Cannabinoid receptor agonism inhibits transient lower esophageal sphincter relaxations and reflux in dogs

Should gastroenterologists prescribe cannabis? The highs, the lows and the unknowns

Cannabis, commonly known as marijuana, is a drug extracted from the Cannabis plant known for its psychotropic and medicinal properties. It has been used for healing purposes during ancient times, although its psychoactive components led to its restricted use in medicine. Nonetheless, cannabis is found to have modulatory effects on the endocannabinoid system exhibiting its medicinal role in the gastrointestinal (GI) system. Emerging animal and human studies demonstrate the influential effects of cannabis on a variety of GI diseases including inflammatory bowel disease, motility disorders and GI malignancies. It also has a regulatory role in GI symptoms including nausea and vomiting, anorexia, weight gain, abdominal pain, among others. However, both its acute and chronic use can lead to undesirable side effects such as dependency and addiction, cognitive impairment and cannabinoid hyperemesis syndrome. We will discuss the role of cannabis in the GI system as well as dosing strategies to help guide gastroenterologists to assess its efficacy and provide patient counseling before prescription of medical marijuana.

Gastroparesis with Cannabis Use: A Retrospective Study from the Nationwide Inpatient Sample

Background: With increasing utilization of cannabis in the United States (US), clinicians may encounter more cases of Gastroparesis (GP) in coming years.Objective: The primary outcome was inpatient mortality for GP with cannabis use. Secondary outcomes included system-based complications and the burden of the disease on the US healthcare system.Methods: From the Nationwide Inpatient Sample (NIS), we identified adult hospitalizations with a primary discharge diagnosis of GP for 2016 and 2017. Individuals ≤18 years of age were excluded. The study population was subdivided based on a secondary diagnosis of cannabis use. The outcomes included biodemographic characteristics, mortality, complications, and burden of disease on the US healthcare system.Results: For 2016 and 2017, we identified 99,695 hospitalizations with GP. Of these hospitalizations, 8,870 had a secondary diagnosis of cannabis use while 90,825 served as controls. The prevalence of GP with cannabis use was 8.9%. For GP with cannabis use, the patients were younger (38.5 vs 48.1 years, p < 0.001) with a Black predominance (Table 1) and lower proportion of females (52.3 vs 68.3%, p < 0.001) compared to the non-cannabis use cohort. Additionally, the cannabis use cohort had higher percentage of patients with co-morbidities like hypertension, diabetes mellitus and a history of smoking. The inpatient mortality for GP with cannabis use was noted to be 0.27%. Furthermore, we noted shorter mean length of stay (LOS) (3.4 vs 4.4 days, aMD: -0.7, 95%CI: -0.9 - [-0.5], p < 0.001), lower mean total hospital charge (THC) ($30,400 vs $38,100, aMD: -5100, 95%CI: -6900 - [-3200], p < 0.001), and lower rates of sepsis (0.11 vs 0.60%, aOR: 0.22, 95% CI: 0.05-0.91, p = 0.036) for GP hospitalizations with cannabis use compared to the non-cannabis use cohort.Conclusion: Inpatient mortality for GP hospitalizations with cannabis use was 0.27%. Additionally, these patients had shorter LOS, lower THC, and lower sepsis rates.

Cannabinoid pharmacology and therapy in gut disorders

Cannabis sp. and their products (marijuana, hashish…), in addition to their recreational, industrial and other uses, have a long history for their use as a remedy for symptoms related with gastrointestinal diseases. After many reports suggesting these beneficial effects, it was not surprising to discover that the gastrointestinal tract expresses endogenous cannabinoids, their receptors, and enzymes for their synthesis and degradation, comprising the so-called endocannabinoid system. This system participates in the control of tissue homeostasis and important intestinal functions like motor and sensory activity, nausea, emesis, the maintenance of the epithelial barrier integrity, and the correct cellular microenvironment. Thus, different cannabinoid-related pharmacological agents may be useful to treat the main digestive pathologies. To name a few examples, in irritable bowel syndrome they may normalize dysmotility and reduce pain, in inflammatory bowel disease they may decrease inflammation, and in colorectal cancer, apart from alleviating some symptoms, they may play a role in the regulation of the cell niche. This review summarizes the main recent findings on the role of cannabinoid receptors, their synthetic or natural ligands and their metabolizing enzymes in normal gastrointestinal function and in disorders including irritable bowel syndrome, inflammatory bowel disease, colon cancer and gastrointestinal chemotherapy-induced adverse effects (nausea/vomiting, constipation, diarrhea).

Pathophysiological Mechanisms of Gastrointestinal Toxicity

Humans swallow a great variety and often large amounts of chemicals as nutrients, incidental food additives and contaminants, drugs, and inhaled particles and chemicals, thus exposing the gastrointestinal tract to many potentially toxic substances. It serves as a barrier in many cases to protect other components of the body from such substances and infections. Fortunately, the gastrointestinal tract is remarkably robust and generally is able to withstand multiple daily assaults by the chemicals to which it is exposed. Some chemicals, however, can affect one or more aspects of the gastrointestinal tract to produce abnormal events that reflect toxicity. It is the purpose of this chapter to evaluate the mechanisms by which toxic chemicals produce their deleterious effects and to determine the consequences of the toxicity on integrity of gastrointestinal structure and function. Probably because of the intrinsic ability of the gastrointestinal tract to resist toxic chemicals, there is a paucity of data regarding gastrointestinal toxicology. It is therefore necessary in many cases to extrapolate toxic mechanisms from infectious processes, inflammatory conditions, ischemia, and other insults in addition to more conventional chemical sources of toxicity.

Review: The Role of Cannabinoids on Esophageal Function-What We Know Thus Far

The endocannabinoid system (ECS) primarily consists of cannabinoid receptors (CBRs), endogenous ligands, and enzymes for endocannabinoid biosynthesis and inactivation. Although the presence of CBRs, both CB1 and CB2, as well as a third receptor (G-protein receptor 55 [GPR55]), has been established in the gastrointestinal (GI) tract, few studies have focused on the role of cannabinoids on esophageal function. To date, studies have shown their effect on GI motility, inflammation and immunity, intestinal and gastric acid secretion, nociception and emesis pathways, and appetite control. Given the varying and sometimes limited efficacy of current medical therapies for diseases of the esophagus, further understanding and investigation into the interplay of the ECS on esophageal health and disease may present new therapeutic modalities that may help advance current treatment options. In this brief review, the current understanding of the ECS role in various esophageal functions and disorders is presented.

Complementary Therapies in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) often take a chronic debilitating course. Given the chronicity of IBD, the limitations of the available medications, their potential side effects, and the impact of the disease on patients' quality of life, it is not surprising IBD patients are ranked among the highest users of complementary and alternative medicine (CAM). Since CAM has become very popular in real-life practice of Western Communities, caregivers must gain more knowledge about these therapies, their mechanism of action, benefits, and risks. This article reviews and discusses up-to-date scientific and clinical data regarding the most prevalent herbal CAM therapies.

Cannabinoids and GI Disorders: Endogenous and Exogenous

OPINION STATEMENT

Despite the political and social controversy affiliated with it, the medical community must come to the realization that cannabinoids exist as a ubiquitous signaling system in many organ systems. Our understanding of cannabinoids and how they relate not only to homeostasis but also in disease states must be furthered through research, both clinically and in the laboratory. The identification of the cannabinoid receptors in the early 1990s have provided us with the perfect target of translational research. Already, much has been done with cannabinoids and the nervous system. Here, we explore the implications it has for the gastrointestinal tract. Most therapeutics currently on the market presently target only one aspect of the cannabinoid system. Our main purpose here is to highlight areas of research and potential avenues of discovery that the cannabinoid system has yet to reveal.

Cannabinoid Receptors in Regulating the GI Tract: Experimental Evidence and Therapeutic Relevance

Cannabinoid receptors are fundamentally involved in all aspects of intestinal physiology, such as motility, secretion, and epithelial barrier function. They are part of a broader entity, the so-called endocannabinoid system which also includes their endocannabinoid ligands and the ligands' synthesizing/degrading enzymes. The system has a strong impact on the pathophysiology of the gastrointestinal tract and is believed to maintain homeostasis in the gut by controlling hypercontractility and by promoting regeneration after injury. For instance, genetic knockout of cannabinoid receptor 1 leads to inflammation and cancer of the intestines. Derivatives of Δ⁹-tetrahydrocannabinol, such as nabilone and dronabinol, activate cannabinoid receptors and have been introduced into the clinic to treat chemotherapy-induced emesis and loss of appetite; however, they may cause many psychotropic side effects. New drugs that interfere with endocannabinoid degradation to raise endocannabinoid levels circumvent this obstacle and could be used in the future to treat emesis, intestinal inflammation, and functional disorders associated with visceral hyperalgesia.

The Physiology of Eructation

Eructation is composed of three independent phases: gas escape, upper barrier elimination, and gas transport phases. The gas escape phase is the gastro-LES inhibitory reflex that causes transient relaxation of the lower esophageal sphincter, which is activated by distension of stretch receptors of the proximal stomach. The upper barrier elimination phase is the transient relaxation of the upper esophageal sphincter along with airway protection. This phase is activated by stimulation of rapidly adapting mechanoreceptors of the esophageal mucosa. The gas transport phase is esophageal reverse peristalsis mediated by elementary reflexes, and it is theorized that this phase is activated by serosal rapidly adapting tension receptors. Alteration of the receptors which activate the upper barrier elimination phase of eructation by gastro-esophageal reflux of acid may in part contribute to the development of supra-esophageal reflux disease.

Changes in Gene Expression Patterns of Circadian-Clock, Transient Receptor Potential Vanilloid-1 and Nerve Growth Factor in Inflamed Human Esophagus

Circadian rhythm is driven by the molecular circadian-clock system and regulates many physiological functions. Diurnal rhythms in the gastrointestinal tract are known to be related to feeding pattern, but whether these rhythms are also related to the gastrointestinal damage or injuries; for example, gastroesophageal reflux disease (GERD), is unclear. This study was conducted to determine whether expression of circadian-clock genes or factors involved in vagal stimulation or sensitization were altered in the esophagus of GERD patients. Diurnal patterns of PER1, PER2, BMAL1, CRY2, TRPV1, and NGF mRNA expression were found in patient controls, and these patterns were altered and significantly correlated to the GERD severity in GERD patients. Although levels of CRY1, TIM, CB1, NHE3, GDNF, and TAC1 mRNA expression did not show diurnal patterns, they were elevated and also correlated with GERD severity in GERD patients. Finally, strong correlations among PER1, TRPV1, NGF and CRY2 mRNA expression, and among PER2, TRPV1 and CRY2 expression were found. Expression levels of CRY1 mRNA highly correlated with levels of TIM, CB1, NHE3, GDNF and TAC1. This study suggests that the circadian rhythm in the esophagus may be important for the mediation of and/or the response to erosive damage in GERD patients.

Endocannabinoid signaling at the periphery: 50 years after THC

In 1964, the psychoactive ingredient of Cannabis sativa, Δ(9)-tetrahydrocannabinol (THC), was isolated. Nearly 30 years later the endogenous counterparts of THC, collectively termed endocannabinoids (eCBs), were discovered: N-arachidonoylethanolamine (anandamide) (AEA) in 1992 and 2-arachidonoylglycerol (2-AG) in 1995. Since then, considerable research has shed light on the impact of eCBs on human health and disease, identifying an ensemble of proteins that bind, synthesize, and degrade them and that together form the eCB system (ECS). eCBs control basic biological processes including cell choice between survival and death and progenitor/stem cell proliferation and differentiation. Unsurprisingly, in the past two decades eCBs have been recognized as key mediators of several aspects of human pathophysiology and thus have emerged to be among the most widespread and versatile signaling molecules ever discovered. Here some of the pioneers of this research field review the state of the art of critical eCB functions in peripheral organs. Our community effort is aimed at establishing consensus views on the relevance of the peripheral ECS for human health and disease pathogenesis, as well as highlighting emerging challenges and therapeutic hopes.

New and future drug development for gastroesophageal reflux disease

Medical therapy remains the most popular treatment for gastroesophageal reflux disease (GERD). Whilst interest in drug development for GERD has declined over the last few years primarily due to the conversion of most proton pump inhibitor (PPI)'s to generic and over the counter compounds, there are still numerous areas of unmet needs in GERD. Drug development has been focused on potent histamine type 2 receptor antagonist's, extended release PPI's, PPI combination, potassium-competitive acid blockers, transient lower esophageal sphincter relaxation reducers, prokinetics, mucosal protectants and esophageal pain modulators. It is likely that the aforementioned compounds will be niched for specific areas of unmet need in GERD, rather than compete with the presently available anti-reflux therapies.

The relevance of transient lower oesophageal sphincter relaxations in the pathophysiology and treatment of GORD

Gastro-oesophageal reflux disease (GORD) is associated with the passage of gastric contents into the oesophagus resulting in potential oesophageal damage and impaired quality of life. GORD is a frequently encountered problem in today's population, with 25% of people in western populations reporting such symptoms at least once a month. Proton pump inhibitors (PPI) are the drug of choice, with surgery being employed in refractory cases. Although acid suppression is often effective, some patients remain symptomatic despite maximal PPI therapy. By delving into the mechanisms of the disease, it is clear that transient lower oesophageal sphincter relaxations are a key component of its pathophysiology. Research has demonstrated various therapeutic targets for reducing the frequency of such relaxations through GABA and glutamate modulation, for instance. This review highlights such modulations and hopes to explore these mechanisms and therapeutic targets in an area that will no doubt see a change in its pharmacological management in the near future.

Cannabinoids facilitate the swallowing reflex elicited by the superior laryngeal nerve stimulation in rats

Cannabinoids have been reported to be involved in affecting various biological functions through binding with cannabinoid receptors type 1 (CB1) and 2 (CB2). The present study was designed to investigate whether swallowing, an essential component of feeding behavior, is modulated after the administration of cannabinoid. The swallowing reflex evoked by the repetitive electrical stimulation of the superior laryngeal nerve in rats was recorded before and after the administration of the cannabinoid receptor agonist, WIN 55-212-2 (WIN), with or without CB1 or CB2 antagonist. The onset latency of the first swallow and the time intervals between swallows were analyzed. The onset latency and the intervals between swallows were shorter after the intravenous administration of WIN, and the strength of effect of WIN was dose-dependent. Although the intravenous administration of CB1 antagonist prior to intravenous administration of WIN blocked the effect of WIN, the administration of CB2 antagonist did not block the effect of WIN. The microinjection of the CB1 receptor antagonist directly into the nucleus tractus solitarius (NTS) prior to intravenous administration of WIN also blocked the effect of WIN. Immunofluorescence histochemistry was conducted to assess the co-localization of CB1 receptor immunoreactivity to glutamic acid decarboxylase 67 (GAD67) or glutamate in the NTS. CB1 receptor was co-localized more with GAD67 than glutamate in the NTS. These findings suggest that cannabinoids facilitate the swallowing reflex via CB1 receptors. Cannabinoids may attenuate the tonic inhibitory effect of GABA (gamma-aminobuteric acid) neurons in the central pattern generator for swallowing.

Targeting the endocannabinoid system for gastrointestinal diseases: future therapeutic strategies

Cannabinoids extracted from the marijuana plant (Cannabis sativa) and synthetic cannabinoids have numerous effects on gastrointestinal (GI) functions. Recent experimental data support an important role for cannabinoids in GI diseases. Genetic studies in humans have proven that defects in endocannabinoid metabolism underlie functional GI disorders. Mammalian cells have machinery, the so-called endocannabinoid system (ECS), to produce and metabolize their own cannabinoids in order to control homeostasis of the gut in a rapidly adapting manner. Pharmacological manipulation of the ECS by cannabinoids, or by drugs that raise the levels of endogenous cannabinoids, have shown beneficial effects on GI pathophysiology. This review gives an introduction into the functions of the ECS in the GI tract, highlights the role of the ECS in GI diseases and addresses its potential pharmacological exploitation.

Gastroesophageal reflux disease--from reflux episodes to mucosal inflammation

Gastroesophageal reflux disease (GERD) affects 20-30% of the population in Western countries, and is one of the most common clinical problems in daily practice. GERD-associated functional and structural abnormalities are caused by recurrent exposure of the esophagus to acidic and nonacidic refluxate of gastric contents (containing duodenal and intestinal proteases as well as acid and gastric pepsin) from the stomach. Major progress has been made in the understanding of the molecular pathogenesis of GERD-associated mucosal inflammation, suggesting a complex and multifactorial pathogenesis and immune-mediated effects. This Review summarizes the complexity of mucosal pathogenesis, including microscopic changes, mucosal inflammation and GERD-specific molecular mediators, in the context of the clinical features and pathophysiological characteristics of GERD. The abnormal exposure of the esophagus to luminal contents leads to chronic mucosal inflammation that is characterized by the release of IL-8 specifically, as well as other proinflammatory mediators, from the esophageal mucosa. Evidence from animal studies indicates a stepwise inflammatory response by the epithelium, which attracts immune effector cells to infiltrate the mucosa. From bench to bedside, these novel molecular findings might provide new treatment options beyond current acid-suppressive therapy and the principle of inhibition of transient lower esophageal sphincter relaxation.

New pharmacologic approaches in gastroesophageal reflux disease

This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.

Alternative targets within the endocannabinoid system for future treatment of gastrointestinal diseases

Many beneficial effects of herbal and synthetic cannabinoids on gut motility and inflammation have been demonstrated, suggesting a vast potential for these compounds in the treatment of gastrointestinal disorders. These effects are based on the so-called 'endocannabinoid system' (ECS), a cooperating network of molecules that regulate the metabolism of the body's own and of exogenously administered cannabinoids. The ECS in the gastrointestinal tract quickly responds to homeostatic disturbances by de novo synthesis of its components to maintain homeostasis, thereby offering many potential targets for pharmacological intervention. Of major therapeutic interest are nonpsychoactive cannabinoids or compounds that do not directly target cannabinoid receptors but still possess cannabinoid-like properties. Drugs that inhibit endocannabinoid degradation and raise the level of endocannabinoids are becoming increasingly promising alternative therapeutic tools to manipulate the ECS.

Who are medical marijuana patients? Population characteristics from nine California assessment clinics

Marijuana is a currently illegal psychoactive drug that many physicians believe has substantial therapeutic uses. The medical literature contains a growing number of studies on cannabinoids as well as case studies and anecdotal reports suggesting therapeutic potential. Fifteen states have passed medical marijuana laws, but little is known about the growing population of patients who use marijuana medicinally. This article reports on a sample of 1,746 patients from a network of nine medical marijuana evaluation clinics in California. Patients completed a standardized medical history form; evaluating physicians completed standardized evaluation forms. From this data we describe patient characteristics, self-reported presenting symptoms, physician evaluations, other treatments tried, other drug use, and medical marijuana use practices. Pain, insomnia, and anxiety were the most common conditions for which evaluating physicians recommended medical marijuana. Shifts in the medical marijuana patient population over time, the need for further research, and the issue of diversion are discussed.

Advances in drug therapy for gastroesophageal reflux disease

The incidence of gastroesophageal reflux disease (GERD) is increasing drastically in China. GERD could probably cause reflux esophagitis, chronic cough, asthma, Barrett's esophagus and adenocarcinoma, and frequently affects health-related quality of life. The use of proton pump inhibitors (PPIs) provides effective symptomatic relief in most patients; however, some patients appear refractory to the treatment with PPIs. The long term use of PPIs might also cause adverse effects, such as interstitial nephritis, fracture and small intestinal bacterial overgrowth. Many new drugs for GERD have emerged recently. This article reviews the advances in drug therapy for GERD.

Review article: the clinical relevance of transient lower oesophageal sphincter relaxations in gastro-oesophageal reflux disease

BACKGROUND

Transient lower oesophageal sphincter relaxations (TLOSR) are considered the physiological mechanism that enables venting of gas from the stomach and appear as sphincter relaxations that are not induced by swallowing. It has become increasingly clear that most reflux episodes occur during TLOSRs and therefore play a key role in gastro-oesophageal reflux disease (GERD).

AIM

To describe the current knowledge about TLOSRs and its clinical implications.

METHODS

Search of the literature published in English using the PubMed database and relevant abstracts presented at international conventions.

RESULTS

Several factors influence the rate of TLOSRs including anti-reflux surgery, meal, body position, nutrition, lifestyle and a wide array of neurotransmitters. Ongoing insights in the neurotransmitters responsible for the modulation of TLOSRs, as well as the neural pathways involved in TLOSR induction, have lead to novel therapeutic targets. These therapeutic targets can serve as an add-on therapy in patients with an unsatisfactory response to proton pump inhibitor by inhibiting TLOSRs and its associated reflux events. However, the TLOSR-inhibiting drugs that are currently available still have significant side effects.

CONCLUSION

It is likely that in the future, selected GERD patients may benefit from transient lower oesophageal sphincter relaxation inhibition when compounds are found without significant side effects.

Effect of rimonabant on oesophageal motor function in man

BACKGROUND

Cannabinoid type 1 (CB1) receptors are implicated in the control of transient lower oesophageal sphincter relaxations (TLESRs) in animals. In man, it is unclear whether CB1 receptors are involved in the control of oesophageal function.

AIM

To study the effects of the CB1 receptor antagonist rimonabant on fasting and postprandial LES function in healthy subjects.

METHODS

Twelve healthy volunteers underwent two oesophageal manometry studies with administration of wet swallows and a meal after 3 days' premedication with placebo or rimonabant 20 mg.

RESULTS

Rimonabant did not significantly alter preprandial LES pressure (21.1±4.0 vs. 17.3±3.0 mmHg, N.S.), but postprandial LES pressures were significantly enhanced (9.9±1.9 vs.17.1±2.7 mmHg in the first and 10.0±1.4 vs. 19.3±3.6 mmHg in the second postprandial hour, both P<0.05). Swallow-induced relaxations and amplitude of peristaltic contractions were not altered, but rimonabant significantly increased the duration of peristaltic contractions at all time points (e.g. 5.0±0.3 vs. 8.0±0.3s preprandially and 5.0±0.2 vs. 8.2±0.3s at 60 min postprandially, both P<0.01). The number of postprandial TLESRs (3.1±0.5 vs. 1.2±0.5, P<0.05) and acid reflux episodes (1.4±0.2 vs. 0.3±0.1, P<0.05) were significantly lower after rimonabant.

CONCLUSION

The CB1 receptor antagonist rimonabant enhances postprandial LES pressure and decreases TLESRs in healthy subjects.

Beyond acid suppression: new pharmacologic approaches for treatment of GERD

Proton pump inhibitors are highly successful in treating gastroesophageal reflux disease, but a significant proportion of patients have persistent symptoms from weakly or nonacidic reflux. Transient lower esophageal sphincter relaxation (TLESR) represents the dominant mechanism of gastroesophageal reflux and has therefore become the most intensely investigated therapeutic target. The triggering of TLESR involve the vagal pathways and the gamma-aminobutyric type B (GABA(B)) and metabotropic glutamate type 5 (mGluR5) receptors. Baclofen is a GABA(B) receptor agonist that is effective in inhibiting TLESR and reducing the number of reflux episodes, but is associated with significant central nervous system (CNS) side effects. The newer GABA(B) agonists, such as AZD9343 and AZD3355, and mGluR5 antagonists, such as 2-methyl-6-(phenylethynyl)-pyridine (MPEP), have been shown in small, randomized, controlled trials to have comparable efficacy to baclofen, but possibly a more favorable CNS side effect profile. Cannibinoid agonists, such as Delta(9)-THC, have also been demonstrated to reduce TLESRs and reflux events respectively. Macrolide antibiotics (eg, erythromycin) show early promise in a select group of patients with possible reflux associated post-lung transplant problems.

Cannabinoid-induced reduction in antral pacemaker frequency: a telemetric study in the ferret

BACKGROUND

The gastric myoelectric activity (GMA) is the electrical pacesetter potential, which drives gastric motility. Cannabinoids have broad-spectrum antiemetic and antinauseant activity. Paradoxically, they inhibit intestinal peristalsis and reduce gastric motility but their effect on GMA remains unknown.

METHODS

Ferrets were surgically implanted with radiotelemetry transmitters to record GMA, body temperature and heart rate. The effect of WIN 55,212-2 (1 mg kg(-1), i.p.), an agonist at the cannabinoid type 1 and 2 receptors was examined in conscious, unrestrained ferrets. WIN 55,212-2 was also compared to the anandamide upregulator URB 597 (5 mg kg(-1), i.p.) for a potential to modulate the emetic response and behavioral changes induced by apomorphine (0.25 mg kg(-1), s.c.).

KEY RESULTS

WIN 55,212-2 decreased GMA frequency (8.1 ± 0.4 cpm, compared to 9.6 ± 0.1 cpm in vehicle-treated animals, n = 6, P < 0.01). Apomorphine induced 9.0 ± 1.6 emetic episodes, WIN 55,212-2 inhibited the emetic response (3.3 ± 1.0 episodes, n = 6, P < 0.05) but URB 597 had no effect (9.0 ± 1.5 episodes). Apomorphine-induced hyperactivity in vehicle-treated animals (6.5 ± 3.6-16.6 ± 4.9 active behavior counts, n = 6, P < 0.01), which was reduced by WIN 55,212-2 (5.0 ± 1.5 counts, n = 6, P < 0.05).

CONCLUSIONS & INFERENCES

WIN 55,212-2 demonstrated clear antiemetic efficacy, which extends the broad-spectrum antiemetic efficacy of cannabinoids to dopamine receptor agonists in the ferret. Our results, however, suggest a more limited spectrum of action for URB 597. WIN 55,212-2 decreased the frequency of the antral electrical pacemaker, which reveals new insights into the mechanism regulating the decrease in motility induced by cannabinoids.

Mechanisms of Broad-Spectrum Antiemetic Efficacy of Cannabinoids against Chemotherapy-Induced Acute and Delayed Vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a complex pathophysiological condition and consists of two phases. The conventional CINV neurotransmitter hypothesis suggests that the immediate phase is mainly due to release of serotonin (5-HT) from the enterochromaffin cells in the gastrointestinal tract (GIT), while the delayed phase is a consequence of release of substance P (SP) in the brainstem. However, more recent findings argue against this simplistic neurotransmitter and anatomical view of CINV. Revision of the hypothesis advocates a more complex, differential and overlapping involvement of several emetic neurotransmitters/modulators (e.g. dopamine, serotonin, substance P, prostaglandins and related arachidonic acid derived metabolites) in both phases of emesis occurring concomitantly in the brainstem and in the GIT enteric nervous system (ENS) [1]. No single antiemetic is currently available to completely prevent both phases of CINV. The standard antiemetic regimens include a 5-HT₃ antagonist plus dexamethasone for the prevention of acute emetic phase, combined with an NK₁ receptor antagonist (e.g. aprepitant) for the delayed phase. Although NK₁ antagonists behave in animals as broad-spectrum antiemetics against different emetogens including cisplatin-induced acute and delayed vomiting, by themselves they are not very effective against CINV in cancer patients. Cannabinoids such as D⁸-THC also behave as broad-spectrum antiemetics against diverse emetic stimuli as well as being effective against both phases of CINV in animals and patients. Potential side effects may limit the clinical utility of direct-acting cannabinoid agonists which could be avoided by the use of corresponding indirect-acting agonists. Cannabinoids (both phyto-derived and synthetic) behave as agonist antiemetics via the activation of cannabinoid CB₁ receptors in both the brainstem and the ENS emetic loci. An endocannabinoid antiemetic tone may exist since inverse CB₁ agonists (but not the corresponding silent antagonists) cause nausea and vomiting.

New pharmacologic approaches in gastroesophageal reflux disease

This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.

Cannabinoid-Induced Hyperemesis: A Conundrum-From Clinical Recognition to Basic Science Mechanisms

Cannabinoids are used clinically on a subacute basis as prophylactic agonist antiemetics for the prevention of nausea and vomiting caused by chemotherapeutics. Cannabinoids prevent vomiting by inhibition of release of emetic neurotransmitters via stimulation of presynaptic cannabinoid CB₁ receptors. Cannabis-induced hyperemesis is a recently recognized syndrome associated with chronic cannabis use. It is characterized by repeated cyclical vomiting and learned compulsive hot water bathing behavior. Although considered rare, recent international publications of numerous case reports suggest the contrary. The syndrome appears to be a paradox and the pathophysiological mechanism(s) underlying the induced vomiting remains unknown. Although some traditional hypotheses have already been proposed, the present review critically explores the basic science of these explanations in the clinical setting and provides more current mechanisms for the induced hyperemesis. These encompass: (1) pharmacokinetic factors such as long half-life, chronic exposure, lipid solubility, individual variation in metabolism/excretion leading to accumulation of emetogenic cannabinoid metabolites, and/or cannabinoid withdrawal; and (2) pharmacodynamic factors including switching of the efficacy of Δ⁸-THC from partial agonist to antagonist, differential interaction of Δ⁸-THC with Gs and Gi signal transduction proteins, CB₁ receptor desensitization or downregulation, alterations in tissue concentrations of endocannabinoid agonists/inverse agonists, Δ⁸-THC-induced mobilization of emetogenic metabolites of the arachidonic acid cascade, brainstem versus enteric actions of Δ⁸-THC, and/or hypothermic versus hyperthermic actions of Δ⁸-THC. In addition, human and animal findings suggest that chronic exposure to cannabis may not be a prerequisite for the induction of vomiting but is required for the intensity of emesis.

Cannabinoids and the gut: new developments and emerging concepts

Cannabis has been used to treat gastrointestinal (GI) conditions that range from enteric infections and inflammatory conditions to disorders of motility, emesis and abdominal pain. The mechanistic basis of these treatments emerged after the discovery of Delta(9)-tetrahydrocannabinol as the major constituent of Cannabis. Further progress was made when the receptors for Delta(9)-tetrahydrocannabinol were identified as part of an endocannabinoid system, that consists of specific cannabinoid receptors, endogenous ligands and their biosynthetic and degradative enzymes. Anatomical, physiological and pharmacological studies have shown that the endocannabinoid system is widely distributed throughout the gut, with regional variation and organ-specific actions. It is involved in the regulation of food intake, nausea and emesis, gastric secretion and gastroprotection, GI motility, ion transport, visceral sensation, intestinal inflammation and cell proliferation in the gut. Cellular targets have been defined that include the enteric nervous system, epithelial and immune cells. Molecular targets of the endocannabinoid system include, in addition to the cannabinoid receptors, transient receptor potential vanilloid 1 receptors, peroxisome proliferator-activated receptor alpha receptors and the orphan G-protein coupled receptors, GPR55 and GPR119. Pharmacological agents that act on these targets have been shown in preclinical models to have therapeutic potential. Here, we discuss cannabinoid receptors and their localization in the gut, the proteins involved in endocannabinoid synthesis and degradation and the presence of endocannabinoids in the gut in health and disease. We focus on the pharmacological actions of cannabinoids in relation to GI disorders, highlighting recent data on genetic mutations in the endocannabinoid system in GI disease.

Roles of gastro-oesophageal afferents in the mechanisms and symptoms of reflux disease

Oesophageal pain is one of the most common reasons for physician consultation and/or seeking medication. It is most often caused by acid reflux from the stomach, but can also result from contractions of the oesophageal muscle. Different forms of pain are evoked by oesophageal acid, including heartburn and non-cardiac chest pain, but the basic mechanisms and pathways by which these are generated remain to be elucidated. Both vagal and spinal afferent pathways are implicated by basic research. The sensitivity of afferent fibres within these pathways may become altered after acid-induced inflammation and damage, but the severity of symptoms in humans does not necessarily correlate with the degree of inflammation. Gastro-oesophageal reflux disease (GORD) is caused by transient relaxations of the lower oesophageal sphincter, which are triggered by activation of gastric vagal mechanoreceptors. Vagal afferents are therefore an emerging therapeutic target for GORD. Pain in the absence of excess acid reflux remains a major challenge for treatment.

Mechanism of stretch-activated excitatory and inhibitory responses in the lower esophageal sphincter

We recently found that an orally directed stretch of the esophagus activates a neurally mediated relaxation of the lower esophageal sphincter (LES). Goals of our study were to characterize the neural mechanisms responsible for axial and transverse stretch-activated responses in the LES. LES pressure was monitored in anesthetized and artificially ventilated mice. Sutures were placed in the esophagus to exert graded stretch in the longitudinal and transverse directions. Effects of bilateral vagotomy and pharmacological agents on the stretch-activated LES responses were investigated. The relationship between vagally stimulated axial stretch and LES relaxation was also studied. Stretch in the longitudinal and transverse directions caused a dose-dependent LES relaxation and contraction, respectively, that were not affected by bilateral vagotomy and sympathectomy but were blocked by tetrodotoxin. In bilateral vagotomized animals, hexamethonium, atropine, pyridoxalphosphate-6-azophenyl-2',4' disulfonic acid (PPADS), and ondansetron did not block the stretch-activated LES relaxation and contraction. Axial stretch-activated LES relaxation was blocked by nitric oxide inhibitor and transverse stretch-activated LES contraction was blocked by a combination of atropine and substance P antagonist. Electrical stimulation of the vagus nerve induced LES relaxation and axial stretch on the LES, both of which were blocked by rocuronium. Axial and transverse stretch-activated LES relaxation and contraction were present in the W/W(v) mice that lack interstitial cells of Cajal (ICC). Stretch-activated LES relaxation and contraction are mediated through mechanosensitive neurons located in the myenteric plexus, which involves neither synaptic transmission nor ICC.

Effect of delta9-tetrahydrocannabinol, a cannabinoid receptor agonist, on the triggering of transient lower oesophageal sphincter relaxations in dogs and humans

BACKGROUND AND PURPOSE

Transient lower oesophageal sphincter relaxations (TLESRs) are the main mechanism underlying gastro-oesophageal reflux and are a potential pharmacological treatment target. We evaluated the effect of the CB(1)/CB(2) receptor agonist delta(9)-tetrahydrocannabinol (delta(9)-THC) on TLESRs in dogs. Based on these findings, the effect of delta(9)-THC was studied in healthy volunteers.

EXPERIMENTAL APPROACH

In dogs, manometry was used to evaluate the effect of delta(9)-THC in the presence and absence of the CB(1) receptor antagonist SR141716A on TLESRs induced by gastric distension. Secondly, the effect of 10 and 20 mg delta(9)-THC was studied in 18 healthy volunteers in a placebo-controlled study. Manometry was performed before and for 3 h after meal ingestion on three occasions.

KEY RESULTS

In dogs, delta(9)-THC dose-dependently inhibited TLESRs and reduced acid reflux rate. SR141716A significantly reversed the effects of delta(9)-THC on TLESRs. Similarly, in healthy volunteers, delta(9)-THC significantly reduced the number of TLESRs and caused a non-significant reduction of acid reflux episodes in the first postprandial hour. In addition, lower oesophageal sphincter pressure and swallowing were significantly reduced by delta(9)-THC. After intake of 20 mg, half of the subjects experienced nausea and vomiting leading to premature termination of the study. Other side-effects were hypotension, tachycardia and central effects.

CONCLUSIONS AND IMPLICATIONS

Delta(9)-THC significantly inhibited the increase in meal-induced TLESRs and reduced spontaneous swallowing in both dogs and humans. In humans, delta(9)-THC significantly reduced basal lower oesophageal sphincter pressure. These findings confirm previous observations in dogs and indicate that cannabinoid receptors are also involved in the triggering of TLESRs in humans.

Differential stimulatory effects of cannabinoids on VIP release and NO synthase activity in synaptosomal fractions from rat ileum

Cannabinoid-1 (CB1) and CB2 receptors are present on neurons of the enteric nervous system. Our aim was to study whether cannabinoid receptor activation is involved in the regulation of VIP release and NO synthesis in isolated fractions of nerve terminals from rat ileum. VIP was measured by RIA and NO synthesis was analyzed using a L-[3H]arginine assay. Anandamide stimulated VIP release (basal: 245.9+/-12.4pg/mg, 10(-6)M: 307.6+/-11.7pg/mg, [n=6, P<0.05], 10(-7)M: 367.0+/-26.1pg/mg, [n=6, P<0.01]). The cannabinoid receptor agonist WIN 55,212-2 had similar effects (basal: 250.5+/-37.4pg/mg, 10(-6)M: 320.9+/-34.7pg/mg; [n=4, P<0.05]). The stimulatory effect of anandamide was blocked by the selective CB2 receptor antagonist, SR144528 (10(-7)M) (anandamide 10(-6)M: 307.6+/-11.7pg/mg; +SR144528: 249.0+/-26.3pg/mg, [n=6, P<0.05]), whereas the selective CB1 receptor antagonist SR141716 A had no effect. NO synthesis was stimulated by anandamide ([fmol/mg/min] basal: 0.08+/-0.01, 10(-6)M: 0.16+/-0.03; 10(-7)M: 0.13+/-0.02, n=4, P<0.05) and WIN 55,212-2 ([fmol/mg/min] basal: 0.05+/-0.01, 10(-6)M: 0.1+/-0.02, n=4, P<0.05). The anandamide reuptake inhibitor, AM 404 increased basal NOS activity ([fmol/mg/min] control: 0.1+/-0.04, 10(-6)M: 0.28+/-0.08, n=7, P<0.05). The stimulatory effect of anandamide on NO synthase was not antagonized by antagonists at the CB1, CB2 or TRPV1 receptor, respectively. In conclusion, in enteric nerves anandamide stimulates VIP release by activation of a CB2 receptor specific pathway, while the stimulation of NO production suggests the existence of an additional type of cannabinoid receptor in the enteric nervous system.

Gastrointestinal endocannabinoid system: multifaceted roles in the healthy and inflamed intestine

1. The endogenous cannabinoid (endocannabinoid) system is emerging as a key modulator of intestinal physiology, influencing motility, secretion, epithelial integrity and immune function in the gut, in addition to influencing satiety and emesis. 2. Accumulating evidence suggests that the endocannabinoid system may play a pivotal role in the pathophysiology of gastrointestinal disease, particularly in the light of recent studies demonstrating an effect of endocannabinoids on the development of experimental inflammation and linkages with functional clinical disorders characterized by altered motility. 3. The predominant endocannabinoids, anandamide and 2-arachidonoylglycerol, not only mediate their effects via two recognized cannabinoid receptor subtypes, namely CB(1) and CB(2), but emerging evidence now shows they are also substrates for cyclo-oxygenase (COX)-2, generating a distinct and novel class of prostaglandin ethanolamides (prostamides) and prostaglandin glycerol esters. These compounds are bioactive and may mediate an array of biological effects distinct to those of conventional prostanoids. 4. The effects of prostamides on gastrointestinal motility, secretion, sensation and immune function have not been characterized extensively. Prostamides may play an important role in gastrointestinal inflammation, particularly given the enhanced expression of both COX-2 and endocannabinoids that occurs in the inflamed gut. 5. Further preclinical studies are needed to determine the therapeutic potential of drugs targeting the endocannabinoid system in functional and inflammatory gut disorders, to assist with the determination of feasibility for clinical translation.

Role of cannabinoid receptors in the control of gastrointestinal motility and perception

The identification of endocannabinoids and cannabinoid CB1 receptors in key areas of the intestinal wall, such as cholinergic neurons, supports a role for cannabinoids in the control of gastrointestinal motility. Activation of CB1 receptors inhibits the peristaltic reflex and slows down gastrointestinal and colonic transit. Endocannabinoids play an important inhibitory role in the control of the occurrence of transient lower esophageal sphincter relaxations. Cannabinoid receptor agonists inhibit gastric emptying and intestinal motility in humans. There is strong anatomical support for a role of CB1 receptors in the control of gastrointestinal perception, since these receptors have been identified in key sites of the neuronal circuitry involved in the transmission of visceral pain. Experimental data indicate a visceral antinociceptive action of cannabinoid receptor agonists, which remains to be confirmed in humans.

The role of endocannabinoids in the regulation of gastric emptying: alterations in mice fed a high-fat diet

BACKGROUND AND PURPOSE

Endocannabinoids (via cannabinoid CB(1) receptor activation) are physiological regulators of intestinal motility and food intake. However, their role in the regulation of gastric emptying is largely unexplored. The purpose of the present study was to investigate the involvement of the endocannabinoid system in the regulation of gastric emptying in mice fed either a standard diet (STD) or a high-fat diet (HFD) for 14 weeks.

EXPERIMENTAL APPROACH

Gastric emptying was evaluated by measuring the amount of phenol red recovered in the stomach after oral challenge; CB(1) expression was analysed by quantitative reverse transcription-PCR; endocannabinoid (anandamide and 2-arachidonoyl glycerol) levels were measured by liquid chromatography-mass spectrometry.

KEY RESULTS

Gastric emptying was reduced by anandamide, an effect counteracted by the CB(1) receptor antagonist rimonabant, but not by the CB(2) receptor antagonist SR144528 or by the transient receptor potential vanilloid type 1 (TRPV1) antagonist 5'-iodoresiniferatoxin. The fatty acid amide hydrolase (FAAH) inhibitor N-arachidonoyl-5-hydroxytryptamine (but not the anandamide uptake inhibitor OMDM-2) reduced gastric emptying in a way partly reduced by rimonabant. Compared to STD mice, HFD mice exhibited significantly higher body weight and fasting glucose levels, delayed gastric emptying and lower anandamide and CB(1) mRNA levels. N-arachidonoylserotonin (but not rimonabant) affected gastric emptying more efficaciously in HFD than STD mice.

CONCLUSIONS AND IMPLICATIONS

Gastric emptying is physiologically regulated by the endocannabinoid system, which is downregulated following a HFD leading to overweight.

Endocannabinoids and the gastrointestinal tract: what are the key questions?

Cannabinoid (CB1) receptor activation acts neuronally, reducing GI motility, diarrhoea, pain, transient lower oesophageal sphincter relaxations (TLESRs) and emesis, and promoting eating. CB2 receptor activation acts mostly via immune cells to reduce inflammation. What are the key questions which now need answering to further understand endocannabinoid pathophysiology? GPR55. Does this receptor have a GI role? Satiety, Nausea, Vomiting, Gastro-Oesophageal Reflux, Gastric Emptying. Endocannabinoids acting at CB1 receptors can increase food intake and body weight, exert anti-emetic activity, reduce gastric acid secretion and TLESRs; CB2 receptors may have a small role in emesis. Question 1: CB1 receptor activation reduces emesis and gastric emptying but the latter is associated with nausea. How is the paradox explained? Q2: Do non-CB receptor actions of endocannabinoids (for example TRPV1) also modulate emesis? Q3: Is pathology necessary (gastritis, gastro-oesophageal reflux) to observe CB2 receptor function? Intestinal Transit and Secretion. Reduced by endocannabinoids at CB1 receptors, but not by CB2 receptor agonists. Q1: Do the effects of endocannabinoids rapidly diminish with repeat-dosing? Q2: Do CB2 receptors need to be pathologically upregulated before they are active? Inflammation. CB1, CB2 and TRPV1 receptors may mediate an ability of endocannabinoids to reduce GI inflammation or its consequences. Q1: Are CB2 receptors upregulated by inflammatory or other pathology? Pain. Colonic bacterial flora may upregulate CB2 receptor expression and thereby increase intestinal sensitivity to noxious stimuli. Q1: Are CB2 receptors the interface between colonic bacteria and enteric- or extrinsic nerve sensitivity? Relevance of endocannabinoids to humans. Perhaps apart from appetite, this is largely unknown.

Involvement of cannabinoid receptors in inflammatory hypersensitivity to colonic distension in rats

Activation of cannabinoid CB1 and CB2 receptors is known to attenuate nociception and hyperalgesia in somatic inflammatory conditions. The aim of this study was to determine whether cannabinoids modulate colonic sensitivity in basal and inflammatory conditions. The effects of CB1 and CB2 receptor agonists and antagonists on the abdominal contractile response to colorectal distension (CRD) in basal conditions and after 2,4,6-trinitrobenzenesulphonic acid-induced colitis were investigated. As previously described, colitis triggered a hypersensitivity to CRD. In basal conditions, both CB1 (WIN 55212-2) and CB2 (JWH 015) agonists reduced the abdominal response to CRD at a dose of 1 mg kg(-1), i.p. Both compounds were active at a lower dose (0.1 mg kg(-1)) abolishing the hypersensitivity induced by colitis. Administered alone, CB1 (Rimonabant) and CB2 (SR 144528) receptor antagonists (10 mg kg(-1)) had no effect on basal sensitivity. In contrast, the CB1, but not the CB2, receptor antagonist enhanced colitis-induced hyperalgesia. It is concluded that colonic inflammation enhances the antinociceptive action of CB1 and CB2 receptor agonists, and activates an endogenous, CB1 receptor mediated, antinociceptive pathway.

Treatment of nausea and vomiting: gaps in our knowledge

The past 20 years have seen notable advances in our understanding of the physiology and pharmacology of the emetic reflex leading to the identification of the anti-emetic effects of 5-hydroxytryptamine(3) (5-HT(3)) and neurokinin(1) receptor (NK(1)) antagonists. The introduction of 5-HT(3) and NK(1) receptor antagonists into the clinic has had a major impact in alleviating the nausea and vomiting associated with the treatment of cancer and the sequelae to anaesthesia and surgery (post-operative nausea and vomiting, PONV). Despite these advances there are major gaps in our understanding. Interestingly, one of these is the relatively poor ability to treat nausea. Additional gaps in our knowledge are highlighted to provide a framework within which directions for research can be proposed. Particular attention is drawn to: lacunae in knowledge of some currently used anti-emetics such as the source of dopamine required to initiate emesis; the theoretical assumptions and mechanisms underlying the concept of a "universal anti-emetic"; the variety of receptors at which agonists act to have anti-emetic effects (GABA (B), CB(1), 5-HT(1A), ghrelin, opioid); issues of translation from animals to humans and the relationship between the pathways involved in emesis and certain gastrointestinal disorders such as dyspepsia and gastroesophageal reflux, with the latter being of particular interest as some agents affecting reflux are also anti-emetic. Together, the unmet clinical need to adequately control nausea, possibly by new drugs acting within the brainstem, and the significant gaps in understanding key aspects of the emetic reflex, suggest an important need to focus and re-direct research into the distressing and sometimes life-threatening symptoms of nausea and vomiting.

Methanandamide hyperpolarizes gastric arteries by stimulation of TRPV1 receptors on perivascular CGRP containing nerves

Endogenous as well as synthetic cannabinoids have potent vasodilatory actions in a variety of vascular preparations. Their precise mechanism of action is as yet unclear, but several studies point to the activation of type 1 vanilloid (TRPV1) receptors on primary afferent perivascular nerves, stimulating the release of calcitonin gene related peptide (CGRP). Given the documented gastroprotective function of these nerves, and the various gastrointestinal effects reported for cannabinoids, we explored a possible link between these systems in the gastric circulation by comparing responses of small gastric arteries to cannabinoids and to calcitonin gene related peptide using conventional microelectrode techniques. Exposure of small gastric arteries to the stable endocannabinoid analogue methanandamide caused a hyperpolarization of the vascular smooth muscle cells, which was completely abolished by the vanilloid receptor antagonist capsazepine (P < 0.01). Exposure to exogenous calcitonin gene related peptide evoked fully reproducible (P > 0.05) hyperpolarizations with similar time course, unaffected by capsazepine. Preincubation with glibenclamide, an inhibitor of ATP-sensitive potassium (KATP) channels, reversed both responses to methanandamide (P < 0.01) and calcitonin gene related peptide (P < 0.05). Similar results were found in rat mesenteric arteries. These findings show that cannabinoids stimulate TRPV1 receptors, presumably causing the release of calcitonin gene related peptide, which hyperpolarizes the smooth muscle cells by activation of KATP channels. Because membrane hyperpolarization is a powerful mediator of vasorelaxation, this novel pathway might prove to be an important mechanism affording gastroprotection.

Pharmacological targets in gastro-oesophageal reflux disease

Although proton pump inhibitors have become the mainstay of treatment in gastro-oesophageal reflux disease (GORD), there are still unmet needs in the management of this very common disorder. For example, all current proton pump inhibitors have a relatively slow onset of action and their activity is limited mainly to the post-prandial period with far less effective inhibition of nocturnal acid secretion. In order to achieve more potent, rapid and sustained acid inhibition several compounds are currently under development, such as new proton pump inhibitors with a prolonged plasma half-life, potassium competitive ATPase blockers (PCABs), histamine H3 agonists, and gastrin antagonists. Acid suppression does not, however, cure the disease and relapses are frequently observed after discontinuation of proton pump inhibitor therapy. Among the different abnormalities involved in the pathophysiology of this multifactorial disease, transient lower oesophageal sphincter relaxations represent the major mechanism responsible for episodes of reflux. Baclofen, the prototype GABA(B) receptor agonist, is one of the most potent inhibitors of transient lower oesophageal sphincter relaxations identified. To date the transfer of these relaxation-controlling pharmacological agents into clinical practice has however been hampered by the occurrence of unacceptable side effects. Beside "anti-relaxation therapy", the potential of novel prokinetics such as motilin agonists has been explored, especially since the motilin receptor has been cloned. Thus far the broad therapeutic value of prokinetics in GORD does, however, seem very limited in terms of efficacy with respect to oesophageal motility and acid exposure. Lastly, further research is necessary to better understand the complex mechanisms involved in oesophageal sensitivity and mucosal defence.

Transient lower esophageal sphincter relaxations in dogs are inhibited by a metabotropic glutamate receptor 5 antagonist

Transient lower esophageal sphincter relaxation is the major mechanism for gastroesophageal reflux. The present study was initiated to investigate the potential effect of the metabotropic glutamate 5 (mGlu5) receptor antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), on transient lower esophageal sphincter relaxations in the conscious dog. MPEP (1.4-8.7 micromol/kg i.v.) produced a dose-dependent inhibition of transient lower esophageal sphincter relaxations (59+/-11% inhibition at 8.7 micromol/kg). In addition, there was a reduction of the number of reflux episodes and an increase in latency time to the occurrence of the first transient lower esophageal sphincter relaxation. No effect was seen on basal lower esophageal sphincter pressure or on swallowing. It is concluded that the mGlu5 receptor antagonist MPEP potently inhibits transient lower esophageal sphincter relaxations and that the mGlu5 receptor is a potential target for treatment of gastroesophageal reflux disease.

Review article: endocannabinoids and their receptors in the enteric nervous system

The therapeutic actions of cannabinoids have been known for centuries. In the last 25 years this area of research has grown exponentially with the discovery of specific cannabinoid receptors and endogenous ligands. In the enteric nervous system of gastrointestinal tract, cannabinoid receptors are located on enteric nerve terminals where they exert inhibitory actions on neurotransmission to reduce motility and secretion. Endogenous cannabinoids are present in the enteric nervous system, as are the degradative enzymes necessary to inhibit their action. The cellular mechanism of action of endocannabinoids has not been established in the enteric nervous system. Endocannabinoids not only act at cannabinoid receptors, but potentially also at vanilloid and 5-HT3 receptors, both of which are expressed in the gastrointestinal tract. The interactions between endocannabinoids and these other important receptor systems have not been extensively investigated. A greater understanding of the endocannabinoid system in the enteric nervous system could lead to advances with important therapeutic potential in the treatment of gastrointestinal disorders such as irritable bowel syndrome, inflammatory bowel disease, secretory diarrhoea and gastro-oesophageal reflux disease.