GR 38032F (ondansetron), a selective 5HT3 receptor antagonist, slows colonic transit in healthy man

Effects of ondansetron on symptoms during a gastric emptying study and enteral lipid challenge and on daily symptoms in diabetic gastroenteropathy

BACKGROUND

This study compared the effects of ondansetron and placebo in patients with diabetes mellitus and symptoms of dyspepsia (diabetic gastroenteropathy [DGE]).

METHODS

We performed a randomized, double-blinded, placebo-controlled study of ondansetron tablets (8 mg) three times daily for 4 weeks in DGE patients. Symptoms were assessed with the Gastroparesis Cardinal Symptom Index daily diaries. Gastric emptying (GE) of solids (scintigraphy) and duodenal lipid infusions (300 kcal over 2 h) were each assessed twice, with placebo and ondansetron. Drug effects on GE, symptoms during the GE study and during lipid infusion, and daily symptoms were analyzed.

KEY RESULTS

Of 41 patients, 37 completed both GE studies and one completed 1; 31 completed both lipid infusions and four only placebo; and all 35 randomized patients completed 4 weeks of treatment. Compared to placebo, ondansetron reduced the severity of fullness (p = 0.02) and belching (p = 0.049) during lipid infusion but did not affect GE T1/2. Both ondansetron and placebo improved daily symptoms versus the baseline period (p < 0.05), but the differences were not significant. In the analysis of covariance of daily symptoms during the treatment period, the interaction term between treatment and the acute effect of ondansetron on symptoms during lipid challenge was significant (p = .024).

CONCLUSIONS & INFERENCES

Ondansetron significantly reduced fullness during enteral lipid infusion in patients with DGE. Overall, ondansetron did not improve daily symptoms versus placebo. But patients in whom ondansetron improved symptoms during enteral lipid challenge were perhaps more likely to experience symptom relief during daily treatment.

Update on treatment of abdominal pain in irritable bowel syndrome: A narrative review

The objectives of this narrative review are to update readers on the current state-of-the-art regarding diverse approaches for the treatment of pain, global symptoms, or adequate relief in irritable bowel syndrome (IBS). The article appraises medications, dietary interventions including low fermentable oligosaccharides, disaccharides, and monosaccharides and polyols (FODMAP) diet, fecal microbial transplantation (FMT), electrical approaches, and behavioral therapies including cognitive behavioral therapy (CBT), gut-directed hypnotherapy (GDH), mindfulness, and open-label placebo. Current evidence demonstrates only modest benefit in global IBS symptoms and pain relief. A future approach that identifies pathophysiological mechanisms of IBS through validated biomarkers has the potential to individualize treatment of patients rather than sequential therapeutic trial and error approaches.

Diurnal changes of colonic motility and regulatory factors for colonic motility in Suncus murinus

BACKGROUND

The aim of this study was to investigate the fundamental mechanisms of colonic motility in the house musk suncus (Suncus murinus) as an established animal model of gut motility.

METHODS

To measure gut motility in free-moving conscious suncus, strain gauge force transducers were implanted on the serosa of the colon and gastric body.

KEY RESULTS

We recorded diurnal changes in colonic motility and observed the relationship between feeding and colonic motility. Giant migrating contractions (GMCs) of the colon were invariably detected during defecation and tended to increase during the dark period, thereby indicating that colonic motility has a circadian rhythm. Given that GMCs in the suncus were observed immediately after feeding during the dark period, we assume the occurrence of a gastrocolic reflex in suncus, similar to that observed in humans and dogs. We also examined the factors that regulate suncus GMCs. Intravenous administration of 5-HT (100 µg/kg), substance P (10 and 100 µg/kg), calcitonin gene-related peptide (10 µg/kg), and α2 adrenergic receptor antagonist yohimbine (0.5, 1, and 3 mg/kg) induced GMC-like contractions, as did intragastric and intracolonic administration of the transient receptor potential vanilloid 1 agonist, capsaicin (1 mg/kg).

CONCLUSIONS & INFERENCES

These results indicate that the fundamental mechanisms of colonic motility in suncus are similar to those in humans and dogs, and we thus propose that suncus could serve as a novel small animal model for studying colonic motility.

Tapping into 5-HT3 Receptors to Modify Metabolic and Immune Responses

5-hydroxytryptamine type 3 (5-HT₃) receptors are ligand gated ion channels, which clearly distinguish their mode of action from the other G-protein coupled 5-HT or serotonin receptors. 5-HT₃ receptors are well established targets for emesis and gastrointestinal mobility and are used as adjunct targets in treating schizophrenia. However, the distribution of these receptors is wider than the nervous system and there is potential that these additional sites can be targeted to modulate inflammatory and/or metabolic conditions. Recent progress in structural biology and pharmacology of 5-HT₃ receptors have provided profound insights into mechanisms of their action. These advances, combined with insights into clinical relevance of mutations in genes encoding 5-HT₃ subunits and increasing understanding of their implications in patient's predisposition to diseases and response to the treatment, open new avenues for personalized precision medicine. In this review, we recap on the current status of 5-HT₃ receptor-based therapies using a biochemical and physiological perspective. We assess the potential for targeting 5-HT₃ receptors in conditions involving metabolic or inflammatory disorders based on recent findings, underscoring the challenges and limitations of this approach.

Identification and molecular study on the interaction of Schisandrin C with human 5-HT3A receptor

Schisandrin C (Sch C) is one of the main components of Schisandra chinensis (Schisandra). Since the olden times, Schisandra has been used as a traditional herbal medicine in Asia. Recent studies have shown that Schisandra is effective against irritable bowel syndrome (IBS) in an animal model and affects IBS through the 5-HT_3A pathway in the IBS rat model. However, there lacks fundamental research on the interaction of specific components of Schisandra with the 5-HT_3A receptor for the treatment of IBS. We hypothesized that a component of Schisandra binds to the 5-HT_3A receptor and identified Sch C via a screening work using two electrode-voltage clamps (TEVC). Thus, we aimed to elucidate the neuropharmacological actions between Sch C and the 5-HT_3A receptor at molecular and cellular levels. Co-treatment of Sch C with 5-HT inhibited I_5-HT in a reversible, concentrate-dependent, like-competition, and voltage-independent manner, and IC₅₀ values of Sch C. Besides, the main binding positions of Sch C were identified through 3D modeling and point mutation were V225A and V288Y on 5-HT_3A receptor. Thus, we suggest the potential of Sch C in treating IBS in a manner that suppresses excessive neuronal serotonin signaling in the synapse of sensory neurons and enterochromaffin (EC) cells. In conclusion, the results demonstrate the mechanism of interaction between Sch C and 5-HT_3A receptor and reveal Sch C as a novel antagonist.

Does Intravenous Ondansetron Affect the Intestinal Motility Pattern in Healthy Donkeys (Equus asinus)?

The current study was undertaken to investigate the effect of intravenous administration of ondansetron on the small and large intestinal motility in donkeys (Equus asinus) using non-invasive transabdominal ultrasonography. The current prospective, randomized, placebo-controlled, crossover study was conducted on thirty healthy donkeys (15 males and 15 females). The selected donkeys underwent two trials; the first was performed by intravenous administration of saline solution as a placebo, while the second was carried out by intravenous administration of ondansetron hydrochloride. The contractility of selected portions of both the small intestine (duodenum and jejunum) and the large intestine (left colon, right colon, and cecum) was counted over a period of 3 minutes before administration (zero time) and at 15, 30, 60, 90, 120, 180, and 240 minutes after administration. The results of this study showed that ondansetron significantly altered the small and large intestinal contractility compared to normal saline. Intravenous administration of ondansetron induced a significant decrease in the duodenal, jejunal and cecal contractility compared to placebo at 30, 60, 90, and 120 minutes after administration. Likewise, ondansetron induced a significant decrease in the left colon and right colon contractility when compared with placebo at 30, 60, 90, 120, and 180 minutes following administration. Ondansetron can be used as a highly specific and selective serotonin 5-HT₃ receptor antagonist for reducing the small and large intestinal motility in donkeys, and is therefore highly suggested for treating spasmodic colic in equine.

Implications of Breast Cancer Chemotherapy-Induced Inflammation on the Gut, Liver, and Central Nervous System

Breast Cancer is still one of the most common cancers today; however, with advancements in diagnostic and treatment methods, the mortality and survivorship of patients continues to decrease and increase, respectively. Commonly used treatments today consist of drug combinations, such as doxorubicin and cyclophosphamide; docetaxel, doxorubicin, and cyclophosphamide; or doxorubicin, cyclophosphamide, and paclitaxel. Although these combinations are effective at destroying cancer cells, there is still much to be understood about the effects that chemotherapy can have on normal organ systems such as the nervous system, gastrointestinal tract, and the liver. Patients can experience symptoms of cognitive impairments or “chemobrain”, such as difficulty in concentrating, memory recollection, and processing speed. They may also experience gastrointestinal (GI) distress symptoms such as diarrhea and vomiting, as well as hepatotoxicity and long term liver damage. Chemotherapy treatment has also been shown to induce peripheral neuropathy resulting in numbing, pain, and tingling sensations in the extremities of patients. Interestingly, researchers have discovered that this array of symptoms that cancer patients experience are interconnected and mediated by the inflammatory response.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Relationship Between the Gut Microbiome and Systemic Chemotherapy

The intestinal microbiome encodes vast metabolic potential, and multidisciplinary approaches are enabling a mechanistic understanding of how bacterial enzymes impact the metabolism of diverse pharmaceutical compounds, including chemotherapeutics. Microbiota alter the activity of many drugs and chemotherapeutics via direct and indirect mechanisms; some of these alterations result in changes to the drug's bioactivity and bioavailability, causing toxic gastrointestinal side effects. Gastrointestinal toxicity is one of the leading complications of systemic chemotherapy, with symptoms including nausea, vomiting, diarrhea, and constipation. Patients undergo dose reductions or drug holidays to manage these adverse events, which can significantly harm prognosis, and can result in mortality. Selective and precise targeting of the gut microbiota may alleviate these toxicities. Understanding the composition and function of the microbiota may serve as a biomarker for prognosis, and predict treatment efficacy and potential adverse effects, thereby facilitating personalized medicine strategies for cancer patients.

Treatment of irritable bowel syndrome with diarrhoea using titrated ondansetron (TRITON): study protocol for a randomised controlled trial

BACKGROUND

Irritable bowel syndrome with diarrhoea (IBS-D) affects up to 4% of the general population. Symptoms include frequent, loose, or watery stools with associated urgency, resulting in marked reduction of quality of life and loss of work productivity. Ondansetron, a 5HT3 receptor antagonist, has had an excellent safety record for over 20 years as an antiemetic, yet is not widely used in the treatment of IBS-D. It has, however, been shown to slow colonic transit and in a small randomised, placebo-controlled, cross-over pilot study, benefited patients with IBS-D.

METHODS

This trial is a phase III, parallel group, randomised, double-blind, multi-centre, placebo-controlled trial, with embedded mechanistic studies. Participants (n = 400) meeting Rome IV criteria for IBS-D will be recruited from outpatient and primary care clinics and by social media to receive either ondansetron (dose titrated up to 24 mg daily) or placebo for 12 weeks. Throughout the trial, participants will record their worst abdominal pain, worst urgency, stool frequency, and stool consistency on a daily basis. The primary endpoint is the proportion of "responders" in each group, using Food and Drug Administration (FDA) recommendations. Secondary endpoints include pain intensity, stool consistency, frequency, and urgency. Mood and quality of life will also be assessed. Mechanistic assessments will include whole gut transit, faecal tryptase and faecal bile acid concentrations at baseline and between weeks 8 and 11. A subgroup of participants will also undergo assessment of sensitivity (n = 80) using the barostat, and/or high-resolution colonic manometry (n = 40) to assess motor patterns in the left colon and the impact of ondansetron.

DISCUSSION

The TRITON trial aims to assess the effect of ondansetron across multiple centres. By defining ondansetron's mechanisms of action we hope to better identify patients with IBS-D who are likely to respond.

TRIAL REGISTRATION

ISRCTN, ISRCTN17508514 , Registered on 2 October 2017.

Effects of Clozapine on the Gut: Cross-Sectional Study of Delayed Gastric Emptying and Small and Large Intestinal Dysmotility

BACKGROUND

Gastrointestinal hypomotility in people taking clozapine is common, poorly understood and potentially dangerous. It causes distress and sometimes sudden death, with greater associated morbidity than the better known adverse effect of clozapine, agranulocytosis. Neither the mechanism nor prevalence of clozapine-induced gastrointestinal hypomotility is well understood. Previous studies show clozapine impedes colon transit, likely owing to anticholinergic and anti-serotonergic properties. However, regional gastrointestinal transit times (including gastric and small bowel emptying) have not been quantified.

METHODS

We used wireless motility capsules to measure gastric emptying and small and large bowel transit times in clozapine-treated individuals. We tested 17 clozapine-treated patients without any known gastrointestinal dysfunction, and compared data with matched normative transit times.

RESULTS

Clozapine-treated participants had significant 'slow gut', with dysmotility in at least one region of the gastrointestinal tract evident in 82%, with 59% experiencing multi-regional dysmotility. Delayed gastric emptying was diagnosed in 41%, delayed small bowel transit in 71% and delayed colon transit in 50%. Only 18% of participants had normal studies. Hypomotility was not correlated with ethnicity, sex or duration of treatment. Subjective reporting of constipation had low sensitivity in predicting dysmotility. Delayed gastric emptying had been unrecognised clinically for all participants.

CONCLUSION

Clozapine is associated with significant multi-regional gastrointestinal dysfunction. This is relevant when considering the relationship between clozapine use and conditions such as gastroparesis, choking, aspiration pneumonia, constipation, ileus and intestinal pseudo-obstruction. While the constipating properties of clozapine are now well recognised, this study shows a high degree of vigilance is required for both lower and upper gastrointestinal dysmotility in people taking this antipsychotic.

A prospective study of palonosetron for prevention of chemotherapy-induced nausea and vomiting in malignant lymphoma patients following highly emetogenic chemotherapy

BACKGROUND

Chemotherapy-induced nausea and vomiting (CINV) is a troublesome issue in chemotherapy for cancer patients. A second-generation 5HT₃ receptor antagonist (5HT₃RA), palonosetron, is effective and safe for the prevention of CINV in breast cancer patients treated with cyclophosphamide and anthracycline, but there is little data for malignant lymphoma. We conducted a prospective phase 2 study at a single institution to clarify the efficacy and safety of palonosetron in lymphoma patients.

METHODS

Chemotherapy-naïve lymphoma patients who were treated with highly emetogenic chemotherapy (HEC) received a single intravenous bolus of palonosetron, 0.75 mg/body, before chemotherapy on day 1 during the first course of chemotherapy. The occurrence of CINV was assessed using the Multinational Association for Supportive Care in Cancer (MASCC) antiemesis tool, which was recorded by patients during the first course of chemotherapy.

RESULTS

A total of 59 patients were enrolled, and 49 patients were eligible and evaluated. The complete response (CR) rate was 93.9% (95% confidence interval 83.1-98.7%) at 0-120 h post-chemotherapy. The proportion of patients who developed nausea of any grade and vomiting at 0-120 h post-chemotherapy was 34.7 and 6.1%, respectively. Although treatment-related adverse events were observed in 36 (73.5%) patients, these were mild and they recovered by the next cycle of chemotherapy.

CONCLUSION

The present study demonstrated that a single dose of palonosetron was highly effective and safe for the prevention of CINV in lymphoma patients.

Irritable Bowel Syndrome: Pathophysiology and Current Therapeutic Approaches

Irritable bowel syndrome (IBS) is a prevalent condition affecting 10-20% of adults in most countries; IBS results in significant morbidity and health care costs. IBS is a disorder of the brain-gut axis, and recent insights into the pathophysiological mechanisms include altered bile acid metabolism, neurohormonal regulation, immune dysfunction, alterations in the epithelial barrier, and secretory properties of the gut. There remains a significant unmet need for effective treatments, particularly for the pain component of IBS, although the introduction of drugs directed at secretion, motility, and a nonabsorbable antibiotic provides an option for the bowel dysfunction in IBS.

Rotavirus and Serotonin Cross-Talk in Diarrhoea

Rotavirus (RV) has been shown to infect and stimulate secretion of serotonin from human enterochromaffin (EC) cells and to infect EC cells in the small intestine of mice. It remains to identify which intracellularly expressed viral protein(s) is responsible for this novel property and to further establish the clinical role of serotonin in RV infection. First, we found that siRNA specifically silencing NSP4 (siRNA^NSP4) significantly attenuated secretion of serotonin from Rhesus rotavirus (RRV) infected EC tumor cells compared to siRNA^VP4, siRNA^VP6 and siRNA^VP7. Second, intracellular calcium mobilization and diarrhoeal capacity from virulent and avirulent porcine viruses correlated with the capacity to release serotonin from EC tumor cells. Third, following administration of serotonin, all (10/10) infants, but no (0/8) adult mice, responded with diarrhoea. Finally, blocking of serotonin receptors using Ondansetron significantly attenuated murine RV (strain EDIM) diarrhoea in infant mice (2.9 vs 4.5 days). Ondansetron-treated mice (n = 11) had significantly (p < 0.05) less diarrhoea, lower diarrhoea severity score and lower total diarrhoea output as compared to mock-treated mice (n = 9). Similarly, Ondansetron-treated mice had better weight gain than mock-treated animals (p < 0.05). A most surprising finding was that the serotonin receptor antagonist significantly (p < 0.05) also attenuated total viral shedding. In summary, we show that intracellularly expressed NSP4 stimulates release of serotonin from human EC tumor cells and that serotonin participates in RV diarrhoea, which can be attenuated by Ondansetron.

Pharmacologic Therapies in Gastrointestinal Diseases

Several key areas in gastroenterology pharmacotherapy are rapidly evolving, including the treatment of hepatitis C virus (HCV), irritable bowel syndrome, gastroesophageal reflux disease (GERD) and peptic ulcer disease. HCV treatment has radically changed in the past 2 years and now most patients are treatment candidates and have a high likelihood of permanent cure. Pharmacotherapy is now first-line treatment for patients with moderate to severe symptoms of irritable bowel syndrome. Proton pump inhibitors (PPIs) are the mainstay of therapy in gastric and duodenal ulcers and GERD, although long-term use carries the risk of several side effects that should be considered.

Pharmacological, Pharmacokinetic, and Pharmacogenomic Aspects of Functional Gastrointestinal Disorders

This article reviews medications commonly used for the treatment of patients with functional gastrointestinal disorders. Specifically, we review the animal models that have been validated for the study of drug effects on sensation and motility; the preclinical pharmacology, pharmacokinetics, and toxicology usually required for introduction of new drugs; the biomarkers that are validated for studies of sensation and motility endpoints with experimental medications in humans; the pharmacogenomics applied to these medications and their relevance to the FGIDs; and the pharmacology of agents that are applied or have potential for the treatment of FGIDs, including psychopharmacologic drugs.

The clinical potential of ramosetron in the treatment of irritable bowel syndrome with diarrhea (IBS-D)

Irritable bowel syndrome (IBS) is a highly prevalent functional bowel disorder. Serotonin (5-HT) is known to play a physiological and pathophysiological role in the regulation of gastrointestinal function. In experimental studies, 5-HT3 receptor antagonists have been reported to slow colon transit, to blunt gastrocolonic reflex, and to reduce rectal sensitivity. Alosetron and cilansetron, potent and selective 5-HT3 receptor antagonists, have proven efficacy in the treatment of IBS with diarrhea (IBS-D). However, alosetron was voluntarily withdrawn due to postmarketing reports of ischemic colitis and complications of constipation, and cilansetron was never marketed. Currently alosetron is available under a risk management program for women with severe IBS-D. Ramosetron is another potent and selective 5-HT3 receptor antagonist, which has been marketed in Japan, South Korea, and Taiwan. In animal studies, ramosetron reduced defecation induced by corticotrophin-releasing hormone and had inhibitory effects on colonic nociception. In two randomized controlled studies including 957 patients with IBS-D, ramosetron increased monthly responder rates of patient-reported global assessment of IBS symptom relief compared with placebo. Ramosetron was also as effective as mebeverine in male patients with IBS-D. In a recent randomized controlled trial with 343 male patients with IBS-D, ramosetron has proved effective in improving stool consistency, relieving abdominal pain/discomfort, and improving health-related quality of life. Regarding safety, ramosetron is associated with a lower incidence of constipation compared with other 5-HT3 receptor antagonists and has not been associated with ischemic colitis. Although further large prospective studies are needed to assess whether ramosetron is effective for female patients with IBS-D and to evaluate its long-term safety, ramosetron appears to be one of the most promising agents for patients with IBS-D.

Crosstalk at the mucosal border: importance of the gut microenvironment in IBS

The aetiology and pathology of IBS, a functional bowel disorder thought to lack an organic cause, is largely unknown. However, studies suggest that various features, such as altered composition of the gut microbiota, together with increased intestinal permeability, a changed balance in the enteroendocrine system and a dysregulated immune system in the gut, most likely have an important role in IBS. Exactly how these entities act together and give rise to symptoms is still unknown, but an altered gut microbiota composition could lead to dysregulation of the intestinal barrier as well as the enteroendocrine and the immune systems, which (through interactions with the nervous system) might generate symptoms. This Review highlights the crosstalk between the gut microbiota, the enteroendocrine system, the immune system and the role of intestinal permeability in patients with IBS.

Current and emerging drug options in the treatment of diarrhea predominant irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome diarrhea predominant (IBS-D) is a highly prevalent GI disease, affecting nearly a third of all patients diagnosed with irritable bowel syndrome. Current treatment options are limited.

AREAS COVERED

This review discusses the pharmacotherapeutic options for IBS-D including currently used medications, the two newly FDA approved medications, as well as emerging therapies with potential benefit in IBS-D. Particular emphasis is placed on rifaximin and eluxadoline and their possible use in IBS-D.

EXPERT OPINION

Current pharmacological treatment of IBS-D includes loperamide, bile acid sequestrants, antispasmodics, tricyclic antidepressants, alosetron, eluxadoline and rifaximin. The latter two treatments have significantly added to the pharmacotherapeutic options for patients suffering from IBS-D.

Intestinal obstruction in pregnancy by ondansetron

BACKGROUND

Ondansetron use for nausea and vomiting during pregnancy has increased in the last years, although its maternal and fetal safety is not conclusive.

CASE

We describe a case of intestinal obstruction in a pregnant woman with severe nausea and vomiting of pregnancy treated with ondansetron, which is known to slow gut motility.

CONCLUSION

The spontaneous reporting system of WHO confirms that this potentially life threatening complication is more common than what the peer review literature may suggest and needs to be looked into carefully, especially in view of the wide spread off-label use for NVP.

Metabolic kinetics of 5-hydroxytryptamine and the research targets of functional gastrointestinal disorders

5-Hydroxytryptamine (5-HT) is an important neurotransmitter in both the central and enteric nervous systems. It has diverse functions in regulating gastrointestinal motility and visceral sensitivity, emotion, appetite, pain and sensory perception, cognition, sexual activity and sleep. These functions are mainly associated with the metabolic kinetics of 5-HT in different tissues. Tryptophan hydroxylase is the rate-limiting enzyme and modulates serotonin synthesis. Vesicular monoamine transporter 1 plays a role in 5-HT storage and release. Degradation of 5-HT is mediated by monoamine oxidase-A. All these factors influence the action of 5-HT in vivo. Functional gastrointestinal disorders (FGIDs) are characterized by a series of symptoms including abdominal pain, diarrhea, constipation, anxiety and depression, in the absence of identifiable structural or biochemical abnormalities. They are frequently accompanied by changed gut motility or visceral sensitivity. An increasing body of research has found FGIDs to be closely associated with 5-HT, and drugs such as citalopram, paroxetine, venlafaxine, alosetron, tegaserod, prucalopride and mosapride have all been developed or discovered from the perspective of the metabolic kinetics of 5-HT. This review discusses the relationship between the metabolic kinetics of 5-HT and research targets in the field of FGIDs and suggests areas of future study that may be useful for understanding these disorders and identification of potential therapeutic targets.

A randomised trial of ondansetron for the treatment of irritable bowel syndrome with diarrhoea

BACKGROUND

Irritable bowel syndrome with diarrhoea (IBS-D) is particularly debilitating due to urgency and episodic incontinence. Some 5-hydroxytryptamine 3 (5-HT3) receptor antagonists (5-HT3RAs) have proven effective but have serious side effects. Ondansetron, also a 5-HT3RA, has been widely used as an antiemetic with an excellent safety record for over two decades. Our aim was to assess its effectiveness in IBS-D.

METHODS

120 patients meeting Rome III criteria for IBS-D entered a randomised, double-blind, placebo-controlled crossover study of 5 weeks of ondansetron 4 mg versus placebo with dose titration allowed, up to two tablets three times daily in the first 3 weeks. Patients completed daily diaries documenting stool consistency using the Bristol Stool Form score. Gut transit was measured in the last week of each treatment. The primary endpoint was average stool consistency in the last 2 weeks of treatment.

RESULTS

Ondansetron significantly improved stool consistency (mean difference in stool form between ondansetron and placebo -0.9, 95% CI -1.1 to -0.6, p<0.001). Compared with placebo, patients on ondansetron experienced fewer days with urgency (p<0.001), lower urgency scores (p<0.001), reduced frequency of defaecation (p=0.002) and less bloating (p=0.002), although pain scores did not change significantly. IBS symptom severity score fell more with ondansetron than placebo (83±9.8 vs 37±9.7, p=0.001). 65% reported adequate relief with ondansetron but not placebo compared with 14% reporting relief with placebo but not ondansetron, relative risk 4.7, 95% CI 2.6 to 8.5, p<0.001.

CONCLUSIONS

Ondansetron relieves some of the most intrusive symptoms of IBS-D, namely loose stools, frequency and urgency.

Effects of 5-HT2B, 5-HT3 and 5-HT4 receptor antagonists on gastrointestinal motor activity in dogs

AIM: To study the effects of 5-hydroxytryptamine (5-HT) receptor antagonists on normal colonic motor activity in conscious dogs.

METHODS: Colonic motor activity was recorded using a strain gauge force transducer in 5 dogs before and after 5-HT2B, 5-HT3 and 5-HT4 receptor antagonist administration. The force transducers were implanted on the serosal surfaces of the gastric antrum, terminal ileum, ileocecal sphincter and colon. Test materials or vehicle alone was administered as an intravenous bolus injection during a quiescent period of the whole colon in the interdigestive state. The effects of these receptor antagonists on normal gastrointestinal motor activity were analyzed.

RESULTS: 5-HT2B, 5-HT3 and 5-HT4 receptor antagonists had no contractile effect on the fasting canine terminal ileum. The 5-HT3 and 5-HT4 receptor antagonists inhibited phase III of the interdigestive motor complex of the antrum and significantly inhibited colonic motor activity. In the proximal colon, the inhibitory effect was dose dependent. Dose dependency, however, was not observed in the distal colon. The 5-HT2B receptor antagonist had no contractile effect on normal colonic motor activity.

CONCLUSION: The 5-HT3 and 5-HT4 receptor antagonists inhibited normal colonic motor activity. The 5-HT2B receptor antagonist had no contractile effect on normal colonic motor activity.

Serotonin signalling in the gut--functions, dysfunctions and therapeutic targets

Serotonin (5-HT) has been recognized for decades as an important signalling molecule in the gut, but it is still revealing its secrets. Novel gastrointestinal functions of 5-HT continue to be discovered, as well as distant actions of gut-derived 5-HT, and we are learning how 5-HT signalling is altered in gastrointestinal disorders. Conventional functions of 5-HT involving intrinsic reflexes include stimulation of propulsive and segmentation motility patterns, epithelial secretion and vasodilation. Activation of extrinsic vagal and spinal afferent fibres results in slowed gastric emptying, pancreatic secretion, satiation, pain and discomfort, as well as nausea and vomiting. Within the gut, 5-HT also exerts nonconventional actions such as promoting inflammation and serving as a trophic factor to promote the development and maintenance of neurons and interstitial cells of Cajal. Platelet 5-HT, originating in the gut, promotes haemostasis, influences bone development and serves many other functions. 5-HT3 receptor antagonists and 5-HT4 receptor agonists have been used to treat functional disorders with diarrhoea or constipation, respectively, and the synthetic enzyme tryptophan hydroxylase has also been targeted. Emerging evidence suggests that exploiting epithelial targets with nonabsorbable serotonergic agents could provide safe and effective therapies. We provide an overview of these serotonergic actions and treatment strategies.

Evolving ideas about the male refractory period

The male refractory period (MRP) continues to be a topic of discussion and debate within the field of sexual medicine. To date explanations rely on central descending (efferent) influences involving specific neurotransmitter systems. Herein we explore the issue of the male refractory period, identifying problems with current explanations, specifying the parameters of an adequate model, and suggesting possible mechanisms mediating this phenomenon. We review the literature regarding existing explanations for the MRP and look to other systems of physiological regulation that might provide a model for the conceptualization of the MRP. Our approach differs from traditional explanations in that it emphasizes the possible roles of various peripheral, rather than central, feedback (afferent) systems that affect peripheral autonomic functioning and response. Yet our approach is consistent with other peripheral regulatory feedback systems controlling autonomic response related to such processes as heart rate, respiration, and gut motility. Although direct empirical research supporting our approach is lacking, sufficient evidence exists to support the idea that such processes are not only possible but likely with respect to the male refractory period. We suggest several lines of research that might provide empirical support for this approach.

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.

The effects of 5-HT4 receptor agonist, mosapride citrate, on visceral hypersensitivity in a rat model

BACKGROUND AND AIMS

Mosapride citrate is known to affect gastric motility. However, whether mosapride citrate has any effect on visceral pain in the colon or rectum is not certain. The aim of this study was to assess the effects of mosapride citrate on visceral pain in a rat visceral hypersensitivity model.

METHODS

The perception of visceral pain was evaluated by the visceromotor response to colorectal distension observed on electromyographs of the abdominal musculature in urethane-anesthetized rats. Visceral hypersensitivity was induced by the intrarectal instillation of 4% acetic acid or 1.5% zymosan. Mosapride citrate was administered intraperitoneally 3 h later. VMRs to CRD were recorded prior to the instillation of acetic acid or zymosan and before and after mosapride citrate treatment.

RESULTS

The intracolonic instillation of acetic acid resulted in a significant increase in VMRs of the abdominal muscles to CRD, compared with the pretreatment state (174 ± 24%, P < 0.05). The intracolonic instillation of zymosan resulted in a significant increase in VMRs of the abdominal muscles to CRD, compared with the pretreatment state (144 ± 9%, P < 0.05). Intraperitoneal injection of mosapride citrate resulted in a significant reduction in the VMRs to CRD in an acetic acid-induced visceral hypersensitivity rat model (61 ± 9%, P < 0.05). The intraperitoneal injection of mosapride citrate also resulted in a significant reduction in the VMRs to CRD in a zymosan-induced visceral hypersensitivity rat model (67 ± 9%, P < 0.05).

CONCLUSIONS

Mosapride citrate diminished visceral pain in rats.

Pharmacologic and complementary and alternative medicine therapies for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by episodic abdominal pain or discomfort in association with altered bowel habits (diarrhea and/or constipation). Other gastrointestinal symptoms, such as bloating and flatulence, are also common. A variety of factors are believed to play a role in the development of IBS symptoms, including altered bowel motility, visceral hypersensitivity, psychosocial stressors, altered brain-gut interactions, immune activation/low grade inflammation, alterations in the gut microbiome, and genetic factors. In the absence of biomarkers that can distinguish between IBS subgroups on the basis of pathophysiology, treatment of this condition is predicated upon a patient's most bothersome symptoms. In clinical trials, effective therapies have only offered a therapeutic gain over placebos of 7-15%. Evidence based therapies for the global symptoms of constipation predominant IBS (IBS-C) include lubiprostone and tegaserod; evidence based therapies for the global symptoms of diarrhea predominant IBS (IBS-D) include the probiotic Bifidobacter infantis, the nonabsorbable antibiotic rifaximin, and alosetron. Additionally, there is persuasive evidence to suggest that selected antispasmodics and antidepressants are of benefit for the treatment of abdominal pain in IBS patients. Finally, several emerging therapies with novel mechanisms of action are in development. Complementary and alternative medicine therapies including probiotics, herbal therapies and acupuncture are gaining popularity among IBS sufferers, although concerns regarding manufacturing standards and the paucity of high quality efficacy and safety data remain.

Peripherally acting therapies for the treatment of irritable bowel syndrome

Gut-acting therapies are common therapies for irritable bowel syndrome (IBS). Most of these peripheral acting agents are primarily targeted at individual symptoms. The evidence supporting the use of these agents in IBS is largely anecdotal. Serotonergic agents and the chloride channel activator lubiprostone have shown efficacy in treating symptoms of IBS. The clinical evidence supporting the use of these agents is based on data from high-quality clinical trials. The use of serotonergic agents for IBS in the United States is limited to the 5-hydroxytryptamine-3 antagonist alosetron in the treatment of women with severe IBS with diarrhea refractory to traditional therapy.

Effects of a 5-HT(3) antagonist, ondansetron, on fasting and postprandial small bowel water content assessed by magnetic resonance imaging

BACKGROUND

5-HT(3) antagonists have been shown to be effective in relieving the symptoms of irritable bowel syndrome with diarrhoea (IBS-D). Using a recently validated magnetic resonance imaging (MRI) method, we have demonstrated reduced fasting small bowel water content (SBWC) in IBS-D associated with accelerated small bowel transit. We hypothesized that slowing of transit with ondansetron would lead to an increase in SBWC by inhibiting fasting motility.

AIM

To assess the effects of ondansetron compared with placebo in healthy volunteers on SBWC and motility in two different groups of subjects, one studied using MRI and another using manometry.

METHODS

Healthy volunteers were given either a placebo or ondansetron on the day prior to and on the study day. Sixteen volunteers underwent baseline fasting and postprandial MRI scans for 270 min. In a second study, a separate group of n = 18 volunteers were intubated and overnight migrating motor complex (MMC) recorded. Baseline MRI scans were carried out after the tube was removed.

RESULTS

Fasting SBWC was markedly increased by ondansetron (P < 0.0007). Ondansetron reduced the overall antroduodenal Motility Index (P < 0.04). The subjects who were intubated had significantly lower fasting SBWC (P < 0.0002) compared with the group of subjects who were not intubated.

CONCLUSIONS

The 5-HT(3) receptor antagonism increased fasting small bowel water. This was associated with reduced fasting antroduodenal Motility Index which may explain the clinical benefit of such drugs.

Current insights in to the pathophysiology of Irritable Bowel Syndrome

Irritable Bowel Syndrome (IBS) represents a functional disorder of gastrointestinal tract without the presence of an anatomic defect, in which abdominal pain is relieved with defecation and is associated with altered bowel habits.

IBS includes a wide range of symptoms while its pathophysiology is very complicated. Recent studies indicate that the most important mechanisms include visceral sensitivity, abnormal gut motility and autonomous nervous system dysfunction. The interactions between these three mechanisms make bowel's function susceptible to many exogenous and endogenous factors like gastrointestinal flora, feeding and psychosocial factors. Recent data indicate that according to the above mechanisms, the influence of genetic factors and polymorphisms of human DNA in the development of IBS is equally important.

5-Hydroxytryptamine Receptor Subtypes and their Modulators with Therapeutic Potentials

5-hydroxytryptamine (5-HT) has become one of the most investigated and complex biogenic amines. The main receptors and their subtypes, e.g., 5-HTI (5-HT1A, 5-HT1B, 5-HTID, 5-HTIE and 5-HT1F), 5-HT2 (5-HT2A, 5-HT2B and 5-HT2C), 5-HT3, 5-HT4, 5-HT5 (5-HT5A, 5-HT5B), 5-HT6 and 5-HT7 have been identified. Specific drugs which are capable of either selectively stimulating or inhibiting these receptor subtypes are being designed. This has generated therapeutic potentials of 5-HT receptor modulators in a variety of disease conditions. Conditions where 5-HT receptor modulators have established their use with distinct efficacy and advantages include migraine, anxiety, psychosis, obesity and cancer therapy-induced vomiting by cytotoxic drugs and radiation. Discovery of 5-HT, its biosynthesis, metabolism, physiological role and the potential of 5-HT receptor modulators in various nervous, cardiovascular and gastrointestinal tract disorders, bone growth and micturition have been discussed in this article.

Inhibition of colonic motility and defecation by RS-127445 suggests an involvement of the 5-HT2B receptor in rodent large bowel physiology

BACKGROUND

5-HT(2B) receptors are localized within the myenteric nervous system, but their functions on motor/sensory neurons are unclear. To explore the role of these receptors, we further characterized the 5-HT(2B) receptor antagonist RS-127445 and studied its effects on peristalsis and defecation.

EXPERIMENTAL APPROACH

Although reported as a selective 5-HT(2B) receptor antagonist, any interactions of RS-127445 with 5-HT(4) receptors are unknown; this was examined using the recombinant receptor and Biomolecular Interaction Detection technology. Mouse isolated colon was mounted in tissue baths for isometric recording of neuronal contractions evoked by electrical field stimulation (EFS), or under an intraluminal pressure gradient to induce peristalsis; the effects of RS-127445 on EFS-induced and on peristaltic contractions were measured. Faecal output of rats in grid-bottom cages was measured over 3 h following i.p. RS-127445 and separately, validation of the effective doses was achieved by determining the free, unbound fraction of RS-127445 in blood and brain.

KEY RESULTS

RS-127445 (up to 1 micromol x L(-1)) did not interact with the 5-HT(4) receptor. RS-127445 (0.001-1 micromol x L(-1)) did not affect EFS-induced contractions of the colon, although at 10 micromol x L(-1) the contractions were reduced (to 36 +/- 8% of control, n= 4). RS-127445 (0.1-10 micromol x L(-1)) concentration-dependently reduced peristaltic frequency (n= 4). RS-127445 (1-30 mg x kg(-1)), dose-dependently reduced faecal output, reaching significance at 10 and 30 mg x kg(-1) (n= 6-11). In blood and brain, >98% of RS-127445 was protein-bound.

CONCLUSIONS AND IMPLICATIONS

High-protein binding of RS-127445 indicates that relatively high doses are required for efficacy. The results suggest that 5-HT(2B) receptors tonically regulate colonic motility.

Direct subunit-dependent multimodal 5-hydroxytryptamine3 receptor antagonism by methadone

Homomeric 5-hydroxytryptamine (5-HT)(3A) and heteromeric 5-HT(3AB) receptors mediate rapid excitatory responses to serotonin in the central and peripheral nervous systems. The alkaloid morphine, in addition to being a mu-opioid receptor agonist, is a potent competitive inhibitor of 5-HT(3) receptors. We examined whether methadone, an opioid often used to treat morphine dependence, also exhibited 5-HT(3) receptor antagonist properties. Racemic (R/S)-methadone inhibited currents mediated by human homomeric 5-HT(3A) receptors (IC(50) = 14.1 +/- 2.5 microM). Incorporation of the 5-HT(3B) subunit into heteromeric 5-HT(3AB) receptors reduced the potency of inhibition by (R/S)-methadone (IC(50) = 41.1 +/- 0.9 microM). (R/S)-Methadone also increased apparent desensitization of both 5-HT(3) receptor subtypes. The inhibition of the 5-HT(3A) receptor was competitive; however, incorporation of the 5-HT(3B) subunit caused the appearance of inhibition that was insurmountable by 5-HT. In the absence of rapid desensitization, when dopamine was used as an agonist of 5-HT(3AB) receptors, the inhibition by (R/S)-methadone was voltage-dependent. The antagonist and desensitization-enhancing effects of (R/S)-methadone were shared by pure (R)- and (S)-methadone enantiomers, which had similar actions on 5-HT-evoked currents mediated by 5-HT(3) receptors. However, (R)-methadone exhibited a larger voltage-dependent inhibition of dopamine-evoked currents mediated by 5-HT(3AB) receptors than did (S)-methadone. Inhibition of 5-HT(3A) receptors by (R/S)-methadone was not influenced by voltage. Thus, methadone displays multimodal subunit-dependent antagonism of 5-HT(3) receptors.

Identification of patients with non-d, non-C irritable bowel syndrome and treatment with renzapride: an exploratory, multicenter, randomized, double-blind, placebo-controlled clinical trial

This was an exploratory study of renzapride in 168 male and female patients with non-D, non-C irritable bowel syndrome (IBS). Patients were randomized to placebo or renzapride (1, 2, or 4 mg/day) for 8 weeks. The primary efficacy variable was patient-reported satisfactory relief of IBS symptoms. Secondary variables included relief of abdominal pain/discomfort. The proportion of patients reporting satisfactory relief of their IBS symptoms for at least 50% of the time did not differ significantly from those on placebo. However, post hoc analysis in women showed differences in responder rate on renzapride versus placebo of 18.2% (95% CI -5% to 42%; P = 0.066) during weeks 1-4 and 6% (95% CI -21% to 33%; P = 0.339) during weeks 5-8. Renzapride was well tolerated and most adverse events were mild to moderate in intensity. Further studies are warranted to determine whether renzapride is beneficial in this patient population.

Serotonin and GI clinical disorders

Serotonin is widely distributed throughout the gut within both the enteric nerves and enterochromaffin (EC) cells. EC cells are located in the gut mucosa with maximal numbers in the duodenum and rectum where they act as signal transducers, responding to pressure and luminal substances both bacterial and dietary. Activation leads to serotonin release which acts on a range of receptors on mucosal afferent and myenteric interneurones to initiate secretomotor reflexes. These cause nausea and vomiting as well as intestinal secretion, propulsion and if pronounced, diarrhoea. Inflammation in animal models acts via T lymphocytes to increase EC cell numbers and mucosal serotonin (5-HT) content while inflammatory cytokines decrease serotonin transporter (SERT) function. Inflammation due to coeliac disease and following gastrointestinal infection increases mucosal 5-HT availability by a combination of increased EC cells and depressed SERT. Irritable bowel syndrome (IBS) developing after gastrointestinal infection and IBS with diarrhoea is associated with excess 5-HT. The associated diarrhoeal symptoms respond well to 5-HT(3) receptor antagonists. These drugs also inhibit the nausea and vomiting occurring in patients undergoing chemotherapy which cause a marked increase in release of 5-HT as well as other mediators. Other conditions including IBS-C and constipation may have inadequate 5-HT release and benefit from both 5-HT(3) and 5-HT(4) receptor agonists.

Mechanisms of serotonergic agents for treatment of gastrointestinal motility and functional bowel disorders

Most of the body's serotonin is released in the gut where it plays an important role in the control of gastrointestinal (GI) motility, sensitivity and muscle tone by activating different receptor subtypes. This review focuses on the known effects of selective serotonin reuptake inhibitor and serotonin receptor agonists and antagonists on the sensorimotor function of the GI tract and describes the therapeutic potential of these actions for GI motility and functional bowel disorders.

Increased presence of serotonin-producing cells in colons with diverticular disease may indicate involvement in the pathophysiology of the condition

INTRODUCTION

Serotonin is an important neuroendocrine transmitter participating in the control of colonic motor activity through neural and biochemical mechanisms in the Enteric Nervous System (ENS). A possible pathophysiological factor for diverticular disease (DD) is altered colonic motility. The study compared the distribution of serotonin cells (SC) in the colonic mucosa of patients with diverticular disease to controls.

METHODS

Sixteen paraffin specimens with sigmoid diverticular disease were selected and sections of bowel without diverticula from the same specimen were used as its own control. The resection margins from sixteen colonic specimens excised for sigmoid cancer were additional controls. Immunocytochemical staining for serotonin cells was performed on 4-mum tissue sections with polyclonal antibody (NCL-SEROTp). The number of serotonin-positive cells per ten microscopic fields (x200) was assessed in all groups and the staining distribution was defined as low (0-33%), moderate (>33-66%) and high (>66%) according to the percentage of the entire cell containing contrast material. The control specimens were blinded before analysis. Student's t test was used for statistical analysis and significance level was set as P < 0.05.

RESULTS

The mean number of serotonin-positive cells per ten fields in the colonic mucosa of specimens with diverticular disease was significantly higher [252.44 (SD 90.64)] than the specimen's own control [147.31 (SD 50.16)] and at normal resection margins of cancer specimens [228.38 (SD 120.10)]. The paired analysis between diverticular disease specimens and its own control (paired t test) showed significant differences for moderate (P = 0.008), high (P = 0.001) and total (P = 0.002) number of serotonin cells. There was no evidence of significance between mean DD and cancer values.

DISCUSSION

Increased presence of SCs and the higher proportion of high and moderate staining cells (indicating increased hormone content) indicate the possible role of serotonin in DD. This may be contributing to the pathogenesis of the condition by altered colonic motility in the affected segments in a similar way as in irritable bowel syndrome.

Pharmacological Properties of 3-Amino-5,6,7,8-tetrahydro-2-{4-[4-(quinolin-2-yl)piperazin-1-yl]butyl}quinazolin-4(3H)-one (TZB-30878), a Novel Therapeutic Agent for Diarrhea-Predominant Irritable Bowel Syndrome (IBS) and Its Effects on an Experimental IBS Model

3-Amino-5,6,7,8-tetrahydro-2-[4-[4-(quinolin-2-yl)piperazin-1-yl]butyl]quinazolin-4(3H)-one (TZB-30878) is a novel compound with both 5-hydroxytryptamine (5-HT)(1A) agonism and 5-HT(3) antagonism effects. We hypothesized that TZB-30878 might have benefits from these dual effects as a medication for diarrhea-predominant irritable bowel syndrome (d-IBS), and these studies were designed to confirm the pharmacological properties of TZB-30878 and its efficacy in an IBS-like animal model. The binding assays demonstrated that [(3)H]TZB-30878 selectively binds to human 5-HT(1A) and 5-HT(3) receptors, with K(d) values of 0.68 +/- 0.03 and 8.90 +/- 1.73 nM, respectively. Systemic administration of TZB-30878 inhibited 5-HT-induced bradycardia in a dose-dependent manner in rats. In behavioral assays TZB-30878 produced signs of 5-HT syndrome in rats. These results suggest that TZB-30878 has dual effects as a 5-HT(1A) receptor agonist and a 5-HT(3) receptor antagonist. Finally, we evaluated the effects of TZB-30878 on wrap restraint stress-induced defecation in an IBS-like model in rats. TZB-30878 (1-10 mg/kg p.o.) normalized stress-induced defecation in a dose-dependent manner, whereas the 5-HT(1A) agonist tandospirone (30 and 100 mg/kg p.o.) and the 5-HT(3) antagonist alosetron (1-10 mg/kg p.o.) did not show such effects. Furthermore, this efficacy of TZB-30878 was partly antagonized by a 5-HT(1A) antagonist, [O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY-100635). These results suggest that 5-HT(1A) receptor agonism and 5-HT(3) receptor antagonism contribute to the efficacy of TZB-30878 in the IBS-like model. The efficacy of TZB-30878 supports the concept that the presence of both actions, namely 5-HT(1A) receptor agonism and 5-HT(3) receptor antagonism, could be an important mechanism in the treatment of d-IBS.

Postoperative colonic motility after tropisetron and a standardized meal in patients undergoing conventional colorectal surgery

BACKGROUND

Early postoperative enteral nutrition is advantageous for the recovery of colonic motility but may be limited by abdominal distension, nausea, and vomiting. We aimed to investigate the tolerance of a standardized meal after pretreatment with the 5-hydroxytryptamine-3-receptor antagonist tropisetron and to study the concomitant colonic motility.

METHODS

Colonic motility and tone were recorded on postoperative day 1 to 3 with a combined manometry/barostat recording catheter in 12 patients who underwent open colorectal surgery with an anastomosis in the distal colon or rectum. The study protocol consisted of 30 min of baseline recordings followed by 5 mg of tropisetron intravenously. Then, motility was recorded for another 30 min before patients ingested a standardized meal to trigger the gastrocolonic response. Postprandial motility was recorded for the subsequent 60 min.

RESULTS

The colonic motility index increased after administration of tropisetron on all three postoperative days (day 1: 34+/-11 vs 122+/-48, day 2: 55+/-19 vs 101+/-25, and day 3: 42+/-16 vs 93+/-33 mmHg/min; p<0.05). No further increase of the motility index was observed postprandially. Frequency and amplitude of contractions were virtually unaffected by tropisetron and the meal. Barostat bag volume decreased postprandially in the proximal bag on the third, and in the distal bag on the first and second postoperative day (p<0.05). Patients' condition was unaffected by the standardized meal after tropisetron administration.

CONCLUSIONS

Tropisetron may enhance colonic motility in the early postoperative period; however, the gastrocolonic response was impaired thereafter. High caloric food intake is well tolerated early after surgery after tropisetron pretreatment.

Serotonin and its role in colonic function and in gastrointestinal disorders

Serotonin (5-HT) is most commonly thought of as a neurotransmitter in the central nervous system. However, the predominant site of serotonin synthesis, storage, and release is the enterochromaffin cells of the intestinal mucosa. Within the intestinal mucosa, serotonin released from EC cells activates neural reflexes associated with intestinal secretion, motility, and sensation. Two important receptors for serotonin that are located in the neural circuitry of the intestines are the 5-HT(3) and 5-HT(4) receptors; these are the targets of drugs designed to treat gastrointestinal disorders. 5-HT(3) receptor antagonists are used to treat nausea and emesis associated with chemotherapy and for functional disorders associated with diarrhea. 5-HT(4) receptor agonists are used as promotility agents to promote gastric emptying and to alleviate constipation. Because of the importance of serotonin in normal gut function and sensation, a number of studies have investigated potential changes in mucosal serotonin signaling in pathologic conditions. Despite the inconsistencies in the current literature, changes in serotonin signaling have now been demonstrated in inflammatory bowel disease, irritable bowel syndrome, postinfectious irritable bowel syndrome, and idiopathic constipation. Emerging evidence has led to many contradictory theories regarding serotonin signaling and its roles in the pathology of gut disorders. This review summarizes the current medications affecting serotonin signaling and provides an overview of our current knowledge of the changes in serotonin that occur in pathologic conditions.

Reliability of the ICRP'S dose coefficients for members of the public: IV. basis of the human alimentary tract model and uncertainties in model predictions

The biokinetic and dosimetric model of the gastrointestinal (GI) tract applied in current documents of the International Commission on Radiological Protection (ICRP) was developed in the mid-1960s. The model was based on features of a reference adult male and was first used by the ICRP in Publication 30, Limits for Intakes of Radionuclides by Workers (Part 1, 1979). In the late 1990s an ICRP task group was appointed to develop a biokinetic and dosimetric model of the alimentary tract that reflects updated information and addresses current needs in radiation protection. The new age-specific and gender-specific model, called the Human Alimentary Tract Model (HATM), has been completed and will replace the GI model of Publication 30 in upcoming ICRP documents. This paper discusses the basis for the structure and parameter values of the HATM, summarises the uncertainties associated with selected features and types of predictions of the HATM and examines the sensitivity of dose estimates to these uncertainties for selected radionuclides. Emphasis is on generic biokinetic features of the HATM, particularly transit times through the lumen of the alimentary tract, but key dosimetric features of the model are outlined, and the sensitivity of tissue dose estimates to uncertainties in dosimetric as well as biokinetic features of the HATM are examined for selected radionuclides.

The serotonin signaling system: from basic understanding to drug development for functional GI disorders

Serotonin is an important gastrointestinal signaling molecule. It is a paracrine messenger utilized by enterochromaffin (EC) cells, which function as sensory transducers. Serotonin activates intrinsic and extrinsic primary afferent neurons to, respectively, initiate peristaltic and secretory reflexes and to transmit information to the central nervous system. Serotonin is also a neurotransmitter utilized by a system of long descending myenteric interneurons. Serotonin is synthesized through the actions of 2 different tryptophan hydroxylases, TpH1 and TpH2, which are found, respectively, in EC cells and neurons. Serotonin is inactivated by the serotonin reuptake transporter (SERT)-mediated uptake into enterocytes or neurons. The presence of many serotonin receptor subtypes enables selective drugs to be designed to therapeutically modulate gastrointestinal motility, secretion, and sensation. Current examples include tegaserod, a 5-HT(4) partial agonist, which has been approved for treatment of irritable bowel syndrome (IBS) with constipation in women and for chronic constipation in men and women. The 5-HT(3) antagonists, granisetron and ondansetron, are useful in combating the nausea associated with cancer chemotherapy, and alosetron is employed in the treatment of IBS with diarrhea. Serotonergic signaling abnormalities have also been putatively implicated in the pathogenesis of functional bowel diseases. Other compounds, for which efficacy has not been rigorously established, but which may have value, include tricyclic antidepressants and serotonin selective reuptake inhibitors to combat IBS, and 5-HT(1) agonists, which enhance gastric accommodation, to treat functional dyspepsia. The initial success encountered with serotonergic agents holds promise for newer and more potent insights and therapies of brain-gut disorders.