Dietary capsaicin-mediated attenuation of hypertension in a rat model of renovascular hypertension.

Background: Capsaicin, a pungent component of chili pepper, has been reported to decrease blood pressure (BP) and to cause vasorelaxation via nitric oxide (NO) production. However, it is still unclear how dietary capsaicin effects on renovascular hypertension. To examine this, we observed the effects of dietary capsaicin on BP in 2-kidney, 1-clip renovascular hypertension (2K1C) rats, and investigated the participation of NO in the mechanism.Methods: Rats with 2K1C or sham-operated rats (SHAM) were treated with 0.006% capsaicin diet (CAP) or control diet (CTL) for 6 weeks. Systolic BP (SBP) was measured by tail-cuff method once a week. In the end, mean arterial BP (MAP) was measured in the rats under anesthesia. These observations were performed also in the rats taking a NO synthase (NOS) inhibitor (LN). After rats were euthanized, thoracic aortas were collected and used for western blot analyses to evaluate the phosphorylated ratio of endothelial NOS (eNOS), protein kinase A (PKA) and B (Akt), in order to explore a mechanism of the effects on BP by dietary capsaicin.Results: SBP and MAP in 2K1C rats were significantly higher than in SHAM rats when fed CTL, but not when fed CAP. Those in 2K1C-CAP rats were significantly lower than in 2K1C-CTL rats. LN suppressed the effect of dietary capsaicin. The ratios of phosphorylated (p-) eNOS/eNOS and p-Akt/Akt, but not p-PKA/PKA, were significantly increased in rats fed CAP compared with rats fed CTL.Conclusion: Dietary capsaicin may alleviate 2K1C renovascular hypertension, probably via enhancing phosphorylation of Akt and eNOS.Abbreviations: 2K1C: 2-kidney, 1-clip hypertension model; Akt: protein kinase B; Ang II: angiotensin II; ANOVA: measures analysis of variance; BP: blood pressure; EC: endothelial cell; eNOS: endothelial nitric oxide synthase; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; L-NAME, LN: Nω-Nitro-L-arginine methyl ester hydrochloride; MA: mesenteric arteries; MAP: mean arterial blood pressure; NO: nitric oxide; PKA: protein kinase A; PVDF: polyvinylidene difluoride; SBP: Systolic blood pressure; SHR: spontaneously hypertensive rats; SN: sympathetic nervous; TRPV1: transient receptor potential vanilloid type 1; WKY: Wistar Kyoto rats.

Sensory effects of transient receptor potential channel agonists on whole mouth saliva extensional rheology.

The extensional rheology (ER) of saliva is a property associated with its ability to coat surfaces and is important for the maintenance of a normal mouth feeling. Transient receptor potential (TRP) channels are expressed in the oral cavity and this study investigated how the sensory effects of TRP channel agonists modify the ER of saliva. Healthy volunteers rinsed with solutions containing a TRP agonist. Unstimulated whole mouth saliva (WMS) was collected prior to rinsing and WMS was collected during the first and second minutes after the mouth rinse. The Spinnbarkeit of the collected saliva was measured using a Neva Meter. The nonivamide (TRPV1) mouth rinse increased WMS ER from 37.0 (± 6.3) mm to 49.3 (± 5.1) mm when compared with the vehicle control, which itself had no effect on WMS ER. However, this effect was short-lived and ER of WMS was not increased in the second minute after the nonivamide mouth rinse. The menthol (TRPM8) mouth rinse resulted in an increase up to 57.8 (± 7.8) mm in WMS ER from the vehicle control and returned to control levels in the second minute. The cinnamaldehyde (TRPA1) mouth rinse resulted in no change in WMS ER. It can be concluded that nonivamide and menthol mouth rinsing has a short-term effect of increasing WMS ER, an effect not observed after cinnamaldehyde rinsing. We hypothesize that the activation of some TRP channels in the oral cavity results in changes in the salivary protein composition that in turn alters WMS ER. PRACTICAL APPLICATIONS: Identifying compounds that modify the physical properties of saliva in a desirable way is important in developing treatments for conditions associated with changes in the physical properties of saliva such as xerostomia (also known as dry mouth). Furthermore, understanding the rheology of saliva contributes to the elucidation of food oral processing which is of importance to food manufacturers.

Gaining Insights into Specific Drug Formulation Additives for Solubilizing a Potential Anti-Alzheimer Disease Drug B4A1.

The pharmacological profiles of small molecule drugs are often challenged by their poor water solubility. Sequence-defined peptides attached to poly(ethylene glycol) (PEG) offer opportunities to overcome these difficulties by acting as drug-specific formulation additives. The peptide-PEG conjugates enable specific, noncovalent drug binding via tailored peptide/drug interactions as well as provide water solubility and drug shielding by well-solvated PEG-blocks. A systematic set of specific solubilizers for B4A1 as a potential anti-Alzheimer disease drug is synthesized and variations involve the length of the PEG-blocks as well as the sequences of the peptidic drug-binding domain. The solubilizer/B4A1 complexes are studied in order to understand contributions of both PEG and peptide segments on drug payload capacities, drug/carrier aggregate sizes, and influences on inhibition of the Tau-protein aggregation in an in vitro assay.

Comparison of in vitro metabolism and cytotoxicity of capsaicin and dihydrocapsaicin.

Capsaicin and dihydrocapsaicin are the major active components in pepper spray products, which are widely used for law enforcement and self-protection. The use of pepper sprays, due to their irreversible and other health effects has been under a strong debate. In this study, we compared metabolism and cytotoxicity of capsaicin and dihydrocapsaicin using human and pig liver cell fractions and human lung carcinoma cell line (A549) in vitro. Metabolites were screened and identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Using liver cell fractions, a novel aliphatic hydroxylated metabolite (m/z 322) was detected to dihydrocapsaicin but no structure was found corresponding to capsaicin. Instead, a novel phase I metabolite of capsaicin, corresponding to the structure of aliphatic demethylation and dehydrogenation (m/z 294) was identified. In addition, two novel conjugates, glycine conjugates (m/z 363 and m/z 365) and bi-glutathione (GSH) conjugates (m/z 902 and m/z 904), were identified for both capsaicin and dihydrocapsaicin. The medium of the exposed A549 cells contained ω-hydroxylated (m/z 322) and alkyl dehydrogenated (m/z 304) forms, as well as a glycine conjugate of capsaicin. As to dihydrocapsaicin, an alkyl dehydrogenated (m/z 306) form, a novel alkyl hydroxylated form, and a novel glycine conjugate were found. In A549 cells, dihydrocapsaicin evoked vacuolization and decreased cell viability more efficiently than capsaicin. Furthermore, both compounds induced p53 protein and G1 phase cell cycle arrest. Usefulness of the found metabolites as biomarkers for capsaicinoid exposures will need further investigations with additional toxicity endpoints.

Capsaicin interaction with TRPV1 channels in a lipid bilayer: molecular dynamics simulation.

Transient receptor potential vanilloid subtype 1 (TRPV1) is a heat-sensitive ion channel also involved in pain sensation, and is the receptor for capsaicin, the active ingredient of hot chili peppers. The recent structures of TRPV1 revealed putative ligand density within the S1 to S4 voltage-sensor-like domain of the protein. However, questions remain regarding the dynamic role of the lipid bilayer in ligand binding to TRPV1. Molecular dynamics simulations were used to explore behavior of capsaicin in a 1-palmitoyl-2-oleoyl phosphatidylcholine bilayer and with the target S1-S4 transmembrane helices of TRPV1. Equilibrium simulations reveal a preferred interfacial localization for capsaicin. We also observed a capsaicin molecule flipping from the extracellular to the intracellular leaflet, and subsequently able to access the intracellular TRPV1 binding site. Calculation of the potential of mean force (i.e., free energy profile) of capsaicin along the bilayer normal confirms that it prefers an interfacial localization. The free energy profile indicates that there is a nontrivial but surmountable barrier to the flipping of capsaicin between opposing leaflets of the bilayer. Molecular dynamics of the S1-S4 transmembrane helices of the TRPV1 in a lipid bilayer confirm that Y511, known to be crucial to capsaicin binding, has a distribution along the bilayer normal similar to that of the aromatic group of capsaicin. Simulations were conducted of the TRPV1 S1-S4 transmembrane helices in the presence of capsaicin placed in the aqueous phase, in the lipid, or docked to the protein. No stable interaction between ligand and protein was seen for simulations initiated with capsaicin in the bilayer. However, interactions were seen between TRPV1 and capsaicin starting from the cytosolic aqueous phase, and capsaicin remained stable in the majority of simulations from the docked pose. We discuss the significance of capsaicin flipping from the extracellular to the intracellular leaflet and mechanisms of binding site access by capsaicin.

Physiological and behavioral evidence of a capsaicin-sensitive TRPV-like channel in the medicinal leech.

Transient receptor potential vanilloid (TRPV) channels are found throughout the animal kingdom, where they play an important role in sensory transduction. In this study, we combined physiological studies with in vivo behavioral experiments to examine the presence of a putative TRPV-like receptor in the medicinal leech, building upon earlier studies in this lophotrochozoan invertebrate. The leech polymodal nociceptive neuron was activated by both peripheral and central application of the TRPV1-activator capsaicin in a concentration-dependent manner, with 100 µmol l(-1) being the lowest effective concentration. Responses to capsaicin were inhibited by the selective TRPV1 antagonist SB366791. The polymodal nociceptive neuron also responded to noxious thermal stimuli (>40°C), and this response was also blocked by SB366791. Capsaicin sensitivity was selective to the polymodal nociceptor with no direct response being elicited in the mechanical nociceptive neuron or in the non-nociceptive touch- or pressure-sensitive neurons. Capsaicin also elicited nocifensive behavioral responses (withdrawals and locomotion) in a concentration-dependent manner, and these behavioral responses were significantly attenuated with SB366791. These results suggest the presence of a capsaicin-sensitive TRPV-like channel in the medicinal leech central nervous system and are relevant to the evolution of nociceptive signaling.

Environmental risk assessment on capsaicin used as active substance for antifouling system on ships.

Biodegradation experiments were carried out with capsaicin to evaluate its degradability. The results show that capsaicin was readily biodegradable under aerobic conditions. The values of Kow and the calculated bioconcentration factor indicate that capsaicin have a low potential for bioconcentration. The fish acute toxicity tests conducted with Brachydanio rerio show LC50 for capsaicin was 5.98 mg L(-1). The tests of alga growth inhibition conducted with Selenastrum capricornutum suggest EC50 for capsaicin was 114 mg L(-1). The calculated PNEC (Predicted No Effect Concentration) was 4.9×10(-4) mg L(-1). The average PEC (Predicted Environmental Concentration) for OECD-EU commercial harbor and marina were 3.99×10(-6) and 2.49×10(-5) mg L(-1), respectively. These indicate that the PEC was much less than the PNEC for capsaicin. The low Kp value of capsaicin suggests the data about the risk of capsaicin to sediment organisms can be waived. According to the results from the analysis of the degradation, bioaccumulation, toxicity and accumulation in sediment, it can be concluded that capsaicin used as active substance for antifouling system on ships poses relatively low risk to marine environment.

In vitro skin permeation and penetration of nonivamide from novel film-forming emulsions.

The purpose of this study was to develop film-forming emulsions (FFE) facilitating long-term treatment of chronic pruritus with capsaicinoids. To this end, oil-in-water emulsions, which comprise dispersions of sustained-release polymers, were examined. Such emulsions form a film when applied to the skin and encapsulate the oily drug solution in a dry polymeric matrix. Permeation of the antipruritic drug nonivamide (NVA) is controlled by the matrix. Permeation rates of NVA from FFE and its concentration in the skin are equivalent to those achieved with a conventional semisolid formulation, but can be maintained for a longer period of time. FFE may therefore improve the treatment of chronic pruritus with capsaicinoids by enhancing patient compliance by means of a sustained-release regimen.

Ion channels in analgesia research.

Several recent techniques have allowed us to pinpoint the receptors responsible for the detection of nociceptive stimuli. Among these receptors, ion channels play a fundamental role in the recognition and transduction of stimuli that can cause pain. During the last decade, compelling evidence has been gathered on the role of the TRPV1 channel in inflammatory and neuropathic states. Activation of TRPV1 in nociceptive neurons results in the release of neuropeptides and transmitters, leading to the generation of action potentials that will be sent to higher CNS areas, where they will often be perceived as pain. Its activation will also evoke the peripheral release of pro-inflammatory compounds that may sensitize other neurons to physical, thermal, or chemical stimuli. For these reasons, and because its continuous activation causes analgesia, TRPV1 is now considered a viable drug target for clinical use in the management of pain. Using the TRPV1 channel as an example, here we describe some basic biophysical approaches used to study the properties of ion channels involved in pain and in analgesia.

Molecular assays for characterization of alternatively spliced isoforms of the u opioid receptor (MOR).

Mu-opioid receptor (MOR) belongs to a family of heptahelical G-protein-coupled receptors (GPCRs). Studies in humans and rodents demonstrated that the OPRM1 gene coding for MOR undergoes extensive alternative splicing afforded by the genetic complexity of OPRM1. Evidence from rodent studies also demonstrates an important role of these alternatively spliced forms in mediating opiate analgesia via their differential signaling properties. MOR signaling is predominantly G(ia) coupled. Release of the alpha subunit from G-protein complex results in the inhibition of adenylyl cyclase/cAMP pathway, whereas release of the betagamma subunits activates G-protein-activated inwardly rectifying potassium channels and inhibits voltage-dependent calcium channels. These molecular events result in the suppression of cellular activities that diminish pain sensations. Recently, a new isoform of OPRM1, MOR3, has been identified that shows an increase in the production of nitric oxide (NO) upon stimulation with morphine. Hence, there is a need to describe molecular techniques that enable the functional characterization of MOR isoforms. In this review, we describe the methodologies used to assay key mediators of MOR activation including cellular assays for cAMP, free Ca(2+), and NO, all of which have been implicated in the pharmacological effects of MOR agonists.

Cannabinoid CB1 receptor facilitation of substance P release in the rat spinal cord, measured as neurokinin 1 receptor internalization.

The contribution of CB1 receptors in the spinal cord to cannabinoid analgesia is still unclear. The objective of this study was to investigate the effect of CB1 receptors on substance P release from primary afferent terminals in the spinal cord. Substance P release was measured as neurokinin 1 (NK1) receptor internalization in lamina I neurons. It was induced in spinal cord slices by dorsal root stimulation and in live rats by a noxious stimulus. In spinal cord slices, the CB1 receptor antagonists AM251, AM281 and rimonabant partially but potently inhibited NK1 receptor internalization induced by electrical stimulation of the dorsal root. This was due to an inhibition of substance P release and not of NK1 receptor internalization itself, because AM251 and AM281 did not inhibit NK1 receptor internalization induced by exogenous substance P. The CB1 receptor agonist ACEA increased NK1 receptor internalization evoked by dorsal root stimulation. The effects of AM251 and ACEA cancelled each other. In vivo, AM251 injected intrathecally decreased NK1 receptor internalization in spinal segments L5 and L6 induced by noxious hind paw clamp. Intrathecal AM251 also produced analgesia to radiant heat stimulation of the paw. The inhibition by AM251 of NK1 receptor internalization was reversed by antagonists of mu-opioid and GABA(B) receptors. This indicates that CB1 receptors facilitate substance P release by inhibiting the release of GABA and opioids next to primary afferent terminals, producing disinhibition. This results in a pronociceptive effect of CB1 receptors in the spinal cord.

Structural determinants of gating in the TRPV1 channel.

Transient receptor potential vanilloid 1 (TRPV1) channels mediate several types of physiological responses. Despite the importance of these channels in pain detection and inflammation, little is known about how their structural components convert different types of stimuli into channel activity. To localize the activation gate of these channels, we inserted cysteines along the S6 segment of mutant TRPV1 channels and assessed their accessibility to thiol-modifying agents. We show that access to the pore of TRPV1 is gated by S6 in response to both capsaicin binding and increases in temperature, that the pore-forming S6 segments are helical structures and that two constrictions are present in the pore: one that impedes the access of large molecules and the other that hampers the access of smaller ions and constitutes an activation gate of these channels.

Differential effects of TRPV channel block on polymodal activation of rat cutaneous nociceptors in vitro.

The capsaicin receptor TRPV1 is a polymodal sensory transducer molecule in the pain pathway. TRPV1 integrates noxious heat, tissue acidosis and chemical stimuli which are all known to cause pain. Studies on TRPV1-deficient mice suggest that TRPV1 is essential for acid sensing by nociceptors and for thermal hyperalgesia in inflammation of the skin, but not for transducing noxious heat. After TRPV1, other TRPV channels were cloned with polymodal properties and sensitivity to noxious heat, named TRPV2, TRPV3 and TRPV4. While TRPV3 and TRPV4 are predominantly warm sensors, TRPV2's threshold is in the noxious range (>52 degrees C). However, mice deficient of TRPV2 and TRPV1 or TRPV3 or TRPV4 show no major impairment of noxious heat sensing. Ruthenium red, a water soluble polycationic dye, was found to block the pore of the capsaicin-operated cation channel TRPV1 thus interfering with all polymodal ways of TRPV1 activation. Antagonistic effects of the dye were subsequently described on many other TRP-channels, especially on the heat-sensitive ones of the vanilloid family, TRPV2, TRPV3 and TRPV4. In this study, we used the rat skin-nerve preparation to define the possible actions of ruthenium red on the proton, capsaicin and noxious heat activation of native polymodal nociceptors. Ruthenium red was found to suppress only the capsaicin-induced excitation and desensitization of these nerve endings. On the contrary, the proton and heat-induced discharge responses of the single fibres were not influenced. Additionally, we found that the dye concentration dependently increases the excitability of the neurons resulting in ongoing activity and burstlike discharge. These differential results are discussed in the light of recent findings from transgenic mouse models, and they point once more to major (pharmacological) differences between cellular models of nociception, including spinal ganglion neuron and transfected cell lines, and the real native nerve endings.

[The TRPV1 channel as a target for the treatment of pain]. / El canal TRPV1 como diana para tratar el dolor.

INTRODUCTION: Pain results from the processing of a large number of signals produced at different levels of the central and peripheral nervous system, which are generated in response to stimuli from the environment or from the organism itself. One of the strategies for generating new analgesics consists in studying the molecular bases that underlie the detection of painful stimuli, that is to say, the receptors. One receptor that plays a very important role in sensory and pain physiology is TRPV1, which is responsible for detecting mechanical, chemical and thermal stimuli. AIMS. The aim of this study is to discuss the structural and functional aspects of the TRPV1 channel, as well as its participation in certain pathological processes and the possible perspectives for clinical research. DEVELOPMENT: TRPV1 activation in sensory neurons generates signals that reach the central nervous system, where they are interpreted as pain, as well as triggering the peripheral release of pro-inflammatory substances that make other neurons sensitive to subsequent stimuli. TRPV1 is a receptor that is structurally similar to other voltage-dependent ion channels, with the capacity to detect and integrate several different stimuli from the environment, such as dangerously high temperatures or irritants. Furthermore, the activity of this channel is linked to several signalling chains related with inflammatory processes. CONCLUSIONS: The central role of TRPV1 in the physiology of pain will surely encourage the development of drugs aimed at this receptor which can be used in the treatment of several types of pain.

Release of calcitonin gene-related peptide from the jugular-nodose ganglion complex in rats--a new model to examine the role of cardiac peptidergic and nitrergic innervation.

OBJECTIVE: Afferent information from the heart and the lung is conveyed to the brainstem by primary afferent fibers originating from vagal sensory neurons (jugular-nodose ganglion complex, JNC). The present study was made to evaluate if release of the sensory neuropeptide calcitonin gene-related peptide (CGRP) from the JNC can be used as a model for future studies on changes in neuropeptide release under pathological conditions of the heart. METHODS: Freshly isolated rat JNC's were passed through a series of solutions based on oxygenated synthetic interstitial fluid (SIF). Substances such as the TRPV1 receptor agonist capsaicin and the nitric oxide (NO) donor sodium nitroprusside (SNP) were added as excitatory test stimuli. The eluates were processed using an enzyme immuno-assay (EIA) for measurement of CGRP concentrations. Immunohistochemistry was used to visualize CGRP containing and NO producing neurons in the JNC. RESULTS: Both SNP and capsaicin caused significant increases in CGRP release. CGRP-immunoreactive neurons (somata) were preferentially found in the jugular ganglion, whereas neurons immunoreactive for neuronal NO synthase were mostly localized in the nodose ganglion. CONCLUSION: The present study demonstrates an easily reproducible model for measuring stimulated CGRP release from vagal afferents arising from the JNC. Nitric oxide produced by vagal afferents may stimulate CGRP release upon afferent activation.

Capsaicin inhibits the in vitro binding of peptides selective for mu- and kappa-opioid, and nociceptin-receptors.

Capsaicin inhibited the equilibrium specific binding of endogenous opioid-like peptide ligands such as endomorphin-1, nociceptin, and dynorphin((1-17)) in rat brain membrane preparations. We studied the in vitro effect of capsaicin (1-10 microM) on homologous and heterologous competitive binding of opioid ligands, using unlabeled synthetic peptides and the following tritiated compounds: [(3)H]endomorphin-1, [(3)H]endomorphin-2, [(3)H]nociceptin((1-17)) and [(3)H]dynorphin((1-17)). Capsaicin-dependent inhibition was also observed in [(35)S]GTPgammaS stimulation assays in the presence of certain opioid peptides. The inhibition of opioid binding was further investigated using other synthetic and natural mu-opioid ligands such as [D-Ala(2),(NMe)Phe(4),Gly(5)-ol]enkephalin (DAMGO), morphine and naloxone. The decrease in opioid ligand affinity upon capsaicin treatments was most apparent with endomorphin-1, followed by nociceptin and dynorphin. The binding of other investigated opioids were not affected in the presence of capsaicin. In [(3)H]endomorphin-1 binding assays, capsazepine antagonized the inhibitory effect of capsaicin in rat brain membranes suggesting the involvement of TRPV1 receptors. In Chinese hamster ovary (CHO) cells stably expressing mu-opioid receptors, but lacking vanilloid receptors, the inhibition by capsaicin on the binding of [(3)H]endomorphin-1 was not present. It is concluded that the inhibitory effect of capsaicin on the receptor binding affinity of endogenous opioid peptides in brain membrane preparations seems not to be a direct effect, it is rather a negative feedback interaction with opioid receptors.

Phospholipase C mediated modulation of TRPV1 channels.

The transient receptor potential vanilloid type 1 (TRPV1) channels are involved in both thermosensation and nociception. They are activated by heat, protons, and capsaicin and modulated by a plethora of other agents. This review will focus on the consequences of phospholipase C (PLC) activation, with special emphasis on the effects of phosphatidylinositol 4,5-bisphosphate (PIP2) on these channels. Two opposing effects of PIP2 have been reported on TRPV1. PIP2 has been proposed to inhibit TRPV1, and relief from this inhibition was suggested to be involved in sensitization of these channels by pro-inflammatory agents. In excised patches, however, PIP2 was shown to activate TRPV1. Calcium flowing through TRPV1 activates PLC and the resulting depletion of PIP2 was proposed to play a role in capsaicin-induced desensitization of these channels. We will describe the data indicating involvement of PLC and PIP2 in sensitization and desensitization of TRPV1 and will also discuss other pathways potentially contributing to these two phenomena. We attempt to resolve the seemingly contradictory data by proposing that PIP2 can both activate and inhibit TRPV1 depending on the experimental conditions, more specifically on the level of stimulation of these channels. Finally, we also discuss data in the literature indicating that other TRP channels, TRPA1 and some members of the TRPC subfamily, may also be under a similar dual control by PIP2.

5-Hydroxytryptamine selectively activates the vagal nodose C-fibre subtype in the guinea-pig oesophagus.

The afferent neurons innervating the oesophagus originate from two embryonic sources: neurons located in vagal nodose ganglia originate from embryonic placodes and neurons located in vagal jugular and spinal dorsal root ganglia (DRG) originate from the neural crest. Here, we address the hypothesis that 5-hydroxytryptamine (5-HT) differentially stimulates afferent nerve subtypes in the oesophagus. Extracellular recordings of single unit activity originating from nerve terminals were made in the isolated innervated guinea-pig oesophagus. Whole cell patch clamp recordings (35 degrees C) were made from the primary afferent neurons retrogradely labelled from the oesophagus. 5-Hydroxytryptamine (10 micromol L(-1)) activated vagal nodose C-fibres (70%) in the oesophagus but failed to activate overtly vagal jugular nerve fibres and oesophagus-specific spinal DRG neurons. The response to 5-HT in nodose C-fibre nerve terminals was mimicked by the selective 5-HT(3) receptor agonist 2-methyl-5-HT (10 micromol L(-1)) and nearly abolished by the 5-HT(3) receptor antagonists ondansetron (10 micromol L(-1)) and Y-25130 (10 micromol L(-1)). In patch clamp studies, 2-methyl-5-HT (10 micromol L(-1)) activated a proportion of isolated oesophagus-specific nodose capsaicin-sensitive neurons (putative cell bodies of nodose C-fibres). We conclude that the responsiveness to 5-HT discriminates placode-derived (vagal nodose) C-fibres from the neural crest-derived (vagal jugular and spinal DRG) afferent nerves in the oesophagus. The response to 5-HT in nodose C-fibres is mediated by the 5-HT(3) receptor in their neuronal membrane.

Effect of cannabidiol on sepsis-induced motility disturbances in mice: involvement of CB receptors and fatty acid amide hydrolase.

Sepsis is an inflammatory condition that is associated with reduced propulsive gastrointestinal motility (ileus). A therapeutic option to treat sepsis is to promote intestinal propulsion preventing bacterial stasis, overgrowth and translocation. Recent evidence suggests that anti-oxidants improve sepsis-induced ileus. Cannabidiol, a non-psychotropic component of Cannabis sativa, exerts strong anti-oxidant and anti-inflammatory effects without binding to cannabinoid CB(1) or CB(2) receptors. Cannabidiol also regulates the activity of fatty acid amide hydrolase (FAAH) which is the main enzyme involved in endocannabinoid breakdown and which modulates gastrointestinal motility. Because of the therapeutic potential of cannabidiol in several pathologies, we investigated its effect on sepsis-induced ileus and on cannabinoid receptor and FAAH expression in the mouse intestine. Sepsis was induced by treating mice with lipopolysaccharides for 18 h. Sepsis led to a decrease in gastric emptying and intestinal transit. Cannabidiol further reduced gastrointestinal motility in septic mice but did not affect gastrointestinal motility in control mice. A low concentration of the CB(1) antagonist AM251 did not affect gastrointestinal motility in control mice but reversed the effect of cannabidiol in septic mice. Sepsis was associated with a selective upregulation of intestinal CB(1) receptors without affecting CB(2) receptor expression and with increased FAAH expression. The increase in FAAH expression was completely reversed by cannabidiol but not affected by AM251. Our results show that sepsis leads to an imbalance of the endocannabinoid system in the mouse intestine. Despite its proven anti-oxidant and anti-inflammatory properties, cannabidiol may be of limited use for the treatment of sepsis-induced ileus.

Counteracting effect of papaverine on morphine inhibition of gastrointestinal transit in mice.

Oral papaverine has been shown to be capable of antagonizing the constipation induced by a single dose of oral morphine. The primary aim of the present study was to ascertain whether papaverine is also capable of counteracting morphine-induced decrease of upper gastrointestinal transit (UGT) after repeated parenteral administration of the opioid. We next investigated the mechanisms(s) responsible for the counteracting effect of papaverine, by analysing whether this effect was changed by pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME), dexamethasone, indomethacin or capsaicin. Papaverine, co-administered with morphine, counteracted the morphine-induced decrease in UGT in mice pretreated with morphine for 3 days but did not do so in naive animals. The counteracting effect of papaverine was antagonized by L-NAME, but not by indomethacin. In mice pretreated with both morphine and dexamethasone, papaverine failed to antagonize the effect of morphine. Capsaicin pretreatment completely abolished the effect of a single dose of morphine, the effect being partially restored by the 3 days pretreatment with morphine. In mice pretreated with both capsaicin and morphine, the UGT decrease elicited by morphine was lower than in the other experimental groups and was not modified by papaverine. Our results show that papaverine can counteract the morphine inhibition of UGT in mice repeatedly exposed to the opioid. Papaverine exerts its action through a nitric oxide synthase-mediated mechanism; this mechanism is only effective after repeated morphine administration and does not operate when capsaicin-sensitive afferent neurones are ablated.