99m)Tc-single photon emission computed tomography imaging to measure fasting stomach volume and gastric volume changes after 90 mL of water and 240 mL of Ensure and a standardized nutrient drink test to measure the maximum tolerated volume and postprandial symptoms.

RESULTS

Relative to placebo, octreotide increased gastric volume after 90 mL of water; however, fasting and gastric volume change post-Ensure and maximum tolerated volume of Ensure were not different. Octreotide decreased sensations of fullness (p = 0.035) and bloating (p = 0.05) and tended to reduce aggregate symptoms (p = 0.07) after the fully satiating meal.

DISCUSSION

In obese individuals, somatostatin analog significantly reduced postprandial sensations after a satiating meal without altering maximum tolerated meal volume or postnutrient gastric volume, suggesting an effect on upper gut sensation. The role of somatostatin as a permissive factor in the development of obesity by reducing postprandial sensations deserves further study.

Functional dyspepsia pathogenesis and therapeutic options--implications for management

Functional dyspepsia is far more common than dyspepsia due to organic disease, both in the community and general practice. Proposed aetiopathogenic factors include gastric acid, Helicobacter pylori infection, delayed emptying, hypersensitivity or impaired accommodation of the stomach, dysfunction of the duodenum or brain-gut axis, psychosocial morbidity and post-infective mucosal damage. More effective therapy will depend on the development of drugs targeted at these putative pathophysiological mechanisms. On current evidence tricyclic antidepressants appear to be more effective than either acid suppressants or H. pylori eradication.

Review article: drugs interfering with visceral sensitivity for the treatment of functional gastrointestinal disorders--the clinical evidence

At present, the concept of visceral hypersensitivity provides the leading hypothesis regarding the generation of symptoms in functional gastrointestinal disorders. This paper discusses the current clinical evidence for drugs that have been proposed to interfere with visceral sensitivity in functional gastrointestinal disorders. Several possible pharmacological targets have been identified to reduce visceral pain and to reverse the processes underlying the persistence of visceral hypersensitivity. However, most of the available evidence comes from experimental animal models and cannot simply be extrapolated to patients with functional gastrointestinal disorders. In this review, we selected five drug classes that have been shown to exhibit visceral analgesic properties in experimental studies, and of which data were available regarding their clinical efficacy. These included opioid substances, serotonergic agents, antidepressants, somatostatin analogues and alpha(2)-adrenergic agonists. Although clinical trials show a limited benefit, in particular for serotonergic agents, the evidence illustrating that these effects result from normalization of visceral sensation is currently lacking. Therefore, we conclude that the concept of targeting visceral hypersensitivity as a treatment for functional gastrointestinal disorders is still controversial. Future evaluations require patient selection based on the presence of visceral hypersensitivity and application of compounds that exhibit 'true' viscerosensory effects.

Sensory testing of the esophagus

Originally, sensory testing of the esophagus included the acid perfusion test and the edrophonium test, which were developed to assess patients with non-cardiac chest pain. In the last 2 decades interest in functional esophageal disorders has increased and thus further understanding of the underlying mechanisms of esophageal pain required development of new sensory testing techniques. Balloon distension using a computerized electronic device, electrical stimulation and impedance planimetry have generated important information about esophageal sensory thresholds for pain in different disease states. Intraluminal ultrasonography has been used to determine the physiologic changes of the muscle wall of the esophagus during perception of typical esophageal symptoms. Central evaluation of patients undergoing esophageal stimulation has recently been introduced to assess cerebral activation in different esophageal disorders. However, many studies using esophageal sensory testing are afflicted with significant design flaws, making interpretation of the results very difficult. This is primarily due to lack of recognition of factors that can modulate esophageal sensation.

Anti-hyperalgesic effect of octreotide in patients with irritable bowel syndrome

BACKGROUND

Octreotide has been found to be beneficial in the treatment of chronic pain, although the mechanisms underlying its therapeutic effect are incompletely understood.

AIMS

To assess the effect of octreotide on perceptual responses to rectal distension in irritable bowel syndrome patients and healthy controls at baseline and following the experimental induction of rectal hyperalgesia.

METHODS

In study 1, rectal perception thresholds for discomfort were determined in seven irritable bowel syndrome patients and eight healthy controls on three separate days using a computer-controlled barostat. Subjects received saline, low-dose and high-dose octreotide in a random double-blind fashion. In study 2, perceptual responses to rectal distension were obtained in nine irritable bowel syndrome patients and seven controls before and after repetitive high-pressure mechanical sigmoid stimulation.

RESULTS

Octreotide increased the discomfort thresholds in irritable bowel syndrome patients, but not in controls, without changing rectal compliance. Repetitive sigmoid stimulation resulted in decreased rectal discomfort thresholds in the patient group only. In irritable bowel syndrome patients, octreotide prevented the sensitizing effect of repetitive sigmoid stimulation on rectal discomfort thresholds.

CONCLUSIONS

Octreotide effectively increased discomfort thresholds in irritable bowel syndrome patients, but not in controls, at baseline and during experimentally induced rectal hyperalgesia. These findings suggest that octreotide exerts primarily an anti-hyperalgesic rather than analgesic effect on visceral perception.

Pharmacotherapy for intestinal motor and sensory disorders

Motor disorders of the gastrointestinal tract are characterized by definable impairments of gut contractile function. Other conditions exhibit specific disturbances of visceral afferent and efferent activity, which may underlie selected symptom complexes. Medications in several classes have been developed to treat these disorders of gastrointestinal function. Prokinetic agents are effective therapies for ailments with reduced motor function, whereas antispasmodic drugs reduce symptoms in conditions with exaggerated pressure wave activity. Recently, medications designed to blunt transmission in visceral sensory pathways have been proposed for use in the functional bowel disorders. Finally, some patients may benefit from initiation of nonspecific therapies, which have no appreciable effect on gut motor or sensory function.

Irritable bowel syndrome patients show enhanced modulation of visceral perception by auditory stress

OBJECTIVES

Symptoms in irritable bowel syndrome (IBS) patients are sensitive to psychological stressors. These effects may operate through an enhanced responsiveness of the emotional motor system, a network of brain circuits that modulate arousal, viscerosomatic perception, and autonomic responses associated with emotional responses, including anxiety and anger. The aim of this study was to test the primary hypothesis that IBS patients show altered perceptual responses to rectal balloon distention during experimentally induced psychological stress compared with healthy control subjects.

METHODS

A total of 15 IBS patients (nine women and six men) and 14 healthy controls (seven women and seven men) were studied during two laboratory sessions: 1) a mild stress condition (dichotomous listening to two conflicting types of music), and 2) a control condition (relaxing nature sounds). The stress and relaxation auditory stimuli were delivered over a 10-min listening period preceding rectal distentions and during the rectal distentions but not during the distention rating process. Ratings of intensity and unpleasantness of the visceral sensations, subjective emotional responses, heart rate, and neuroendocrine measures (norepinephrine, cortisol, adrenocorticotropic hormone [ACTH], and prolactin) were obtained during the study.

RESULTS

IBS patients, but not healthy controls, rated the 45-mm Hg visceral stimulus significantly higher in terms of intensity and unpleasantness during the stress condition compared with the relaxation condition. IBS patients also reported higher ratings of stress, anger, and anxiety during the stress compared with the relaxing condition, whereas controls had smaller and nonsignificant subjective responses. Heart rate measurements, but not other neuroendocrine stress measures, were increased under the stress condition in both groups.

CONCLUSION

These findings confirm the hypothesis of altered stress-induced modulation of visceral perception in IBS patients.

Gastrointestinal afferents as targets of novel drugs for the treatment of functional bowel disorders and visceral pain

An intricate surveillance network consisting of enteroendocrine cells, immune cells and sensory nerve fibres monitors the luminal and interstitial environment in the alimentary canal. Functional bowel disorders are characterized by persistent alterations in digestive regulation and gastrointestinal discomfort and pain. Visceral hyperalgesia may arise from an exaggerated sensitivity of peripheral afferent nerve fibres and/or a distorted processing and representation of gut signals in the brain. Novel strategies to treat these sensory bowel disorders are therefore targeted at primary afferent nerve fibres. These neurons express a number of molecular traits including transmitters, receptors and ion channels that are specific to them and whose number and/or behaviour may be altered in chronic visceral pain. The targets under consideration comprise vanilloid receptor ion channels, acid-sensing ion channels, sensory neuron-specific Na(+) channels, P2X(3) purinoceptors, 5-hydroxytryptamine (5-HT), 5-HT(3) and 5-HT(4) receptors, cholecystokinin CCK(1) receptors, bradykinin and prostaglandin receptors, glutamate receptors, tachykinin and calcitonin gene-related peptide receptors as well as peripheral opioid and cannabinoid receptors. The utility of sensory neuron-targeting drugs in functional bowel disorders will critically depend on the compounds' selectivity of action for afferent versus enteric or central neurons.

Postfundoplication Complications in Children

The optimal "treatment" of postfundoplication complications is preoperative prevention of them. Nonreflux causes of the symptom prompting surgery should be carefully eliminated preoperatively. Failure to respond to optimal powerful antireflux pharmacotherapy suggests that GERD was not the cause of symptoms. Neurologic or respiratory disease, delayed gastric emptying or retching, short esophagus, and esophageal dysmotility may predispose patients to complications, and may require careful tailoring of the fundoplication. The optimal antireflux surgery, with a wrap neither too loose nor too tight, may require a nadir lower esophageal sphincter pressure of more than 5 mm Hg to prevent reflux, but less than some value to prevent dysphagia. This latter value may be approximately 10 mm Hg, but depends on swallowing parameters such as peristaltic pressure, lower esophageal sphincter opening diameter, swallowed bolus diameter, and other considerations. Infants may require a gastrostomy tube for venting because of their lower gastric compliance to deal with swallowed air. Children with delayed gastric emptying may benefit from pyloroplasty, but this is debated. When complications occur, re-evaluate the diagnosis and the competence of the fundoplication with barium fluoroscopy, endoscopy with histology, pH probe, and other modalities as indicated. Initially try conservative management of the patient's complications, including dietary and feeding modifications. Give a trial of antireflux pharmacotherapy for recurrent reflux or pharmacotherapy directed at the specific side-effect of the fundoplication if one is present. Consider endoscopically dilating a persistently tight wrap or surgically revising the fundoplication if it is suggested by the evaluation.

Somatostatin sst(2) receptor-mediated inhibition of mesenteric afferent nerves of the jejunum in the anesthetized rat

BACKGROUND & AIMS

Octreotide inhibits visceral sensations in clinical studies, but the site of action and the receptor type(s) involved are unknown. Our aim was to investigate the effects of octreotide, the selective sst(2) receptor agonist (BIM 23027), and the sst(2) antagonist (Cyanamid154806) on the activity of mesenteric afferent fibers innervating the rat jejunum. Their effects were investigated on baseline discharge, mechanosensitivity, and responses to algesic chemicals.

METHODS

Extracellular multiunit recordings of jejunal afferent nerve firing were made in pentobarbitone-anesthetized (60 mg/kg intraperitoneally) male Wistar rats.

RESULTS

Octreotide and BIM23027 (0.001-100 microg/kg intravenously) each evoked a long-lasting inhibition of baseline discharge, which was blocked by cyanamid 154806 (3 mg/kg) and absent in chronically vagotomized animals. Afferent responses to bradykinin were also inhibited by an sst(2) receptor-mediated mechanism but were unaffected by vagotomy. Ramp distentions of the jejunum evoked a biphasic activation of afferent nerve discharge, the low threshold component of which was attenuated in vagotomized animals. Sst(2) receptor agonists significantly inhibited the mechanosensitivity of spinal, but not vagal, afferents.

CONCLUSIONS

These data suggest that activation of somatostatin sst(2) receptors inhibit populations of mesenteric afferents likely to be involved in nociceptive transmission.

Augmented Visceral Perception

Disorders of augmented visceral perception include functional (or nonulcer) dyspepsia and irritable bowel syndrome (IBS). Enhancement of luminal perception can result from alterations in normal elastic gut wall properties or exaggerated responsiveness of visceral sensory nerve pathways. Standard therapies for functional dyspepsia are effective in subsets of patients and may act in part by compensating for gastric hypersensitivity (as with acid-suppressing drugs) or by enhancing gastric compliance (as with some motor-stimulating agents). Likewise, conventional treatments of patients with IBS reduce visceral perception via effects on sensory nerve function (fiber supplements) or luminal wall properties (antispasmodic drugs). Antidepressants are increasingly used in patients with functional dyspepsia or IBS. These drugs have several purported mechanisms, including 1) luminal relaxation, 2) blunting of visceral hypersensitivity, and 3) modulation of central nervous system pain processing pathways. The efficacy of available and investigational agents that act as visceral analgesics or luminal relaxants is an area of intense pharmaceutical research.

Effects of nutrients and serotonin 5-HT3 antagonism on symptoms evoked by distal gastric distension in humans

Distal gastric distension may contribute to meal-related dyspeptic symptoms. This study's aims were to determine the effects of distinct nutrient classes on symptoms induced by distal gastric distension and their dependence on 5-hydroxytryptamine(3) (5-HT3) receptors. Nine healthy subjects rated pain, nausea, and bloating induced by isobaric distal gastric distensions (6-24 mmHg) during duodenal lipid, carbohydrate, protein, or saline perfusion after treatment with placebo or the 5-HT3 receptor antagonist granisetron (10 microg/kg iv). Distensions produced greater pain, nausea, and bloating with lipid at 1.5 kcal/min compared with saline (P < or = 0.02), primarily because of greater distal gastric volumes at each distending pressure. In contrast, carbohydrate and protein had no significant effect. At 3 kcal/min, lipid increased symptoms through a volume-independent as well as a volume-dependent effect. Granisetron did not affect symptom perception or gastric pressure-volume relationships. In conclusion, isobaric distal gastric distension produces more intense symptoms during duodenal lipid compared with saline perfusion. Symptom perception during distal gastric distension is unaffected by 5-HT3 receptor antagonism.

The role of the barostat in human research and clinical practice

BACKGROUND

The barostat is a recently developed device used to study the physiology and pathophysiology of the motor and sensory functions of the gastrointestinal tract. It can monitor volume changes while maintaining a set constant pressure and deliver controlled distensions of gastrointestinal organs. Simultaneously, motility and visceral perception may be assessed. The barostat has contributed to the understanding of physiological processes in the gastrointestinal tract with regard to regulation of tone, compliance, enteric reflexes, sensation and processing of signals to and from the gut. In addition, the barostat has been used to study various gastrointestinal disorders. In functional bowel disorders, objective abnormalities in visceral sensitivity and enteric reflexes have been demonstrated. Numerous other diseases, gastrointestinal in origin as well as systemic diseases affecting the gut, have been studied. In the near future, the barostat may become a clinically useful tool for the objective diagnosis of motor and sensitivity disorders of the gut and for monitoring the effectiveness of therapy.

Octreotide in refractory functional epigastric pain with nutritional impairment--an open study

AIM

To test the therapeutic efficacy of octreotide administered subcutaneously for the relief of chronic refractory epigastric pain severe enough to provoke nutritional impairment.

SUBJECTS AND METHODS

Seventeen patients were enrolled in an open trial. Epigastric pain had lasted from 1 to 8 years (median: 5 years), following anti-reflux surgery in eight patients. Median weight loss was 10% (range 10-15). The initial dose of octreotide was 50 microgram b.d, adjusted during the follow-up visits which were scheduled for months 1, 3, 6, 8, 10, 12 and every 3 months. At each visit, overall symptomatic improvement, frequency and intensity of symptoms were checked on a 10-cm visual analogic scale.

RESULTS

At month 1, a progressive improvement of pain intensity was reported in 15 of the 17 patients, while octreotide was a therapeutic failure in two. In four out of 15, the daily dose of octreotide was increased to 100 microgram b.d. In these 15 patients, median follow-up was 7 months (3-27). The symptomatic benefit was maintained in each patient at month 3, with a median weight gain of 3.5 kg.2-5 An attempt to stop octreotide led to recurrence of symptoms in 2-3 days which were as intense as before the treatment. The 11 patients followed-up for at least 6 months reported persistent improvement of symptoms with octreotide and a median weight gain of 4 kg.3-7 Four patients were followed up for more 11-27 months: octreotide was withdrawn gradually in two who remained asymptomatic. Six of the 17 patients experienced minor side-effects, but none developed biliary sludge.

CONCLUSIONS

This open study suggests that octreotide could be a promising alternative treatment when all others fail in refractory chronic functional epigastric pain severe enough to limit food intake and to induce nutritional impairment. These results must be tested by a placebo-controlled study.

Differential effect of long-term esophageal acid exposure on mechanosensitivity and chemosensitivity in humans

BACKGROUND & AIMS

Chronic tissue injury in the esophagus associated with gastroesophageal reflux disease may result in sensitization of afferent pathways mediating mechanosensitivity and chemosensitivity. The aim of this study was to evaluate the sensitivity to intraluminal acid and to distention of the esophagus in patients with mild-to-moderate gastroesophageal reflux disease.

METHODS

Perceptual responses to intraluminal acid perfusion and to esophageal distention and pressure volume relationships were evaluated in 10 healthy volunteers and in 11 patients. Mechanosensitivity was evaluated with a barostat using unbiased distention protocols and verbal descriptor ratings of sensations. Chemosensitivity to acid was determined at baseline and after a 1-month treatment of acid suppression.

RESULTS

Patients showed enhanced perception of acid perfusion but not of esophageal distension. Chemosensitivity but not mechanosensitivity was correlated with reflux symptoms and with the degree of endoscopically shown tissue injury at baseline. Tissue injury was not associated with altered compliance.

CONCLUSIONS

Mild-to-moderate chronic tissue injury in gastroesophageal reflux disease differentially affects mechanosensitive and chemosensitive afferent pathways. Chronic acid reflux by itself is not likely to play a role in reported esophageal hypersensitivity to distention in patients with noncardiac chest pain.

Effects of somatostatin on proximal gastric motor function and visceral perception

BACKGROUND

Somatostatin affects gastrointestinal motility and secretion and visceral sensation, but little is known about its effects on the proximal stomach.

AIM

To evaluate the effects of somatostatin on proximal gastric motor function and perception of symptoms.

METHODS

Six healthy subjects participated in two experiments performed in random order during continuous intravenous infusion of saline or somatostatin (250 microg/h). Proximal gastric motor function was evaluated using a barostat. We performed pressure and volume distensions and a barostat procedure (minimal distending pressure + 2 mmHg). Symptoms were evaluated at regular intervals using visual analogue scales (VAS).

RESULTS

Neither minimal distending pressure nor gastric fundal tone were significantly different between somatostatin and saline. Pressure-volume curves during distensions were not influenced by somatostatin. However, phasic volume waves were significantly (P < 0.001) reduced by somatostatin, and somatostatin significantly (P < 0.05) reduced symptom perception of fullness and abdominal pressure during stepwise distensions.

Functional gut disorders: from motility to sensitivity disorders. A review of current and investigational drugs for their management

Functional gut disorders include several clinical entities defined on the basis of symptom patterns (e.g., functional dyspepsia, irritable bowel syndrome, functional abdominal pain, functional abdominal bloating), for which there is no established pathophysiological mechanism. Because there is no well-defined pathophysiological target, treatment should be aimed at symptom improvement. Prokinetics and antispasmodics have been widely used in the treatment of functional gut disorders on the assumption that disordered motility is the underlying cause of symptoms, and symptom improvement is indeed achievable with these compounds in some, but not all, patients with features of hypo- or hypermotility, respectively. In the first part of this review, we cover the basic pharmacology and discuss the rationale for the clinical use of prokinetics and antispasmodics. On the other hand, in the past few years, the explosive growth in the research focusing on visceral sensitivity and visceral reflexes has suggested that at least some patients with functional gut disorders have altered visceral perception. Thus, the second part of the review covers these developments and focuses on studies addressing the issue of drugs modulating visceral sensitivity.

Octreotide acts on anorectal physiology: a dynamic study in healthy subjects

BACKGROUND

Somatostatin is localized in the intestinal and pelvic nerves of the anorectum and it seems to act as an important neurotransmitter. However, previous analyses of octreotide (a somatostatin analog) effects on anal function showed conflicting results. By use of a dynamic model in healthy subjects, with comparison to the myogenic effect of glucagon, the aim of our study was to further investigate the pharmacologic targets of octreotide.

METHODS

This was a placebo-controlled, randomized, double-blinded crossover study performed in 12 healthy volunteers who received octreotide, glucagon, or placebo intravenously on separate days. During each sequence, several pressure steps in 3 different protocols of rectal isobaric distension were applied with an electronic barostat. Manometric responses of the anal canal, adaptative volumes, and perception scores of the rectum were recorded.

RESULTS

During both phasic and stepwise distensions, a significant drug effect was encountered at the anal level. Compared with placebo, octreotide significantly increased pressures at both upper and lower levels of the anal canal. In contrast, glucagon decreased pressures at the upper part of the anal canal. Octreotide significantly decreased rectal volumes to phasic distension, but glucagon did not induce any change on rectal adaptation. In addition, neither drug modified perception scores.

CONCLUSION

This study suggests that octreotide acts on reflex arcs and rectal myenteric neurons rather than on anal myogenic targets that respond to glucagon.

Gastrointestinal sensory abnormalities in functional dyspepsia

Symptoms of functional dyspepsia, such as epigastric pain, bloating or early satiety and nausea, are non-specific and are likely to arise from different mechanisms. Current evidence suggests the presence of at least two subgroups: patients who respond to a prolonged course of acid suppression and patients who show a significant overlap of symptoms with other functional gastrointestinal disorders such as irritable bowel syndrome. An enhanced sensitivity of visceral afferent pathways with or without associated autonomic dysregulation appears to play an important role in the aetiology of symptoms in the second group. In the absence of visceral hypersensitivity, neither the slowing of gastric emptying nor the presence of chronic gastritis appears to be sufficient to cause symptoms of functional dyspepsia. The mechanisms and aetiology of visceral hypersensitivity are incompletely understood. An alteration in the interplay between vagal and spinal afferents, and the inadequate activation of antinociceptive systems in response to tissue irritation, may play a role in symptom generation.

Review article: colonic sensorimotor physiology in health, and its alteration in constipation and diarrhoeal disorders

AIM

To review the physiology of colonic motility and sensation in healthy humans and the pathophysiological changes associated with constipation and diarrhoea.

SOURCE

Medline Search from 1965 using the index terms: human, colonic motility, sensation, pharmacology, neurohormonal control, gastrointestinal transit, constipation, diarrhoea and combinations of these.

RESULTS

In health, the ascending and transverse regions of colon function as reservoirs to accommodate ileal chyme and the descending colon acts as a conduit; the neuromuscular functions and transmitters control colonic motility and sensation and play pivotal roles in disorders associated with constipation and/or diarrhoea. Disorders of proximal colonic transit contribute to symptoms in idiopathic constipation, diarrhoea-predominant irritable bowel syndrome and carcinoid diarrhoea. Colonic function in patients presenting with constipation is best assessed clinically by colonic transit time using radiopaque markers ingested orally. Measurements of colonic contractility are less useful clinically but they can help identify motor abnormalities including colonic inertia; in some patients with irritable bowel syndrome, abdominal pain, urgency and diarrhoea are temporally associated with high amplitude contractions, which originate in the proximal colon and traverse the distal conduit at very high propagation velocities. Visceral hypersensitivity contributes to the urgency and tenesmus in irritable bowel syndrome and inflammatory bowel disease. Colonic motility and sensation can be reduced by anticholinergic agents, somatostatin analogues and 5HT3 antagonists.

CONCLUSION

Physiological and pharmacological studies of the human colon have provided new insights into the pathophysiology of colonic disorders, and offer possibilities of novel therapeutic approaches for constipation or diarrhoea associated with colonic motor or sensory dysfunction.

Effect of amitriptyline on symptoms, sleep, and visceral perception in patients with functional dyspepsia

OBJECTIVE

Tricyclic antidepressants in low doses are widely used in the therapy of patients with functional gastrointestinal disorders, yet the mechanism(s) of action of these drugs in these disorders is not known. In the current study, we sought to determine in a group of patients with functional dyspepsia and associated poor sleep how amitryptiline affects digestive symptoms, perceptual responses to gastric distension, and subjective and objective measures of sleep.

METHODS

Patients were randomized to 4 wk of amitryptiline 50 mg taken at bedtime versus placebo. There was a 3-wk washout phase, followed by a cross-over to the alternate treatment. Perceptual sensitivity to gastric distention and sleep EEG were recorded at the end of each treatment period. Diaries of symptoms were maintained throughout.

RESULTS

Seven of seven patients reported significantly less severe gastrointestinal symptoms after 4 wk on amitryptiline compared to placebo. Five of seven patients had evidence for altered perception of gastric balloon distension during placebo. However, the subjective symptom improvement on amitryptiline was not associated with a normalization of the perceptual responses to gastric distension. Baseline sleep dysfunction in the form of reduced sleep efficiency, increased arousal, or abnormal amounts of REM sleep was found in all seven patients. Amitryptiline significantly reduced absolute and relative amounts of REM sleep, but had no effect on sleep parameters related to nonregenerative sleep.

CONCLUSION

The beneficial effect of low dose amitryptiline seen in functional dyspepsia is not related to changes in perception of gastric distension, or to measures of arousal from sleep. An increased tolerance to aversive visceral sensations may play a role in the therapeutic effect.

Effects of octreotide, a somatostatin analogue, on gastric function evaluated by real-time ultrasonography

BACKGROUND

Somatostatin exerts inhibitory effects on physiological functions in the gastrointestinal tract. The actions differ, however, depending on the test meal, dose, and other factors.

AIMS

To determine by use of ultrasonography and scintigraphy the effect of a somatostatin analog, octreotide, on gastric emptying and antral contraction.

SUBJECTS

Twenty healthy men; mean age 23.9 years

METHODS

Subjects were studied for 7 days, once after subcutaneous injection of octreotide, 50 microg, 5 min before the ingestion of a test meal and once after subcutaneous injection of placebo. Ten subjects received a liquid meal, 10 others received a solid meal. With the liquid meal, gastric emptying was measured 15 min after its ingestion and antral contraction was measured for 15 min by ultrasonography. With the solid meal, gastric emptying was measured both by ultrasonography (n = 10) and by simultaneous scintigraphy (n = 6), with antral contraction measured by ultrasonography for 5 h after ingestion of the meal.

RESULTS AND CONCLUSIONS

Octreotide given with a liquid or solid meal inhibited gastric emptying in healthy subjects. A significant suppression of antral contraction occurred only with a solid meal.