Defaecation, intestinal fluid accumulation and motility in rodents: implications of cannabinoid CB1 receptors

Cannabinoids: A Guide for Use in the World of Gastrointestinal Disease

Cannabinoids have been known as the primary component of cannabis for decades, but the characterization of the endocannabinoid system (ECS) in the 1990s opened the doors for cannabis' use in modern medicine. The 2 main receptors of this system, cannabinoid receptors 1 and 2, are found on cells of various tissues, with significant expression in the gastrointestinal (GI) tract. The characterization of the ECS also heralded the understanding of endocannabinoids, naturally occurring compounds synthesized in the human body. Via secondary signaling pathways acting on vagal nerves, nociceptors, and immune cells, cannabinoids have been shown to have both palliative and detrimental effects on the pathophysiology of GI disorders. Although research on the effects of both endogenous and exogenous cannabinoids has been slow due to the complicated legal history of cannabis, discoveries of cannabinoids' treatment potential have been found in various fields of medicine, including the GI world. Medical cannabis has since been offered as a treatment for a myriad of conditions and malignancies, including cancer, human immunodeficiency virus/acquired immunodeficiency syndrome, multiple sclerosis, chronic pain, nausea, posttraumatic stress disorder, amyotrophic lateral sclerosis, cachexia, glaucoma, and epilepsy. This article hopes to create an overview of current research on cannabinoids and the ECS, detail the potential advantages and pitfalls of their use in GI diseases, and explore possible future developments in this field.

Rimonabant, a potent CB1 cannabinoid receptor antagonist, is a Gαi/o protein inhibitor

Rimonabant is a potent and selective cannabinoid CB1 receptor antagonist widely used in animal and clinical studies. Besides its antagonistic properties, numerous studies have shown that, at micromolar concentrations rimonabant behaves as an inverse agonist at CB1 receptors. The mechanism underpinning this activity is unclear. Here we show that micromolar concentrations of rimonabant inhibited Gα_i/o-type G proteins, resulting in a receptor-independent block of G protein signaling. Accordingly, rimonabant decreased basal and agonist stimulated [³⁵S]GTPγS binding to cortical membranes of CB1- and GABA_B-receptor KO mice and Chinese Hamster Ovary (CHO) cell membranes stably transfected with GABA_B or D2 dopamine receptors. The structural analog of rimonabant, AM251, decreased basal and baclofen-stimulated GTPγS binding to rat cortical and CHO cell membranes expressing GABA_B receptors. Rimonabant prevented G protein-mediated GABA_B and D2 dopamine receptor signaling to adenylyl cyclase in Human Embryonic Kidney 293 cells and to G protein-coupled inwardly rectifying K⁺ channels (GIRK) in midbrain dopamine neurons of CB1 KO mice. Rimonabant suppressed GIRK gating induced by GTPγS in CHO cells transfected with GIRK, consistent with a receptor-independent action. Bioluminescent resonance energy transfer (BRET) measurements in living CHO cells showed that, in presence or absence of co-expressed GABA_B receptors, rimonabant stabilized the heterotrimeric Gαi/o-protein complex and prevented conformational rearrangements induced by GABA_B receptor activation. Rimonabant failed to inhibit Gαs-mediated signaling, supporting its specificity for Gα_i/o-type G proteins. The inhibition of Gα_i/o protein provides a new site of rimonabant action that may help to understand its pharmacological and toxicological effects occurring at high concentrations.

Novel derivatives of 1,2,3-triazole, cannabinoid-1 receptor ligands modulate gastrointestinal motility in mice

Cannabinoid-1 (CB1) receptors are broadly distributed in the central and peripheral nervous systems; among others, they are located in the enteric nervous system. In the gastrointestinal (GI) system, they participate in regulation of intestinal motility or ion transport. The aim of our study was to assess the effect of 1,2,3-triazole derivatives (compound 1: 2-[4,5-bis(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]-N-(2-fluorobenzyl)acetamide, compound 2: 2-[4,5-bis(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]-N-(4-fluorobenzyl)acetamide, compound 3: N-benzyl-2-[4-(4-chlorophenyl)-5-(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]acetamide]), characterized in vitro as CB1 antagonists with high CB1 over CB2 selectivity, in the mouse GI tract. The action of compounds 1-3 was assessed in vitro (electrical field stimulated smooth muscle contractility of the mouse ileum and colon) and in vivo (whole GI transit time). Compound 1 decreased ileal (10^-6 M) and colonic (10^-7-10^-6 M) smooth muscles contractility. Moreover, it prolonged whole GI transit. Compound 2 (10^-10-10^-8 M) slightly increased the amplitude of muscle contractions in the ileum, but at a higher concentration (10^-6 M), the amplitude was decreased. Compound 2 reduced colonic contractility but accelerated GI transit. Compound 3 decreased the amplitude of intestinal muscle contractions in the ileum (10^-6 M) and colon (10^-10-10^-6 M). Moreover, it increased the GI transit time in vivo. Triazole derivatives possess easily modifiable structure and interesting pharmacological action in the GI tract; further, alterations may enhance their efficacy at CB receptors and provide low side effect profile in clinical conditions.

Complementary and Alternative Medicine Strategies for Therapeutic Gut Microbiota Modulation in Inflammatory Bowel Disease and their Next-Generation Approaches

The human gut microbiome exerts a major impact on human health and disease, and therapeutic gut microbiota modulation is now a well-advocated strategy in the management of many diseases, including inflammatory bowel disease (IBD). Scientific and clinical evidence in support of complementary and alternative medicine, in targeting intestinal dysbiosis among patients with IBD, or other disorders, has increased dramatically over the past years. Delivery of "artificial" stool replacements for fecal microbiota transplantation (FMT) could provide an effective, safer alternative to that of human donor stool. Nevertheless, optimum timing of FMT administration in IBD remains unexplored, and future investigations are essential.

Endocannabinoids in the Gut

Cannabis has been used medicinally for centuries to treat a variety of disorders, including those associated with the gastrointestinal tract. The discovery of our bodies' own "cannabis-like molecules" and associated receptors and metabolic machinery - collectively called the endocannabinoid system - enabled investigations into the physiological relevance for the system, and provided the field with evidence of a critical function for this endogenous signaling pathway in health and disease. Recent investigations yield insight into a significant participation for the endocannabinoid system in the normal physiology of gastrointestinal function, and its possible dysfunction in gastrointestinal pathology. Many gaps, however, remain in our understanding of the precise neural and molecular mechanisms across tissue departments that are under the regulatory control of the endocannabinoid system. This review highlights research that reveals an important - and at times surprising - role for the endocannabinoid system in the control of a variety of gastrointestinal functions, including motility, gut-brain mediated fat intake and hunger signaling, inflammation and gut permeability, and dynamic interactions with gut microbiota.

Prevention of Diet-Induced Obesity Effects on Body Weight and Gut Microbiota in Mice Treated Chronically with Δ9-Tetrahydrocannabinol

Objective

Acute administration of cannabinoid CB₁ receptor agonists, or the ingestion of cannabis, induces short-term hyperphagia. However, the incidence of obesity is lower in frequent cannabis users compared to non-users. Gut microbiota affects host metabolism and altered microbial profiles are observed in obese states. Gut microbiota modifies adipogenesis through actions on the endocannabinoid system. This study investigated the effect of chronic THC administration on body weight and gut microbiota in diet-induced obese (DIO) and lean mice.

Methods

Adult male DIO and lean mice were treated daily with vehicle or THC (2mg/kg for 3 weeks and 4 mg/kg for 1 additional week). Body weight, fat mass, energy intake, locomotor activity, whole gut transit and gut microbiota were measured longitudinally.

Results

THC reduced weight gain, fat mass gain and energy intake in DIO but not lean mice. DIO-induced changes in select gut microbiota were prevented in mice chronically administered THC. THC had no effect on locomotor activity or whole gut transit in either lean or DIO mice.

Conclusions

Chronic THC treatment reduced energy intake and prevented high fat diet-induced increases in body weight and adiposity; effects that were unlikely to be a result of sedation or altered gastrointestinal transit. Changes in gut microbiota potentially contribute to chronic THC-induced actions on body weight in obesity.

Monoglyceride lipase deficiency causes desensitization of intestinal cannabinoid receptor type 1 and increased colonic μ-opioid receptor sensitivity

Background and Purpose

Monoglyceride lipase (MGL) degrades 2-arachidonoyl glycerol (2-AG), an endogenous agonist of cannabinoid receptors (CB_1/2). Because the CB₁ receptor is involved in the control of gut function, we investigated the effects of pharmacological inhibition and genetic deletion of MGL on intestinal motility. Furthermore, we determined whether defective 2-AG degradation affects μ-opioid receptor (μ receptor) signalling, a parallel pathway regulating gut motility.

Experimental Approach

Gut motility was investigated by monitoring Evans Blue transit and colonic bead propulsion in response to MGL inhibition and CB₁ receptor or μ receptor stimulation. Ileal contractility was investigated by electrical field stimulation. CB₁ receptor expression in ileum and colon was assessed by immunohistochemical analyses.

Key Results

Pharmacological inhibition of MGL slowed down whole gut transit in a CB₁ receptor-dependent manner. Conversely, genetic deletion of MGL did not affect gut transit despite increased 2-AG levels. Notably, MGL deficiency caused complete insensitivity to CB₁ receptor agonist-mediated inhibition of whole gut transit and ileal contractility suggesting local desensitization of CB₁ receptors. Accordingly, immunohistochemical analyses of myenteric ganglia of MGL-deficient mice revealed that CB₁ receptors were trapped in endocytic vesicles. Finally, MGL-deficient mice displayed accelerated colonic propulsion and were hypersensitive to μ receptor agonist-mediated inhibition of colonic motility. This phenotype was reproduced by chronic pharmacological inhibition of MGL.

Conclusion and Implications

Constantly elevated 2-AG levels induce severe desensitization of intestinal CB₁ receptors and increased sensitivity to μ receptor-mediated inhibition of colonic motility. These changes should be considered when cannabinoid-based drugs are used in the therapy of gastrointestinal diseases.

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.

Rimonabant, gastrointestinal motility and obesity

Background:

Obesity and overweight affect more than half of the US population and are associated with a number of diseases. Rimonabant, a cannabinoid receptor 1 blocker in the endocannabinoid (EC) system, was indicated in Europe for the treatment of obesity and overweight patients with associated risk factors but withdrawn on Jan, 2009 because of side effects. Many studies have reported the effects of rimonabant on gastrointestinal (GI) motility and food intake.

The aims of this review are:

to review the relationship of EC system with GI motility and food intake;

to review the studies of rimonabant on GI motility, food intake and obesity;

and to report the tolerance and side effects of rimonabant.

Methods:

the literature (Pubmed database) was searched using keywords: rimonabant, obesity and GI motility.

Results:

GI motility is related with appetite, food intake and nutrients absorption. The EC system inhibits GI motility, reduces emesis and increases food intake; Rimonabant accelerates gastric emptying and intestinal transition but decreases energy metabolism and food intake. There is rapid onset of tolerance to the prokinetic effect of rimonabant. The main side effects of rimonabant are depression and GI symptoms.

Conclusions:

Rimonabant has significant effects on energy metabolism and food intake, probably mediated via its effects on GI motility.

Molecular imaging of inflammation in inflammatory bowel disease with a clinically translatable dual-selectin-targeted US contrast agent: comparison with FDG PET/CT in a mouse model

PURPOSE

To develop and test a molecular imaging approach that uses ultrasonography (US) and a clinically translatable dual-targeted (P- and E-selectin) contrast agent (MBSelectin) in the quantification of inflammation at the molecular level and to quantitatively correlate selectin-targeted US with fluorodeoxyglucose (FDG) combined positron emission tomography (PET) and computed tomography (CT) in terms of visualization and quantification of different levels of inflammation in a murine acute colitis model.

MATERIALS AND METHODS

Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. MBSelectin was developed by covalently binding an analog of the naturally occurring binding ligand P-selectin glycoprotein ligand 1 fused to a human fragment crystallizable(or Fc) domain onto the lipid shell of perfluorobutane and nitrogen-containing MBs. Binding specificity of MBSelectin was assessed in vitro with a flow chamber assay and in vivo with a chemically induced acute colitis murine model. US signal was quantitatively correlated with FDG uptake at PET/CT and histologic grade. Statistical analysis was performed with the Student t test, analysis of variance, and Pearson correlation analysis.

RESULTS

MBSelectin showed strong attachment to both human and mouse P- and E-selectin compared with MBControl in vitro (P ≤ .002). In vivo, US signal was significantly increased (P < .001) in mice with acute colitis (173.8 arbitrary units [au] ± 134.8 [standard deviation]) compared with control mice (5.0 au ± 4.5). US imaging signal strongly correlated with FDG uptake on PET/CT images (ρ = 0.89, P < .001). Ex vivo analysis enabled confirmation of inflammation in mice with acute colitis and high expression levels of P- and E-selectin in mucosal capillaries (P = .014).

CONCLUSION

US with MBSelectin specifically enables detection and quantification of inflammation in a murine acute colitis model, leveraging the natural pathway of leukocyte recruitment in inflammatory tissue. US imaging with MBSelectin correlates well with FDG uptake at PET/CT imaging.

Mangiferin, a natural xanthone, accelerates gastrointestinal transit in mice involving cholinergic mechanism

AIM: To investigate the effects of mangiferin on gastrointestinal transit (GIT) in normal and constipated mice, together with the possible mechanism.

METHODS: Intragastrically-administered charcoal meal was used to measure GIT in overnight starved Swiss mice. In the first experiments, mangiferin (3 mg/kg, 10 mg/kg, 30 mg/kg, and 100 mg/kg, po) or tegaserod (1 mg/kg, ip) were administered 30 min before the charcoal meal to study their effects on normal transit. In the second series, mangiferin (30 mg/kg) was tested on delayed GIT induced by several different pharmacological agonists (morphine, clonidine, capsaicin) or antagonists (ondansetron, verapamil, and atropine) whereas in the third series, mangiferin (30 mg/kg, 100 mg/kg and 300 mg/kg) or tegaserod (1 mg/kg) were tested on 6 h fecal pellets outputted by freely fed mice. The ratio of wet to dry weight was calculated and used as a marker of fecal water content.

RESULTS: Mangiferin administered orally significantly (P < 0.05) accelerated GIT at 30 mg/kg and 100 mg/kg (89% and 93%, respectively), similarly to 5-hydroxytryptamine₄ (5-HT₄) agonist tegaserod (81%) when compared to vehicle-treated control (63%). Co-administered mangiferin (30 mg/kg) totally reversed the inhibitory effect of opioid agonist morphine, 5-HT₃-receptor antagonist ondansetron and transient receptor potential vanilloid-1 receptor agonist capsaicin on GIT, but only to a partial extent with the GIT-delay induced by α₂-adrenoceptor agonist clonidine, and calcium antagonist verapamil. However, co-administered atropine completely blocked the stimulant effect of mangiferin on GIT, suggesting the involvement of muscarinic acetylcholine receptor activation. Although mangiferin significantly enhanced the 6 h fecal output at higher doses (245.5 ± 10.43 mg vs 161.9 ± 10.82 mg and 227.1 ± 20.11 mg vs 161.9 ± 10.82 mg of vehicle-treated control, at 30 and 100 mg/kg, P < 0.05, respectively), the effect of tegaserod was more potent (297.4 ± 7.42 mg vs 161.9 ± 10.82 mg of vehicle-treated control, P < 0.05). Unlike tegaserod, which showed an enhanced water content in fecal pellets (59.20% ± 1.09% vs 51.44% ± 1.19% of control, P < 0.05), mangiferin evidenced no such effect, indicating that it has only a motor and not a secretomotor effect.

CONCLUSION: Our data indicate the prokinetic action of mangiferin. It can stimulate the normal GIT and also overcome the drug-induced transit delay, via a cholinergic physiological mechanism.

Pharmacogenetic trial of a cannabinoid agonist shows reduced fasting colonic motility in patients with nonconstipated irritable bowel syndrome

BACKGROUND & AIMS

Cannabinoid receptors are located on cholinergic neurons. Genetic variants that affect endocannabinoid metabolism are associated with colonic transit in patients with irritable bowel syndrome (IBS) with diarrhea. We compared the effects of dronabinol, a nonselective agonist of the cannabinoid receptor, with those of placebo on colonic motility and sensation in patients with IBS, and examined the effects of IBS subtype and specific genetic variants in cannabinoid mechanisms.

METHODS

Seventy-five individuals with IBS (35 with IBS with constipation, 35 with IBS with diarrhea, and with 5 IBS alternating) were randomly assigned to groups that were given 1 dose of placebo or 2.5 mg or 5.0 mg dronabinol. We assessed left colonic compliance, motility index (MI), tone, and sensation during fasting and after a meal. We analyzed the single nucleotide polymorphisms CNR1 rs806378, fatty acid amide hydrolase (FAAH) rs324420, and MGLL rs4881.

RESULTS

In all patients, dronabinol decreased fasting proximal left colonic MI compared with placebo (overall P = .05; for 5 mg dronabinol, P = .046), decreased fasting distal left colonic MI (overall P = .08; for 5 mg, P = .13), and increased colonic compliance (P = .058). The effects of dronabinol were greatest in patients with IBS with diarrhea or IBS alternating (proximal colonic MI, overall P = .022; compliance, overall P = .03). Dronabinol did not alter sensation or tone. CNR1 rs806378 (CC vs CT/TT) appeared to affect fasting proximal MI in all patients with IBS (P = .075). Dronabinol affected fasting distal MI in patients, regardless of FAAH rs324420 variant (CA/AA vs CC) (P = .046); the greatest effects were observed among IBS with constipation patients with the FAAH CC variant (P = .045). Dronabinol affected fasting proximal MI in patients with IBS with diarrhea or alternating with the variant FAAH CA/AA (P = .013).

CONCLUSIONS

In patients with IBS with diarrhea or alternating, dronabinol reduces fasting colonic motility; FAAH and CNR1 variants could influence the effects of this drug on colonic motility.

Muscarinic receptor subtypes involved in regulation of colonic motility in mice: functional studies using muscarinic receptor-deficient mice

Although muscarinic M(2) and M(3) receptors are known to be important for regulation of gastric and small intestinal motility, muscarinic receptor subtypes regulating colonic function remain to be investigated. The aim of this study was to characterize muscarinic receptors involved in regulation of colonic contractility. M(2) and/or M(3) receptor knockout (KO) and wild-type mice were used in in vivo (defecation, colonic propulsion) and in vitro (contraction) experiments. Amount of feces was significantly decreased in M(3)R-KO and M(2)/M(3)R-KO mice but not in M(2)R-KO mice. Ranking of colonic propulsion was wild-type=M(2)R-KO>M(3)R-KO>M(2)/M(3)R-KO. In vitro, the amplitude of migrating motor complexes in M(2)R-KO, M(3)R-KO and M(2)/M(3)R-KO mice was significantly lower than that in wild-type mice. Carbachol caused concentration-dependent contraction of the proximal colon and distal colon from wild-type mice. In M(2)R-KO mice, the concentration-contraction curves shifted to the right and downward. In contrast, carbachol caused non-sustained contraction and relaxation in M(3)R-KO mice depending on its concentration. Carbachol did not cause contraction but instead caused relaxation of colonic strips from M(2)/M(3)R-KO mice. 4-[[[(3-chlorophenyl)amino]carbonyl]oxy]-N,N,N-trimethyl-2-butyn-1-aminium chloride (McN-A-343) caused a non-sustained contraction of colonic strips from wild-type mice, and this contraction was changed to a sustained contraction by tetrodotoxin, pirenzepine and L-nitroarginine methylester (L-NAME). In the colon of M(2)/M(3)R-KO mice, McN-A-343 caused only relaxation, which was decreased by tetrodotoxin, pirenzepine and L-NAME. In conclusion, M(1), M(2) and M(3) receptors regulate colonic motility of the mouse. M(2) and M(3) receptors mediate cholinergic contraction, but M(1) receptors on inhibitory nitrergic nerves counteract muscarinic contraction.

Guinea pig ileum motility stimulation elicited by N-formyl-Met-Leu-Phe (fMLF) involves neurotransmitters and prostanoids

In guinea-pig ileum (GPI), the chemotactic peptide N-formyl-Met-Leu-Phe-OH (fMLF) possesses spasmogenic properties through the activation of formyl peptide receptors (FPRs). Despite this, the mediators involved remain to be elucidated. fMLF (1nM-1μM) induced a dose-dependent contraction of GPI (EC(50)=24nM), that is blocked by pre-treatment with the FPRs antagonist Boc(2). The pre-treatment with tetrodotoxin (TTX) atropine or with SR140333 reduced the fMLF-induced contraction, whereas with hexamethonium, MEN10627, SB222200, mepyramine, cimetidine, thioperamide or methysergide did not produce any effect. With DuP697 pre-treatment, but not with piroxicam, reduced the fMLF-induced contraction. After stimulation with 24nM fMLF, a strong increase in the PGE(2) levels was observed. Finally, the concomitant blocking of the NK(1) receptor, the muscarinic receptors and COX-2 abolished the GPI contractions induced by fMLF. fMLF induced a concentration-dependent contraction of guinea-pig jejunum (EC(50)=11nM), proximal colon (EC(50)=3.5nM) and distal colon (EC(50)=2.2nM), with a time-course similar to that observed in GPI. In these preparations as well, the co-administration of atropine, SR140333 and DuP697 abolished the contractions induced by fMLF. Intraperitoneal injection of fMLF (0.1 or 1μmol/kg) enhanced the gastrointestinal motility in mice, abolished by the co-administration of atropine, SR140333 and DuP697. In conclusion, we showed that fMLF exerts spasmogenic actions on guinea-pig intestine both in vitro and in vivo through the release of acetylcholine and substance P from myenteric motorneurons and through prostanoids, probably from the inflammatory cells of the enteric immune system.

Evidence for both inverse agonism at the cannabinoid CB1 receptor and the lack of an endogenous cannabinoid tone in the rat and guinea-pig isolated ileum myenteric plexus-longitudinal muscle preparation

BACKGROUND AND PURPOSE

Cannabinoid receptor agonists reduce intestinal propulsion in rodents through the CB(1) receptor. In addition to its antagonistic activity at this receptor, rimonabant (N-(piperidino)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxyamide) alone augments intestinal transit. Using rat and guinea-pig ileum MPLM (myenteric plexus-longitudinal muscle) preparations, we investigated whether the latter effect was through inverse agonism or antagonism of endocannabinoid agonist(s).

EXPERIMENTAL APPROACH

Inverse agonism was investigated by comparing the maximal enhancement of electrically evoked contractions of the MPLM by two CB(1) receptor antagonists, AM 251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) and O-2050 [(6aR,10aR)-3-(1-methanesulphonylamino-4-hexyn-6-yl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6-H-dibenzo[b,d]pyran], with that produced by rimonabant. To reveal ongoing endocannabinoid activity, effects of inhibiting endocannabinoid hydrolysis by fatty acid amide hydrolase (FAAH) using AA-5HT (arachidonyl-5-hydroxytryptamine), PMSF (phenylmethylsulphonyl fluoride) or URB-597 (3'-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate), or putative uptake using VDM-11 [(5Z,8Z,11Z,14Z)-N-(4-hydroxy-2-methylphenyl)-5,8,11,14-eicosatetraenamide] was evaluated.

KEY RESULTS

The presence of CB(1) receptors was revealed by antagonism of exogenous anandamide, arachidonylethanolamide (AEA) and WIN 55,212-2 [(R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)-pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate] by rimonabant. The rank order of potentiation of contractions was AM 251 > rimonabant > O-2050. Neither the FAAH inhibitors nor VDM-11 affected electrically evoked contractions. Each FAAH inhibitor increased the potency of AEA but not WIN 55,212-2. VDM-11 did not alter the inhibitory effect of AEA.

CONCLUSIONS AND IMPLICATIONS

The different levels of maximal potentiation of contractions by the CB(1) receptor antagonists suggest inverse agonism. The potentiation of the action of AEA by the FAAH inhibitors showed that FAAH was present. The lack of effect of FAAH inhibitors and VDM-11 alone on electrically evoked contractions, and on the potency of exogenous AEA suggests that pharmacologically active endocannabinoids were not released and the endocannabinoid transporter was absent. Thus, the CB(1) receptor antagonists behave as inverse agonists.

Differential effects of CB(1) neutral antagonists and inverse agonists on gastrointestinal motility in mice

BACKGROUND

Cannabinoid type 1 (CB(1)) receptors are involved in the regulation of gastrointestinal (GI) motility and secretion. Our aim was to characterize the roles of the CB(1) receptor on GI motility and secretion in vitro and in vivo by using different classes of CB(1) receptor antagonists.

METHODS

Immunohistochemistry was used to examine the localization of CB(1) receptor in the mouse ileum and colon. Organ bath experiments on mouse ileum and in vivo motility testing comprising upper GI transit, colonic expulsion, and whole gut transit were performed to characterize the effects of the inverse agonist/antagonist AM251 and the neutral antagonist AM4113. As a marker of secretory function we measured short circuit current in vitro using Ussing chambers and stool fluid content in vivo in mouse colon. We also assessed colonic epithelial permeability in vitro using FITC-labeled inulin.

KEY RESULTS

In vivo, the inverse agonist AM251 increased upper GI transit and whole gut transit, but it had no effect on colonic expulsion. By contrast, the neutral antagonist AM4113 increased upper GI transit, but unexpectedly reduced both colonic expulsion and whole gut transit at high, but not lower doses.

CONCLUSIONS & INFERENCES

Cannabinoid type 1 receptors regulate small intestinal and colonic motility, but not GI secretion under physiological conditions. Cannabinoid type 1 inverse agonists and CB(1) neutral antagonists have different effects on intestinal motility. The ability of the neutral antagonist not to affect whole gut transit may be important for the future development of CB(1) receptor antagonists as therapeutic agents.

Naphthalen-1-yl-(4-pentyloxynaphthalen-1-yl)methanone (SAB378), a peripherally restricted cannabinoid CB1/CB2 receptor agonist, inhibits gastrointestinal motility but has no effect on experimental colitis in mice

The endocannabinoid system is involved in the regulation of gastrointestinal (GI) motility and inflammation. Using the peripherally restricted cannabinoid (CB)(1)/CB(2) receptor agonist naphthalen-1-yl-(4-pentyloxynaphthalen-1-yl)methanone (SAB378), we investigated the role of peripheral cannabinoid receptors in the regulation of GI motility and the development of colitis in mice. The actions of SAB378 on whole gut transit, upper GI transit, colonic propulsion, and locomotor activity were investigated in C57BL/6N, CB(1) receptor knockout, and CB(2) receptor knockout mice. The potential for SAB378 to modify inflammation was studied by using dextran sulfate sodium (DSS) and 2,4,6-trinitrobenzene sulfonic acid (TNBS) models of experimental colitis. SAB378 did not modify locomotor activity. SAB378 slowed all parameters of GI motility, and these effects were significantly reduced by the CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3 carboxamide (AM251), but not by the CB(2) receptor antagonist 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H- indol-3-yl](4-methoxyphenyl)methanone (AM630). SAB378 did not inhibit GI transit or colonic propulsion in CB(1) receptor knockout mice, whereas its effects were observed in CB(2) receptor knockout mice. SAB378 did not reduce the degree of colitis induced by DSS or TNBS. The actions of SAB378 on GI motility are mediated by peripherally located CB(1) receptors. SAB378 was not effective against two models of experimental colitis, which may indicate that peripheral cannabinoid receptor stimulation alone may not be sufficient to mediate the anti-inflammatory effects of cannabinoids.

Involvement of cannabinoid-1 and cannabinoid-2 receptors in septic ileus

BACKGROUND Cannabinoid (CB) receptors are involved in the regulation of gastrointestinal (GI) motility under physiological and pathophysiological conditions. We aimed to characterize the possible influence of CB(1) and CB(2) receptors on motility impairment in a model of septic ileus. METHODS Lipopolysaccharide (LPS) injections were used to mimic pathophysiological features of septic ileus. Spontaneous jejunal myoelectrical activity was measured in rats in vivo, and upper GI transit was measured in vivo by gavaging of a charcoal marker into the stomach of mice, in absence or presence of LPS, and CB(1) and CB(2) receptor agonists and antagonists. Tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 levels were measured using enzyme-linked immunosorbent assay. Histology was performed with haematoxylin-eosin staining. KEY RESULTS Lipopolysaccharide treatment significantly reduced amplitude and frequency of myoelectric spiking activity and GI transit in vivo in a dose-dependent manner. TNF-alpha and IL-6 were increased in LPS-treated animals and histology showed oedema and cell infiltration. Both, the CB(1) agonist HU210 and the CB(2) agonist JWH133 reduced myoelectrical activity whereas the CB(1) antagonist AM251 caused an increase of myoelectrical activity. Pretreatment with AM251 or AM630 prevented against LPS-induced reduction of myoelectrical activity, and also against the delay of GI transit during septic ileus in vivo. CONCLUSIONS & INFERENCES The LPS model of septic ileus impairs jejunal myoelectrical activity and delays GI transit in vivo. Antagonists at the CB(1) receptor or the CB(2) receptor prevent the delay of GI transit and thus may be powerful tools in the future treatment of septic ileus.

Interaction between cannabinoid CB1 receptors and endogenous ATP in the control of spontaneous mechanical activity in mouse ileum

BACKGROUND AND PURPOSE

Although it is well accepted that cannabinoids modulate intestinal motility by reducing cholinergic neurotransmission mediated by CB(1) receptors, it is not known whether the endocannabinoids are involved in more complex circuits and if they interact with other systems. The aim of the present study was to examine possible interactions between cannabinoid CB(1) receptors and purines in the control of spontaneous contractility of longitudinal muscle in mouse ileum.

EXPERIMENTAL APPROACH

The mechanical activity of longitudinally oriented ileal segments from mice was recorded as isometric contractions.

KEY RESULTS

The selective CB(1) receptor agonist, N-(2-chloroethyl)5,8,11,14-eicosaetraenamide (ACEA) reduced, concentration dependently, spontaneous contractions in mouse ileum. This effect was almost abolished by tetrodotoxin (TTX) or atropine. Inhibition by ACEA was not affected by theophylline (P1 receptor antagonist) or by P2Y receptor desensitization with adenosine 5'[beta-thio]diphosphate trilithium salt, but was significantly reversed by pyridoxal phosphate-6-azo(benzene-2,4-disulphonic acid) (P2 receptor antagonist), by P2X receptor desensitization with alpha,beta-methyleneadenosine 5'-triphosphate lithium salt (alpha,beta-MeATP) or by 8,8'-[carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino) bis(1,3,5-naphthalenetrisulphonic acid)] (P2X receptor antagonist). Contractile responses to alpha,beta-MeATP (P2X receptor agonist) were virtually abolished by TTX or atropine, suggesting that they were mediated by acetylcholine released from neurones, and significantly reduced by ACEA.

CONCLUSION AND IMPLICATIONS

In mouse ileum, activation of CB(1) receptors, apart from reducing acetylcholine release from cholinergic nerves, was able to modulate negatively, endogenous purinergic effects, mediated by P2X receptors, on cholinergic neurons. Our study provides evidence for a role of cannabinoids in the modulation of interneuronal purinergic transmission.

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.

Cannabinoid CB(1) receptor activation modulates spontaneous contractile activity in mouse ileal longitudinal muscle

The purpose of the present study was to examine whether cannabinoid receptor agonists influence spontaneous contractile activity of longitudinal muscle in mouse ileum in vitro. Isolated segments of mouse ileum displayed spontaneous contractions with an amplitude and frequency of about 300 mg and 30 cpm, respectively. The endocannabinoid anandamide (1-100 microM), the selective cannabinoid CB(1) receptor agonist, ACEA (0.1 microM-10 microM), but not the selective cannabinoid CB(2) receptor agonist, JWH 133 (0.1 microM-10 microM), reduced in a concentration-dependent manner the spontaneous mechanical activity. The inhibitory effect consisted in a decrease of the mean amplitude of longitudinal spontaneous contractions, without changes in the resting tone. The inhibitory effect induced by cannabinoids was significantly antagonized by the selective cannabinoid CB(1) receptor antagonist, SR141716A (0.1 microM), but not by the selective cannabinoid CB(2) receptor antagonist, AM630 (0.1 microM). None of the cannabinoid antagonists, at the concentration used, did affect the spontaneous mechanical activity. The ACEA-induced reduction of spontaneous contractions was almost abolished by tetrodotoxin, atropine or apamin and it was unaffected by hexamethonium or N(omega)-nitro-l-arginine methyl ester (l-NAME), inhibitor of nitric oxide synthase. The myogenic contractions evoked by carbachol were not affected by ACEA. In conclusion, the present results suggest that activation of neural cannabinoid CB(1) receptors may play a role in the control of spontaneous mechanical activity through inhibition of acetylcholine release from cholinergic nerve. Activation of small conductance Ca(2+)-dependent K(+) channels is involved in this action.

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.

Effects of a cannabinoid receptor agonist on colonic motor and sensory functions in humans: a randomized, placebo-controlled study

Cannabinoid receptors (CBR) are located on cholinergic neurons in the brain stem, stomach, and colon. CBR stimulation inhibits motility in rodents. Effects in humans are unclear. Dronabinol (DRO), a nonselective CBR agonist, inhibits colonic motility and sensation. The aim of this study was to compare effects of DRO and placebo (PLA) on colonic motility and sensation in healthy volunteers. Fifty-two volunteers were randomly assigned (double-blind) to a single dose of 7.5 mg DRO or PLA postoperative with concealed allocation. A balloon-manometric assembly placed into the descending colon allowed assessment of colonic compliance, motility, tone, and sensation before and 1 h after oral ingestion of medication, and during fasting, and for 1 h after 1,000-kcal meal. There was an overall significant increase in colonic compliance (P = 0.045), a borderline effect of relaxation in fasting colonic tone (P = 0.096), inhibition of postprandial colonic tone (P = 0.048), and inhibition of fasting and postprandial phasic pressure (P = 0.008 and 0.030, respectively). While DRO did not significantly alter thresholds for first gas or pain sensation, there was an increase in sensory rating for pain during random phasic distensions at all pressures tested and in both genders (P = 0.024). In conclusion, in humans the nonselective CBR agonist, DRO, relaxes the colon and reduces postprandial colonic motility and tone. Increase in sensation ratings to distension in the presence of relaxation of the colon suggests central modulation of perception. The potential for CBR to modulate colonic motor function in diarrheal disease such as irritable bowel syndrome deserves further study.

Involvement of CB1 and CB2 receptors in the modulation of cholinergic neurotransmission in mouse gastric preparations

While most of the studies concerning the role of cannabinoids on gastric motility have focused the attention on the gastric emptying in in vivo animal models, there is little information about the cannabinoid peripheral influence in the stomach. In addition, the functional features of CB2 receptors in the gastrointestinal tract have been poorly characterized. The purpose of the present study was to investigate the effects of cannabinoid drugs on the excitatory cholinergic and inhibitory non-adrenergic non-cholinergic (NANC) neurotransmission in mouse isolated gastric preparations. Intraluminal pressure from isolated whole stomach was recorded and mechanical responses induced by electrical field stimulation (EFS) were analyzed in different experimental conditions. EFS (0.5ms duration, supramaximal voltage, in trains of 5s, 2-16Hz) caused a cholinergic contraction, which was abolished by atropine or tetrodotoxin (TTX). The cannabinoid receptor agonist, WIN 55,212-2, the endogenous ligand, anandamide, the selective CB1 receptor agonist ACEA, and the selective CB2 receptor agonists, JWH015 and JWH133, produced a concentration-dependent reduction of the EFS-evoked cholinergic contractions. SR141716A, CB1 receptor antagonist, significantly attenuated the inhibitory effects induced by WIN 55,212-2, anandamide or ACEA, without affecting those caused by JWH133. AM630, CB2 receptor antagonist, reduced the inhibitory effects induced by WIN 55,212-2, anandamide, JWH015 or JWH133, without affecting those caused by ACEA. The joint application of SR141716A and AM630 was able of fully preventing the WIN 55,212-2 and anandamide actions. The cannabinoid antagonists failed per se to affect the neurally evoked responses. Cannabinoids did not modify the contractions produced by exogenous carbachol. In the presence of atropine and guanethidine (NANC conditions) EFS-induced TTX-sensitive relaxation consisting in an early and rapid component followed by a second slow phase, which were unaffected by cannabinoid drugs. In conclusion, the present results suggest that cannabinoids play a prejunctional modulatory role on the cholinergic excitatory transmission without affecting the NANC inhibitory transmission. In addition, this study provides experimental evidence that also the activation of CB2 receptors is able to reduce cholinergic neurotransmission in the mouse stomach.

Tolerance to cannabinoid response on the myenteric plexus of guinea-pig ileum and human small intestinal strips

1. We studied tolerance to cannabinoid agonist action by comparing the in vitro inhibition of electrically evoked contractions of longitudinal muscle from small intestine of human and guinea-pig (myenteric plexus preparations) after 48-h incubation with the synthetic agonist (+) WIN 55,212-2. We also investigated the intrinsic response to the selective cannabinoid CB(1) receptor antagonist rimonabant in control and tolerant strips. 2. (+) WIN 55,212-2 inhibited guinea-pig (IC(50) 4.8 nM) and human small intestine (56 nM) contractions with similar potency before or after 48-h incubation in drug-free conditions; this effect was competitively antagonized by rimonabant (pA(2), 8.4, 8.2). A 48-h preincubation with (+) WIN 55,212-2, but not with (-) WIN 55,212-3, completely abolished the acute agonist response in both tissue preparations. The opiate K-receptor agonist U69593 inhibited human small intestine contractions with a similar potency in control and strips tolerant to (+) WIN 55,212-2, IC(50) 39 and 43 nM. 3. Unlike human tissue, in guinea-pig small intestine, which has a high level of endocannabinoids, rimonabant alone increased the twitches induced by the electrical field stimulation (EC(50) 100 nM) with a maximal effect of 123%. 4. In strips tolerant to (+) WIN 55,212-2, rimonabant markedly increased (155%) the electrical twitches in human ileum and in guinea-pig myenteric plexus smooth muscle (133%). 5. This study shows tolerance can be induced to the cannabinoids' action in intestinal strips of human and guinea-pig by long in vitro incubation with the agonist (+) WIN 55,212-2.

Investigation on the relationship between cannabinoid CB1 and opioid receptors in gastrointestinal motility in mice

1. This study investigated whether (a) cannabinoid CB(1) receptor knockout (CB(1)(-/-)) mice displayed altered gastrointestinal transit and (b) cannabinoid CB(1) and opioid receptors functionally interact in the regulation of gastrointestinal transit. 2. Gastrointestinal transit was assessed by the Whole Gastrointestinal Transit, measuring the excretion time of an intragastrically administered marker (whole intestine), and the Upper Gastrointestinal Transit, measuring the distance covered by the marker in the small intestine. 3. CB(1)(-/-) and homozygous CB(1)(+/+) (CB(1)(+/+)) mice did not differ in both whole gut and small intestine transit. CB(1)(-/-) and CB(1)(+/+) mice were equally responsive to the inhibitory effect of morphine (10 mg kg(-1)) and loperamide (3 mg kg(-1)) on whole gut transit.4. Additionally, in CD1 mice the cannabinoid CB(1) receptor antagonist, rimonabant (0-0.5 mg kg(-1)), failed to block the inhibitory effect of morphine (0-1.25 mg kg(-1)) and loperamide (0-0.5 mg kg(-1)) on transit in small and whole intestine. Similarly, the opioid receptor antagonists, naloxone (0-1 mg kg(-1)) and naltrexone (0-10 mg kg(-1)), failed to block the inhibitory effect of the cannabinoid WIN 55,212-2 (0-3 mg kg(-1)) on transit in small and whole intestine.5. These results suggest that (a) compensatory mechanisms likely developed in CB(1)(-/-) mice to overcome the lack of inhibitory function of endocannabinoid system; (b) cannabinoid and opioid receptor systems did not interact in regulating gastrointestinal transit in mice.

Vanilloid VR1 receptor is involved in rimonabant-induced neuroprotection

Recently, a potential neuroprotective effect of rimonabant, independent of the CB1 receptor interaction, has been proposed. In the present study, the role of transient receptor potential channel vanilloid subfamily member 1, named VR1, on neuroprotective effect of rimonabant, on global cerebral ischemia in gerbils, was investigated. Rimonabant (0.05-3 mg kg-1), given i.p. 5 min after recirculation, dose dependently antagonized the ischemia-induced decrease in electroencephalographic (EEG) total spectral power and restored relative frequency band distribution 7 days after ischemia. Rimonabant (0.125-0.5 mg kg-1) fully prevented ischemia-induced hyperlocomotion 1 day after ischemia and memory impairment evaluated in a passive avoidance task, 3 days after ischemia. At 7 days after ischemia, the survival of pyramidal cells, in the CA1 subfield, was respectively 91 and 96%, in the animals given rimonabant 0.25 and 0.5 mg kg-1, compared to the vehicle group. Higher doses were not protective. The protection induced by rimonabant followed a bell-shaped curve, the maximal active doses being 0.25 and 0.5 mg kg-1. Capsazepine (0.01 mg kg-1), a selective VR1 vanilloid receptor antagonist, completely reversed rimonabant-induced neuroprotective effects against EEG flattening, memory impairment and CA1 hippocampal neuronal loss. These findings suggest that VR1 vanilloid receptors are involved in rimonabant's neuroprotection even if other mechanisms can contribute to this effect.

Effects of castration on cannabinoid cb receptor expression and on the biological actions of cannabinoid in the parotid gland

In the present study, we examined whether cannabinoid receptor expression and the effects of receptor stimulation vary as a function of gonadal status in a peripheral tissue, namely the male rat parotid gland. Four groups of male rats were studied: gonadal intact, castrated, castrated testosterone (1 mg/100 g bodyweight) treated and gonadal intact testosterone treated. 2. The results showed that the density of CB(1) receptors decreased after castration and that receptor density was restored to control values after testosterone treatment. This decrement was associated with a decrease of anandamide (10(-10) to 10(-5) mol/L)-induced cAMP accumulation and amylase release without changes in the anandamide-induced inhibition of Na(+)/K(+)-ATPase activity. 3. Castration did not modify either the subtype of cannabinoid receptor involved in the actions of anandamide or drug affinity for the receptor. 4. The mechanism underlying anandamide-induced cAMP accumulation, amylase release and inhibition of Na(+)/K(+)-ATPase activity, namely through the activation of adenylyl cyclase, was the same in control and castrated rats. 5. Basal cAMP accumulation, amylase release and Na(+)/K(+)-ATPase activity were not altered by castration. 6. Castration had no effect on the concentration of total protein. 7. It can be concluded that CB(1) cannabinoid receptor expression is regulated by testosterone in male rat parotid gland and this has functional implications for cAMP accumulation and amylase release.

Fatty acid amide hydrolase controls mouse intestinal motility in vivo

BACKGROUND & AIMS

Fatty acid amide hydrolase (FAAH) catalyzes the hydrolysis both of the endocannabinoids (which are known to inhibit intestinal motility) and other bioactive amides (palmitoylethanolamide, oleamide, and oleoylethanolamide), which might affect intestinal motility. The physiologic role of FAAH in the gut is largely unexplored. In the present study, we evaluated the possible role of FAAH in regulating intestinal motility in mice in vivo.

METHODS

Motility was measured by evaluating the distribution of a fluorescent marker along the small intestine; FAAH messenger RNA (mRNA) levels were analyzed by reverse-transcription polymerase chain reaction (RT-PCR); endocannabinoid levels were measured by isotope-dilution, liquid chromatography, mass spectrometry.

RESULTS

Motility was inhibited by N-arachidonoylserotonin (AA-5-HT) and palmitoylisopropylamide, 2 selective FAAH inhibitors, as well as by the FAAH substrates palmitoylethanolamide, oleamide, and oleoylethanolamide. The effect of AA-5-HT was reduced by the CB1 receptor antagonist rimonabant and by CB1 deficiency in mice but not by the vanilloid receptor antagonist 5'-iodoresiniferatoxin. In FAAH-deficient mice, pharmacologic blockade of FAAH did not affect intestinal motility. FAAH mRNA was detected in different regions of the intestinal tract.

CONCLUSIONS

We conclude that FAAH is a physiologic regulator of intestinal motility and a potential target for the development of drugs capable of reducing intestinal motility.

Evaluation of the effect of age on cannabinoid receptor functionality and expression in guinea-pig ileum longitudinal muscle–myenteric plexus preparations

Cannabinoid drugs exert a wide range of biological effects and are currently under study for their multiple potential therapeutic uses. Cannabinoids reduce gastrointestinal (GI) motility and this is mediated by the CB1 cannabinoid receptor (CB1R) present in the myenteric neurones. GI motility can also be affected by a variety of pathophysiological situations, including ageing. The purpose of this work was to study the influence of age on the functionality and expression of CB1R in the myenteric plexus. Ileal longitudinal muscle-myenteric plexus (LMMP) preparations from young, adult and old guinea-pigs were used in two sets of experiments: in vitro assessment of the inhibitory cannabinoid effect upon electrically stimulated contractions and immunohistochemical quantification of myenteric neurones expressing CB1R. LMMP preparations responded to the synthetic cannabinoid WIN 55,212-2, and the endogenous cannabinoid ligand anandamide in an age-independent manner. The total number of CB1R-immunoreactive (IR) myenteric neurones, which included at least part of the motor neurones to the longitudinal smooth muscle, decreased in proportion to the general neuronal population; however, the proportion of CB1R-IR neurones was preserved in old animals. These data may justify the preservation of the effectiveness of the cannabinoids in the isolated guinea-pig ileum. This age-related independency of CB1R expression and effect on GI motility could be of interest if cannabinoids are to be used therapeutically.

Peripheral, but not central effects of cannabidiol derivatives: mediation by CB(1) and unidentified receptors

Delta-9 tetrahydrocannabinol (Delta(9)-THC) and (-)-cannabidiol ((-)-CBD) are major constituents of the Cannabis sativa plant with different pharmacological profiles: (Delta(9)-THC activates cannabinoid CB(1) and CB(2) receptors and induces psychoactive and peripheral effects. (-)-CBD possesses no, or very weak affinity for these receptors. We tested a series of (+)- and (-)-CBD derivatives for central and peripheral effects in mice. None of the (-)-CBD derivatives were centrally active, yet most inhibited intestinal motility. Of the five (+)-CBD derivatives, all with CB(1) receptor affinity, only (+)-7-OH-CBD-DMH (DMH=1,1-dimethylheptyl), acted centrally, while all five arrested defecation. The effects of (+)-CBD-DMH and (+)-7-OH-CBD-DMH were inhibited by the CB(1) receptor antagonist SR141716. The CB(2) receptor antagonist SR144528, and the vanilloid TRPV1 receptor antagonist capsazepine, had no influence. Further, the (-)-CBD derivatives (-)-7-COOH-CBD and (-)-7-COOH-CBD-DMH, displayed antiinflammatory activity. We suggest that (+)-CBD analogues have mixed agonist/antagonist activity in the brain. Second, (-)-CBD analogues which are devoid of cannabinoid receptor affinity but which inhibit intestinal motility, suggest the existence of a non-CB(1), non-CB(2) receptor. Therefore, such analogues should be further developed as antidiarrheal and/or antiinflammatory drugs. We propose to study the therapeutic potential of (-)- and (+)-CBD derivatives for complex conditions such as inflammatory bowel disease and cystic fibrosis.

Cannabinoids and the digestive tract

In the digestive tract there is evidence for the presence of high levels of endocannabinoids (anandamide and 2-arachidonoylglycerol) and enzymes involved in the synthesis and metabolism of endocannabinoids. Immunohistochemical studies have shown the presence of CB1 receptors on myenteric and submucosal nerve plexuses along the alimentary tract. Pharmacological studies have shown that activation of CB1 receptors produces relaxation of the lower oesophageal sphincter, inhibition of gastric motility and acid secretion, as well as intestinal motility and secretion. In general, CB1-induced inhibition of intestinal motility and secretion is due to reduced acetylcholine release from enteric nerves. Conversely, endocannabinoids stimulate intestinal primary sensory neurons via the vanilloid VR1 receptor, resulting in enteritis and enhanced motility. The endogenous cannabinoid system has been found to be involved in the physiological control of colonic motility and in some pathophysiological states, including paralytic ileus, intestinal inflammation and cholera toxin-induced diarrhoea. Cannabinoids also possess antiemetic effects mediated by activation of central and peripheral CB1 receptors. Pharmacological modulation of the endogenous cannabinoid system could provide a new therapeutic target for the treatment of a number of gastrointestinal diseases, including nausea and vomiting, gastric ulcers, secretory diarrhoea, paralytic ileus, inflammatory bowel disease, colon cancer and gastro-oesophageal reflux conditions.

Inverse agonism and neutral antagonism at cannabinoid CB1 receptors

There are at least two types of cannabinoid receptor, CB1 and CB2, both G protein coupled. CB1 receptors are expressed predominantly at nerve terminals and mediate inhibition of transmitter release whereas CB2 receptors are found mainly on immune cells, one of their roles being to modulate cytokine release. Endogenous cannabinoid receptor agonists also exist and these "endocannabinoids" together with their receptors constitute the "endocannabinoid system". These discoveries were followed by the development of a number of CB1- and CB2-selective antagonists that in some CB1 or CB2 receptor-containing systems also produce "inverse cannabimimetic effects", effects opposite in direction from those produced by cannabinoid receptor agonists. This review focuses on the CB1-selective antagonists, SR141716A, AM251, AM281 and LY320135, and discusses possible mechanisms by which these ligands produce their inverse effects: (1) competitive surmountable antagonism at CB1 receptors of endogenously released endocannabinoids, (2) inverse agonism resulting from negative, possibly allosteric, modulation of the constitutive activity of CB1 receptors in which CB1 receptors are shifted from a constitutively active "on" state to one or more constitutively inactive "off" states and (3) CB1 receptor-independent mechanisms, for example antagonism of endogenously released adenosine at A1 receptors. Recently developed neutral competitive CB1 receptor antagonists, which are expected to produce inverse effects through antagonism of endogenously released endocannabinoids but not by modulating CB1 receptor constitutive activity, are also discussed. So too are possible clinical consequences of the production of inverse cannabimimetic effects, there being convincing evidence that released endocannabinoids can have "autoprotective" roles.

(+)-Cannabidiol analogues which bind cannabinoid receptors but exert peripheral activity only

Delta9-Tetrahydrocannabinol (Delta9-THC) and (-)-cannabidiol are major constituents of the Cannabis sativa plant with different pharmacological profiles: (-)-Delta9-tetrahydrocannabinol, but not (-)-cannabidiol, activates cannabinoid CB1 and CB2 receptors and induces psychoactive and peripheral effects. We have tested a series of (+)-cannabidiol derivatives, namely, (+)-cannabidiol-DMH (DMH-1,1-dimethylheptyl-), (+)-7-OH-cannabidiol-DMH, (+)-7-OH- cannabidiol, (+)-7-COOH- cannabidiol and (+)-7-COOH-cannabidiol-DMH, for central and peripheral (intestinal, antiinflammatory and peripheral pain) effects in mice. Although all (+)-cannabidiols bind to cannabinoid CB1 and CB2 receptors, only (+)-7-OH-cannabidiol-DMH was centrally active, while all (+)-cannabidiol analogues completely arrested defecation. The effects of (+)-cannabidiol-DMH and (+)-7-OH-cannabidiol-DMH were partially antagonized by the cannabinoid CB1 receptor antagonist N-(piperidiny-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716), but not by the cannabinoid CB2 receptor antagonist N-[-(1S)-endo-1,3,3-trimethil bicyclo [2.2.1] heptan-2-yl-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528), and had no effect on CB1(-/-) receptor knockout mice. (+)-Cannabidiol-DMH inhibited the peripheral pain response and arachidonic-acid-induced inflammation of the ear. We conclude that centrally inactive (+)-cannabidiol analogues should be further developed as antidiarrheal, antiinflammatory and analgesic drugs for gastrointestinal and other peripheral conditions.

Evidence for differential modulation of conditioned aversion and fear-conditioned analgesia by CB1 receptors

Fear-conditioned analgesia is an important survival response mediated by substrates controlling nociception and aversion. Cannabinoid(1) (CB(1)) receptors play an important role in nociception and aversion. However, their role in fear-conditioned analgesia has not been investigated. This study investigated the effects of systemic administration of the CB(1) receptor antagonist, SR141716A (1 mg/kg, i.p.), on fear-conditioned analgesia and conditioned aversion in rats. Twenty-four hours after receiving footshock, rats exhibited reduced formalin-evoked nociceptive behaviour, increased freezing and increased defecation when tested in the footshock apparatus, compared with non-footshocked formalin-injected rats. SR141716A attenuated fear-conditioned analgesia, freezing and defecation. Importantly, SR141716A had no effect on formalin-evoked nociceptive behaviour over an equivalent time period in rats not receiving footshock. SR141716A had no effect on contextually induced freezing during the first half of the test trial in rats receiving intra-plantar injection of saline. Administration of SR1417176A did, however, attenuate short-term extinction of contextually induced freezing and ultrasound emission in rats receiving intra-plantar saline, compared with vehicle-treated saline controls. These data suggest an important role for the CB(1) receptor in mediating fear-conditioned analgesia and provide evidence for differential modulation of conditioned aversive behaviour by CB(1) receptors during tonic, persistent pain.

Effects of cannabinoid receptor-2 activation on accelerated gastrointestinal transit in lipopolysaccharide-treated rats

The biological effects of cannabinoids (CB) are mediated by CB(1) and CB(2) receptors. The role of CB(2) receptors in the gastrointestinal tract is uncertain. In this study, we examined whether CB(2) receptor activation is involved in the regulation of gastrointestinal transit in rats. Basal and lipopolysaccharide (LPS)-stimulated gastrointestinal transit was measured after instillation of an Evans blue-gum Arabic suspension into the stomach, in the presence of specific CB(1) and CB(2) agonists and antagonists, or after treatment with inhibitors of mediators implicated in the transit process. In control rats a CB(1) (ACEA; 1 mg kg(-1)), but not a CB(2) (JWH-133; 1 mg kg(-1)), receptor agonist inhibited basal gastrointestinal transit. The effects of the CB(1) agonist were reversed by the CB(1) antagonist AM-251, which alone increased basal transit. LPS treatment increased gastrointestinal transit. This increased transit was reduced to control values by the CB(2), but not the CB(1), agonist. This inhibition by the CB(2) agonist was dose dependent and prevented by a selective CB(2) antagonist (AM-630; 1 mg kg(-1)). By evaluating the inhibition of LPS-enhanced gastrointestinal transit by different antagonists, the effects of the CB(2) agonist (JWH-133; 1 mg kg(-1)) were found to act via cyclooxygenase, and to act independently of inducible nitric oxide synthase (NOS) and platelet-activating factor. Interleukin-1 beta and constitutive NOS isoforms may be involved in the accelerated LPS transit. The activation of CB(2) receptors in response to LPS is a mechanism for the re-establishment of normal gastrointestinal transit after an inflammatory stimulus.

Rapid tolerance to the intestinal prokinetic effect of cannabinoid CB1 receptor antagonist, SR 141716 (Rimonabant)

The cannabinoid CB(1) receptor antagonist, SR 141716 (Rimonabant), has been reported to stimulate, when acutely administered, intestinal motility in mice. The present study was aimed at determining whether tolerance develops to its repeated administration. Mice were treated twice a day for up to 8 consecutive days with 0, 3 and 5.6 mg/kg SR 141716 (i.p.). On days 1, 3, 5 and 8, separate groups of mice were treated intragastrically with a non-absorbable colored marker (carmine). The distance traveled by the head of the marker in the small intestine was recorded. On day 1, SR 141716 markedly activated intestinal peristalsis, but complete tolerance to this effect developed within the third day of treatment. The results may have some relevance to the proposed future clinical use of SR 141716.

Role of cannabinoid CB1 receptors and tumor necrosis factor-alpha in the gut and systemic anti-inflammatory activity of SR 141716 (rimonabant) in rodents

(1) We investigated the effect of the cannabinoid CB1 receptor antagonist, SR 141716, on indomethacin-induced small intestine inflammation and Escherichia coli lipopolysaccharide (LPS)-induced plasma TNF-alpha (TNF) release in comparison to the cannabinoid CB2 receptor antagonist, SR 144528, in rodents. (2) In rats, indomethacin induced significant ulcer formation in the small intestine; this was accompanied by an increase in tissue TNF levels and myeloperoxidase (MPO) activity. SR 141716 prevented the ulcers and the rise in TNF levels (ID50 3.3, 0.4 mg kg-1, respectively) and MPO activity. SR 144528 prevented intestinal ulcers only. (3) The effect of SR 141716 against indomethacin-induced ulcers and increase of plasma TNF levels after LPS was also studied in wild-type and CB1 receptor knockout mice. Indomethacin induced intestinal ulcers in mice, but not tissue TNF production and MPO activity. SR 141716 reduced the ulcers to a similar extent in wild-type and CB1 receptor knockout mice. In rats and wild-type mice, but not in CB1 receptor knockout mice, SR 141716 inhibited the LPS-induced increase in plasma TNF levels. (4) These findings provide evidence that the indomethacin model of intestinal lesions differs in rat and mouse and support the existence of several mechanisms for the antiulcer activity of SR141716, the most important involving the inhibition of TNF production. The potent anti-inflammatory activity of SR141716 in rodents indicated its potential therapeutic interest in chronic immune-inflammatory diseases.

An endogenous cannabinoid tone attenuates cholera toxin-induced fluid accumulation in mice

BACKGROUND & AIMS

Cholera toxin (CT) is the most recognizable enterotoxin causing secretory diarrhea, a major cause of infant morbidity and mortality throughout the world. In this study, we investigated the role of the endogenous cannabinoid system (i.e., the cannabinoid receptors and their endogenous ligands) in CT-induced fluid accumulation in the mouse small intestine.

METHODS

Fluid accumulation was evaluated by enteropooling; endocannabinoid levels were measured by isotope-dilution gas chromatography mass spectrometry; CB(1) receptors were localized by immunohistochemistry and their messenger RNA (mRNA) levels were quantified by reverse-transcription polymerase chain reaction (PCR).

RESULTS

Oral administration of CT to mice resulted in an increase in fluid accumulation in the small intestine and in increased levels of the endogenous cannabinoid, anandamide, and increased expression of the cannabinoid CB(1) receptor mRNA. The cannabinoid receptor agonist CP55,940 and the selective cannabinoid CB(1) receptor agonist arachidonoyl-chloro-ethanolamide inhibited CT-induced fluid accumulation, and this effect was counteracted by the CB(1) receptor antagonist SR141716A, but not by the CB(2) receptor antagonist SR144528. SR141716A, per se, but not the vanilloid VR1 receptor antagonist capsazepine, enhanced fluid accumulation induced by CT, whereas the selective inhibitor of anandamide cellular uptake, VDM11, prevented CT-induced fluid accumulation.

CONCLUSIONS

These results indicate that CT, along with enhanced intestinal secretion, causes overstimulation of endocannabinoid signaling with an antisecretory role in the small intestine.

Behaviorally active doses of the CB1 receptor antagonist SR 141716A increase brain serotonin and dopamine levels and turnover

Large doses (10-40 mg/kg) of the selective cannabinoid CB(1) receptor antagonist, SR 141716A, produce the head-twitch response (HTR) and scratching in rodents and vomiting in the least shrew (Cryptotis parva). Agents that increase brain serotonin (5-HT) levels induce the HTR in rodents, whereas enhancements in either brain 5-HT or dopamine concentrations can lead to production of emesis in vomiting species. The present study was undertaken to demonstrate whether large doses of SR 141716A can (1) induce the HTR and scratching in the least shrew and (2) cause concurrent biochemical changes in brain 5-HT and dopamine concentrations. SR 141716A (0, 1, 5, 10, 20 and 40 mg/kg i.p.) administration induced the HTR, scratching and vomiting. The HTR effect was bell shaped with a maximum frequency occurring at the 20 mg/kg SR 141716A dose, whereas the scratching and vomiting behaviors displayed dose-dependent effects. The selective 5-HT(2A/C) receptor antagonist, SR 46349B (0, 0.1, 0.25, 1, 3 and 6 mg/kg i.p.), differentially attenuated all SR 141716A (20 mg/kg)-induced behaviors because the HTR was relatively more potently and completely blocked. In the shrew forebrain, SR 141716A (20 and 40 mg/kg ip) caused dose- and time-dependent increases in the levels of 5-HT and dopamine and the concentrations of their major metabolites [5-hydroxyindole acetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA)] and the turnover of both monoamines. Although the effects of SR 141716A on brainstem concentrations of both monoamines and their metabolites were not always consistent, the CB(1) antagonist did increase the turnover of both 5-HT and dopamine. The present findings suggest that the mechanism and the neurochemical substrate for SR 141716A-induced HTR and scratching behaviors is enhancement of 5-HT release, whereas increased release of 5-HT and dopamine probably contributes to the production of emesis.

Kinin-induced anion-dependent secretion in porcine ileum: characterization and involvement of opioid- and cannabinoid-sensitive enteric neural circuits

The intestinal secretory actions of the proinflammatory peptide kallidin (lysyl-bradykinin) are mediated partially by enteric neurons. We hypothesized that kallidin produces neurogenic anion secretion through opioid- and cannabinoid-sensitive enteric neural pathways. Changes in short-circuit current (I(sc)) across sheets of porcine ileal mucosa-submucosa mounted in Ussing chambers were measured in response to kallidin (1 microM) or drugs added to the contraluminal bathing medium. Kallidin transiently increased I(sc), an effect reduced after inhibition of neuronal conduction by 0.1 microM saxitoxin, cyclooxygenase inhibition by 10 microM indomethacin, or kinin B(2) receptor blockade by 1 microM d-arginyl-l-arginyl-l-prolyl-trans-4-hydroxy-l-prolylglycyl-3-(2-thienyl)-l-alanyl-l-seryl-d-1,2,3,4-tetrahydro-3-isoquinolinecarbonyl-l-(2alpha,3beta,7alphabeta)-octahydro-1H-indole-2-carbonyl-l-arginine (HOE-140). Its action was dependent upon extracellular Cl(-) or HCO(3)(-) ions, but was resistant to 10 microM bumetanide or 0.3 mM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, and seemed to involve luminal alkalinization as measured by pH-stat titration. Kallidin-induced I(sc) elevations were sensitive to saxitoxin in tissues bathed in Cl(-)-, but not HCO(3)(-)-deficient media. Tissues pretreated with 0.1 microM [d-Pen(2,5)]-enkephalin, a selective delta-opioid agonist, displayed reduced I(sc) responses to kallidin; this effect was prevented by the delta-opioid antagonist naltrindole. At a contraluminal concentration of 1 microM, the cannabinoid receptor agonist (6aR)-trans-3-(1,1-dimethylheptyl)-6a,7,10,10a-tetrahydro-1-hydroxy-6,6-dimethyl-6H-dibenzo[b,d]pyran-9-methanol (HU-210) also attenuated responses to kallidin. Proinflammatory kinins seem to stimulate neurogenic anion secretion in porcine ileum by activating enteric neural circuits expressing inhibitory opioid and possibly cannabinoid receptors.

Cannabinoids for gastrointestinal diseases: potential therapeutic applications

Delta(9)-Tetrahydrocannabinol (the active ingredient of marijuana), as well as endogenous and synthetic cannabinoids, exert many biological functions by activating two types of cannabinoid receptors, CB(1) and CB(2) receptors. CB(1) receptors have been detected on enteric nerves, and pharmacological effects of their activation include gastroprotection, reduction of gastric and intestinal motility and reduction of intestinal secretion. The digestive tract also contains endogenous cannabinoids (i.e., the endocannabinoids anandamide and 2-aracidonylglycerol) and mechanisms for endocannabinoid inactivation (i.e., endocannabinoids uptake and enzymatic degradation). Cannabinoid receptors, endocannabinoids and the proteins involved in endocannabinoids inactivation are collectively referred as the 'endogenous cannabinoid system'. A pharmacological modulation of the endogenous cannabinoid system could provide new therapeutics for the treatment of a number of gastrointestinal diseases, including nausea and vomiting, gastric ulcers, irritable bowel syndrome, Crohn's disease, secretory diarrhoea, paralytic ileus and gastroesophageal reflux disease. Some cannabinoids are already in use clinically, for example, nabilone and delta(9)-tetrahydrocannabinol are used as antiemetics.

Modulation of gastric emptying and gastrointestinal transit in rats through intestinal cannabinoid CB(1) receptors

We studied the delay in gastric emptying and gastrointestinal transit induced by the cannabinoid receptor agonists (+)-WIN 55,212-2 (R(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazin-yl]-(1-naphthalenyl)methanone mesylate) and CP 55,940 ((-)-cis-3[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl) cyclohexanol), as prevented by the selective cannabinoid CB(1)-receptor antagonist SR141716 ((N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide)) in rats after systemic or central drug administration. Oral SR141716 showed comparable potency (ID(50) range 1.0-3.9 mg/kg) in antagonizing gastric emptying and gastrointestinal transit delay by (+)-WIN 55,212-2 or CP 55,940. Gastric emptying and gastrointestinal transit delay after intracerebroventricular (i.c.v.) (+)-WIN 55,212-2 was prevented by oral or i.c.v. SR141716, but i.c.v. SR141716 did not significantly reduce the effect of i.p. (+)-WIN 55,212-2. Pertussis toxin prevented the delaying action of i.c.v. (+)-WIN 55,212-2 on both gastric emptying and gastrointestinal transit, but had no effect on (+)-WIN 55,212-2 i.p. These findings are consistent with a primary role of peripheral cannabinoid CB(1) receptor mechanisms in gastrointestinal transit delay by specific agonists.

Localisation of cannabinoid CB(1) receptor immunoreactivity in the guinea pig and rat myenteric plexus

Activation of cannabinoid CB(1) receptors inhibits gastrointestinal motility, propulsion, and transit, whereas selective antagonism of these receptors has the opposite effects, suggesting the presence of endocannabinoid tone. Supporting evidence for presynaptic CB(1) receptors on myenteric neurons has been found in vitro. In this study, selective CB(1) receptor antibodies and neuronal markers were used to identify and characterise myenteric neurons expressing cannabinoid receptors. Whole mounts of rat and guinea pig myenteric preparations were dually labelled with antibodies against the CB(1) receptor and choline acetyltransferase, neurofilament proteins, calbindin, calretinin, synapsin I, microtubule-associated protein-2, calcitonin gene-related peptide, or substance P. The pattern of CB(1) receptor labelling and the neurochemical classification of CB(1) receptor-positive cells were markedly influenced by the species and fixation procedure. Virtually all choline acetyltransferase-immunoreactive myenteric neurons expressed CB(1) receptors in ganglia from both species. Subpopulations of neurons identified with calbindin, calretinin, and microtubule-associated protein-2 did not express CB(1) receptors. A few calcitonin gene-related peptide- and substance P-positive somata coexpressed CB(1) receptor immunoreactivity but showed little colocalisation on individual fibres. There was a close association between CB(1) receptor immunoreactivity and fibres labelled for synaptic protein, suggesting a role in the modulation of transmitter release. Functional responses to cannabinoids in the presence of hexamethonium suggest further that CB(1) receptors occur on excitatory motoneurons. In conclusion, CB(1) receptors are expressed on a variety of cholinergic sensory, interneuronal, and motor neurons in myenteric ganglia.

Endocannabinoids as physiological regulators of colonic propulsion in mice

BACKGROUND & AIMS

Activation of enteric cannabinoid CB1 receptors inhibits motility in the small intestine; however, it is not known whether endogenous cannabinoids (anandamide and 2-arachidonylglycerol) play a physiologic role in regulating intestinal motility. In the present study, we investigated the possible involvement of endocannabinoids in regulating intestinal propulsion in the mouse colon in vivo.

METHODS

Intestinal motility was studied measuring the expulsion of a glass bead inserted into the distal colon; endocannabinoid levels were measured by isotope-dilution gas chromatography-mass spectrometry; anandamide amidohydrolase activity was measured by specific enzyme assays. CB1 receptors were localized by immunohistochemistry.

RESULTS

Anandamide, WIN 55,212-2, cannabinol (nonselective cannabinoid agonists), and ACEA (a selective CB1 agonist) inhibited colonic propulsion; this effect was counteracted by SR141716A, a CB1 receptor antagonist. Administered alone, SR141716A increased motility, whereas the inhibitor of anandamide cellular reuptake, VDM11, decreased motility. High amounts of 2-arachidonylglycerol and particularly anandamide were found in the colon, together with a high activity of anandamide amidohydrolase. CB1 receptor immunoreactivity was colocalized to a subpopulation of choline acetyltransferase-immunoreactive neurons and fiber bundles in the myenteric plexus.

CONCLUSIONS

We conclude that endocannabinoids acting on myenteric CB1 receptors tonically inhibit colonic propulsion in mice.

Functional assessment of neuronal cannabinoid receptors in the muscular layers of human ileum and colon

BACKGROUND & AIMS

The notion that specific receptors account for the ability of natural and synthetic cannabinoids to alter physiological functions, prompted this study aimed at assessing their functional presence in the human gut.

METHODS

The effects have been studied of cannabinoids and selective antagonists of their receptors on chemically or electrically evoked contractions in preparations of human intestinal smooth muscle in vitro.

RESULTS

Atropine prevented the contractions of longitudinal and circular muscle strips of ileum and colon induced by carbachol or electrical field stimulation; tetrodotoxin abolished only the latter which suggests they do involve activation of cholinergic neurons. The synthetic cannabinoid (+)WIN 55,212-2 had no effect on carbachol contractions, but in a concentration-dependent fashion prevented those elicited by electrical field stimulation - which were insensitive to the putative endogenous cannabinoid anandamide - more potently in longitudinal than in circular strips. The selective CB1 receptor antagonist SR141716, which had no effect in the absence of (+)WIN 55,212-2, competitively antagonised its inhibition of electrical field stimulation contractions, unlike the selective CB2 antagonist SR144528.

CONCLUSIONS

Cannabinoid CB1 receptors are functionally present in the human ileum and colon; their pharmacological activation apparently results in inhibition of excitatory cholinergic pathways subserving smooth muscle contraction.