Pharmacology and Therapeutics of Bronchodilators Revisited.

Bronchodilators remain the cornerstone of the treatment of airway disorders such as asthma and chronic obstructive pulmonary disease (COPD). There is therefore considerable interest in understanding how to optimize the use of our existing classes of bronchodilator and in identifying novel classes of bronchodilator drugs. However, new classes of bronchodilator have proved challenging to develop because many of these have no better efficacy than existing classes of bronchodilator and often have unacceptable safety profiles. Recent research has shown that optimization of bronchodilation occurs when both arms of the autonomic nervous system are affected through antagonism of muscarinic receptors to reduce the influence of parasympathetic innervation of the lung and through stimulation of ß 2-adrenoceptors (ß 2-ARs) on airway smooth muscle with ß 2-AR-selective agonists to mimic the sympathetic influence on the lung. This is currently achieved by use of fixed-dose combinations of inhaled long-acting ß 2-adrenoceptor agonists (LABAs) and long-acting muscarinic acetylcholine receptor antagonists (LAMAs). Due to the distinct mechanisms of action of LAMAs and LABAs, the additive/synergistic effects of using these drug classes together has been extensively investigated. More recently, so-called "triple inhalers" containing fixed-dose combinations of both classes of bronchodilator (dual bronchodilation) and an inhaled corticosteroid in the same inhaler have been developed. Furthermore, a number of so-called "bifunctional drugs" having two different primary pharmacological actions in the same molecule are under development. This review discusses recent advancements in knowledge on bronchodilators and bifunctional drugs for the treatment of asthma and COPD. SIGNIFICANCE STATEMENT: Since our last review in 2012, there has been considerable research to identify novel classes of bronchodilator drugs, to further understand how to optimize the use of the existing classes of bronchodilator, and to better understand the role of bifunctional drugs in the treatment of asthma and chronic obstructive pulmonary disease.

The anti-proliferative effects of adiponectin on human lung adenocarcinoma A549 cells and oxidative stress involvement.

Adiponectin (Acrp30) plays an important role in energy metabolism and inflammation. Recently, in vivo serum Acrp30 levels have been reported to be correlated to risk of developing several types of cancers such as lung cancer, and in vitro studies have demonstrated a role for Acrp30 in the control of cell proliferation and survival. However, the molecular effects of Acrp30 on lung cancer have not yet been clearly defined. In the present study, we investigated the effects of different concentrations of Acrp30 on the A549 human alveolar epithelial cell line, an in vitro model of lung adenocarcinoma. A549 cells were exposed to various concentrations of Acrp30 and successively, proliferation, apoptosis and oxidative stress were evaluated by MTT test, caspase activity assay, flow-cytometry and western blotting analysis. Our results demonstrated that Acrp30 causes, in a time- and dose-dependent manner, a reduction of cell viability and duplication together with an increase in cell apoptosis rate. In addition, we found that Acrp30 induces an increase of lipid peroxidation evaluated by TBARS assay and a concomitant reduction of nitric oxide release, both markers of cellular oxidative stress. Taken together, our data on A549 cells provides new insight into potential involvement of Acrp30 on physio-pathologic mechanisms of lung diseases through interference with proliferation, apoptosis and oxidative status.

Combining long-acting bronchodilators with different mechanisms of action: A pharmacological approach to optimize bronchodilation of equine airways.

The ultra long-acting ß2 -adrenoceptor agonist olodaterol plus the ultra long-acting muscarinic antagonist tiotropium bromide are known to relax equine airways. In human bronchi combining these drugs elicits a positive interaction, thus we aimed to characterize this information further in equine isolated airways stimulated by electrical field stimulation (EFS) and using the Concentration-Reduction Index (CRI) and Combination Index (CI) equations. The drugs were administered alone and together by reproducing ex vivo the concentration-ratio delivered by the currently available fixed-dose combination (1:1). The single agents elicited a significant (p < .05) concentration-dependent reduction in the EFS-induced contractility, that was synergistically improved (CI 0.18) when administered in combination (0.9 logarithms more potent, 24% more effective than the monocomponents). The drugs mixture allowed a reduction in the concentration of olodaterol from ≃1 to ≃2.3 logarithms. A favorable CRI was detected also for tiotropium bromide, whose concentration can be reduced ≃1 logarithm at medium effect levels, remaining positive up to submaximal relaxant effect in the presence of olodaterol. The combination of tiotropium bromide/olodaterol allows the reduction in the concentration of the monocomponents to achieve airway smooth muscle relaxation, thus potentially decreases the risk of adverse events when these drugs are used to treat severe asthmatic horses.

Pharmacology and therapeutics of bronchodilators.

Bronchodilators are central in the treatment of of airways disorders. They are the mainstay of the current management of chronic obstructive pulmonary disease (COPD) and are critical in the symptomatic management of asthma, although controversies around the use of these drugs remain. Bronchodilators work through their direct relaxation effect on airway smooth muscle cells. at present, three major classes of bronchodilators, ß(2)-adrenoceptor (AR) agonists, muscarinic receptor antagonists, and xanthines are available and can be used individually or in combination. The use of the inhaled route is currently preferred to minimize systemic effects. Fast- and short-acting agents are best used for rescue of symptoms, whereas long-acting agents are best used for maintenance therapy. It has proven difficult to discover novel classes of bronchodilator drugs, although potential new targets are emerging. Consequently, the logical approach has been to improve the existing bronchodilators, although several novel broncholytic classes are under development. An important step in simplifying asthma and COPD management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence. Several once-daily ß(2)-AR agonists or ultra-long-acting ß(2)-AR-agonists (LABAs), such as indacaterol, olodaterol, and vilanterol, are already in the market or under development for the treatment of COPD and asthma, but current recommendations suggest the use of LABAs only in combination with an inhaled corticosteroid. In addition, some new potentially long-acting antimuscarinic agents, such as glycopyrronium bromide (NVA-237), aclidinium bromide, and umeclidinium bromide (GSK573719), are under development, as well as combinations of several classes of long-acting bronchodilator drugs, in an attempt to simplify treatment regimens as much as possible. This review will describe the pharmacology and therapeutics of old, new, and emerging classes of bronchodilator.

Effects of chronic administration of ß-blockers on airway responsiveness in a murine model of heart failure.

Lung function abnormalities, both at rest and during exercise, are frequently observed in patients with chronic heart failure (HF), also in absence of respiratory disease. It has been documented that, in HF, chronic adrenergic stimulation down-regulates ß-adrenoceptors (ß-ARs) and modifies airway relaxant responses. This study was designed to investigate in an animal model of HF whether a treatment with a ß-AR blocker, metoprolol, could modify the altered airway hyperresponsiveness. In rats, randomly assigned to 3 experimental groups sham-operated rats (SH), rats with HF induced by left anterior descending coronaric occlusion (HF n = 10), and rats treated with metoprolol 100 mg/kg/die (MET = 10), HF was evaluated after 10 weeks and resulted in increases in plasma norepinephrine and epinephrine and left ventricular end diastolic pressure. ß2-ARs and G-protein-ßAR2-kinase (GRK2) mRNA levels were determined by real time reverse transcriptase PCR. Carbachol-precontracted isolated tracheal rings were used to functionally assess airway smooth muscle relaxation. In pulmonary tissues, ß2-AR mRNA level was significantly decreased in HF groups (-48.73 ± 5.18%, P < 0.01); in the same groups the GRK2 mRNA-levels were significantly enhanced (+222.50 ± 6.13%, P < 0.001); in lung deriving from MET groups the levels of mRNA were significantly increased (+339.86 ± 11.26%, P < 0.001), while the GRK2 mRNA-levels unchanged (-59.02 ± 3.97%, P < 0.001), when compared to SH groups. Relaxation of tracheal strips in response to salbutamol was significantly reduced in HF groups; in tracheal rings, deriving from MET groups, the relaxant effects of salbutamol were significantly enhanced (SH, Emax: 34.87 ± 2.98%, pD2: 7.45 ± 0.27; HF, Emax: 34.87 ± 2.98%, pD2: 7.45 ± 0.27; MET, Emax: 85.43 ± 6.80%, pD2: 6.95 ± 0.59, P < 0.001). In HF, the down-regulation of pulmonary ß-ARs results in a significant attenuation of airway relaxation. These effects have been reversed by a treatment with metoprolol, suggesting a potential role of ß-AR blockers in the treatment of patients suffering from HF and chronic obstructive airway diseases.

ß2-agonist therapy in lung disease.

ß2-Agonists are effective bronchodilators due primarily to their ability to relax airway smooth muscle (ASM). They exert their effects via their binding to the active site of ß2-adrenoceptors on ASM, which triggers a signaling cascade that results in a number of events, all of which contribute to relaxation of ASM. There are some differences between ß2-agonists. Traditional inhaled short-acting ß2-agonists albuterol, fenoterol, and terbutaline provide rapid as-needed symptom relief and short-term prophylactic protection against bronchoconstriction induced by exercise or other stimuli. The twice-daily ß2-agonists formoterol and salmeterol represent important advances. Their effective bronchodilating properties and long-term improvement in lung function offer considerable clinical benefits to patients. More recently, a newer ß2-agonist (indacaterol) with a longer pharmacodynamic half-life has been discovered, with the hopes of achieving once-daily dosing. In general, ß2-agonists have an acceptable safety profile, although there is still controversy as to whether long-acting ß2-agonists may increase the risk of asthma mortality. In any case, they can induce adverse effects, such as increased heart rate, palpitations, transient decrease in PaO2, and tremor. Desensitization of ß2-adrenoceptors that occurs during the first few days of regular use of ß2-agonist treatment may account for the commonly observed resolution of the majority of these adverse events after the first few doses. Nevertheless, it can also induce tolerance to bronchoprotective effects of ß2-agonists and has the potential to reduce bronchodilator sensitivity to them. Some novel once-daily ß2-agonists (olodaterol, vilanterol, abediterol) are under development, mainly in combination with an inhaled corticosteroid or a long-acting antimuscarinic agent.

LABAs in asthmatic children: highlights and new inside.

International asthma guidelines recommend increasing the dose of ICS or adding leukotriene modifiers or the use of long-acting inhaled beta2-agonists (LABAs) in combination with inhaled corticosteroids (ICS) when uncontrolled asthma occurs in adult and children in treatment with low-dose inhaled corticosteroids. However, in children, the effects of this last treatment option are unclear because there are few studies on the efficacy and safety of these drugs in pediatric age. Furthermore, salmeterol is licensed for use in children over 4 years and formoterol in children of more than 6 years. Finally, recent data provides evidence that repeated bronchoconstriction induces epithelial cell stress that may lead to remodeling and these findings may have potential implications for asthma management, particularly for LABAs treatment in the future.

Prolonged-release pirfenidone in patients with pulmonary fibrosis as a phenotype of post-acute sequelae of COVID-19 pneumonia. Safety and efficacy.

INTRODUCTION: One of the major concerns with post-acute sequelae of COVID-19 (PASC) is the development of pulmonary fibrosis, for which no approved pharmacological treatment exists. Therefore, the primary aim of this open-label study was to evaluate the safety and the potential clinical efficacy of a prolonged-release pirfenidone formulation (PR-PFD) in patients having PASC-pulmonary fibrosis. METHODS: Patients with PASC-pulmonary fibrosis received PR-PFD 1800 mg/day (1200 mg in the morning after breakfast and 600 mg in the evening after dinner) for three months. Blood samples were taken to confirm the pharmacokinetics of PR-PFD, and adverse events (AEs) were evaluated monthly using a short questionnaire. Symptoms, dyspnea, and pulmonary function tests (spirometry, diffusing capacity for carbon monoxide, plethysmography, and 6-min walk test [6MWT]) were evaluated at baseline, and one and three months after having started the PR-PFD treatment. RESULTS: Seventy subjects with mild to moderate lung restriction were included. The most common AEs were diarrhea (23%), heartburn (23%), and headache (16%), for which no modifications in the drug study were needed. Two patients died within the first 30 days of enrolment, and three opted not to continue the study, events which were not associate with PR-PFD. Pulmonary function testing, 6MWT, dyspnea, symptoms, and CT scan significantly improved after three months of treatment with PR-PFD. CONCLUSION: In patients with PASC pulmonary fibrosis, three months' treatment with PR-PFD was safe and showed therapeutic efficacy. Still, it remains to be seen whether the pulmonary fibrotic process remains stable, becomes progressive or will improve.

Emerging anti-inflammatory strategies for COPD.

The hallmark of chronic obstructive pulmonary disease (COPD) is an enhanced or abnormal inflammatory immune response of the lungs to inhaled particles and gases, usually from cigarette smoke, characterised by increased numbers of neutrophils, activated macrophages and activated T-lymphocytes (Tc1 and Th1 cells). Therefore, suppression of the inflammatory response is a logical approach to the treatment of COPD. Despite the inflammatory nature of COPD, currently available anti-inflammatory therapies provide little or no benefit in COPD patients and may have detrimental effects. For this reason, there is an urgent need to discover effective and safe anti-inflammatory treatments that might prevent the relentless progression of the disease. In recent years, attention has largely been focused on inhibition of recruitment and activation of inflammatory cells, and on antagonism of their products. In this review, we put together a summary of the state-of-the-art development of clearly and/or potentially useful anti-inflammatory strategies in COPD.

Emerging inhaled bronchodilators: an update.

Bronchodilators remain central to the symptomatic management of chronic obstructive pulmonary disease and asthma, and, for this reason and also because the patent protection of many bronchodilators has expired, several companies have reinitiated research into the field. The only limits set for the development of a long-lasting bronchodilator with a new product profile are medical needs and marketing opportunities. The incorporation of once-daily dose administration is an important strategy for improving adherence and is a regimen preferred by most patients. A variety of beta(2)-agonists and antimuscarinic agents with longer half-lives and inhalers containing a combination of several classes of long-acting bronchodilator are currently under development. The present article reviews all of the most important compounds under development, describing what has been done and discussing their genuine advantage.

Novel long-acting bronchodilators for COPD and asthma.

An important step in simplifying asthma and chronic obstructive pulmonary disease (COPD) management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence and is a regimen preferred by most patients, which may also lead to enhancement of compliance, and may have advantages leading to improved overall clinical outcomes. Once-daily beta2-agonists or ultra long-acting beta2-agonists (LABAs) such as carmoterol, indacaterol, GSK-159797, GSK-597901, GSK-159802, GSK-642444 and GSK-678007 are under development for the treatment of asthma and COPD. Also some new long-acting antimuscarinic agents (LAMAs) such as aclidinium, LAS-35201, GSK656398, GSK233705, NVA-237 (glycopyrrolate) and OrM3 are under development. In any case, the current opinion is that it will be advantageous to develop inhalers containing combination of several classes of long-acting bronchodilator drugs in an attempt to simplify treatment regimens as much as possible. Consequently, several options for once-daily dual-action ultra LABA+LAMA combination products are currently being evaluated. A different approach is to have a dimer molecule in which both pharmacologies are present (these molecules are known as M3 antagonist-beta2 agonist (MABA) bronchodilators). The advent of a successful MABA product will revolutionize the field and open the door for a new range of combination products.

Mitochondrial dysfunction in rat brain with aging Involvement of complex I, reactive oxygen species and cardiolipin.

Reactive oxygen species (ROS) are considered a key factor in brain aging process. Mitochondrial respiration is an important site of ROS production and hence a potential contributor to brain functional changes with aging. In this study we examined the effect of aging on complex I activity, oxygen consumption, ROS production and phospholipid composition in rat brain mitochondria. The activity of complex I was reduced by 30% in brain mitochondria from 24 months aged rats relative to young animals. These changes in complex I activity were associated with parallel changes in state 3 respiration. H(2)O(2) generation was significantly increased in mitochondria isolated from aged rats. The mitochondrial content of cardiolipin, a phospholipid required for optimal activity of complex I, decreased by 31% as function of aging, while there was a significant increase in the level of peroxidized cardiolipin. The age-related decrease in complex I activity in brain mitochondria could be reversed by exogenously added cardiolipin. This effect of cardiolipin could not be replaced by other phospholipids. It is proposed that aging causes brain mitochondrial complex I dysfunction which can be attributed to ROS-induced cardiolipin oxidation. These findings may prove useful in elucidating the mechanism underlying mitochondrial dysfunction associated with brain aging.

Codon 129 polymorphism of prion protein gene in sporadic Alzheimer's disease.

Codon 129 polymorphism of the prion protein gene represents a major genetic risk factor for Creutzfeldt-Jakob disease (CJD). Both CJD and Alzheimer's disease (AD) are brain amyloidoses and it would be possible that codon 129 polymorphism plays a role in the susceptibility to AD. In order to investigate this polymorphism in AD the distribution of polymorphic codon 129 of the PRNP gene in 194 probable AD and 124 controls selected in Italy and 109 neuropathologically verified AD and 58 matched controls recruited in the USA was studied. No significant association was found for the PRNP polymorphism in AD compared to controls either in Probable or in Definite AD series even after stratification for APOE polymorphism. This study does not support a role of PRNP polymorphism as a susceptibility factor for AD.

Clinical effect of corticosteroids in asthma-affected horses: A quantitative synthesis.

BACKGROUND: There are limited findings from low-powered studies based on few number of subjects with equine asthma. Furthermore, no studies have been performed to assess a meaningful clinically detectable impact of corticosteroids in equine asthma. OBJECTIVES: To assess and compare the clinical effect of inhaled and systemic corticosteroids in equine asthma and identify a quantitative clinical score suitable to assess the Minimal Important Difference (MID), expressed as the Minimally Clinically Detectable Difference (MCDD). STUDY DESIGN: Pair-wise and network meta-analysis. METHODS: Literature searches for studies on corticosteroid therapy in equine asthma were performed. The risk of publication bias was assessed by Funnel plots and Egger's test. The effect on changes in clinical scores vs. control was analysed via random-effects models and Bayesian networks. RESULTS: Corticosteroids significantly improved the clinical condition (Standardised Mean Difference: -1.52, 95% CrI -2.07 to -0.98; P<0.001 vs. control). No difference was detected between inhaled and systemic corticosteroids with regard to the changes in clinical scores (Relative Effect: 0.08, 95% CrI -1.45 to 1.32; P = 0.8). An Improved clinically Detectable Equine Asthma Scoring System (IDEASS) indicated that corticosteroids improved the clinical condition of asthmatic horses by 30% compared with controls (IDEASS value: -2.36, 95% CI -3.39 to -1.33; P<0.001). A one-point change in IDEASS represented the MCDD in equine asthma. MAIN LIMITATIONS: Moderate quality of evidence for systemic corticosteroids. CONCLUSIONS: Inhaled corticosteroids are effective in improving the clinical condition of horses with equine asthma and prevent exacerbations. Systemic corticosteroids should be used only in selected cases with symptomatic airway hyperresponsiveness during exacerbation. IDEASS requires further validation but may represent a suitable approach to rank the level of asthma severity and assess the clinical effect of pharmacotherapy in horses with equine asthma.

Benralizumab for the treatment of asthma.

Benralizumab is a humanized monoclonal antibody directed at the a subunit of the interleukin-5 receptor (IL-5R) that is under clinical development. The binding of benralizumab with the alpha chain of IL-5R results in inhibition of hetero-oligomerization of alpha and beta subunits and thus no signal transduction occurs. Consequently, this inhibition prevents proliferation of eosinophils and basophils and the cascade of events following it. Several pivotal trials have documented that benralizumab reduces asthma exacerbation rates with a significant increase in time to the next exacerbation, statistically improves prebronchodilator forced expiratory volume in 1 second (FEV1) and disease-specific health-related quality of life, and is well tolerated in patients with severe asthma and blood eosinophil counts greater than or equal to 150 cells/mcL.

Pharmacological treatments in asthma-affected horses: A pair-wise and network meta-analysis.

BACKGROUND: Equine asthma is a disease characterised by reversible airflow obstruction, bronchial hyper-responsiveness and airway inflammation following exposure of susceptible horses to specific airborne agents. Although clinical remission can be achieved in a low-airborne dust environment, repeated exacerbations may lead to irreversible airway remodelling. The available data on the pharmacotherapy of equine asthma result from several small studies, and no head-to-head clinical trials have been conducted among the available medications. OBJECTIVES: To assess the impact of the pharmacological interventions in equine asthma and compare the effect of different classes of drugs on lung function. STUDY DESIGN: Pair-wise and network meta-analysis. METHODS: Literature searches for clinical trials on the pharmacotherapy of equine asthma were performed. The risk of publication bias was assessed by funnel plots and Egger's test. Changes in maximum transpulmonary or pleural pressure, pulmonary resistance and dynamic lung compliance vs. control were analysed via random-effects models and Bayesian networks. RESULTS: The results obtained from 319 equine asthma-affected horses were extracted from 32 studies. Bronchodilators, corticosteroids and chromones improved maximum transpulmonary or pleural pressure (range: -8.0 to -21.4 cmH2 O; P<0.001). Bronchodilators, corticosteroids and furosemide reduced pulmonary resistance (range: -1.2 to -1.9 cmH2 O/L/s; P<0.001), and weakly increased dynamic lung compliance. Inhaled ß2 -adrenoreceptor (ß2 -AR) agonists and inhaled corticosteroids had the highest probability of being the best therapies. Long-term treatments were more effective than short-term treatments. MAIN LIMITATIONS: Weak publication bias was detected. CONCLUSIONS: This study demonstrates that long-term treatments with inhaled corticosteroids and long-acting ß2 -AR agonists may represent the first choice for treating equine asthma. Further high quality clinical trials are needed to clarify whether inhaled bronchodilators should be preferred to inhaled corticosteroids or vice versa, and to investigate the potential superiority of combination therapy in equine asthma.

Effect of formoterol/budesonide combination on arterial blood gases in patients with acute exacerbation of COPD.

BACKGROUND: Patients with severe chronic airway obstruction might suffer dangerous hypoxemia after administration of a beta-agonist despite bronchodilation. METHODS: We first compared the acute effects on gas exchange of two doses of formoterol Turbuhaler (9 and 18 microg) in 10 patients with acute exacerbation of COPD. Afterwards, we compared the acute effects of formoterol Turbuhaler 9 microug with those of formoterol/budesonide combination in a single inhaler (Turbuhaler) 9/320 microg in 10 other patients with acute exacerbation of COPD. Finally, we compared the changes in PaO(2) induced by formoterol Turbuhaler 9 microg or formoterol/budesonide combination in a single inhaler (Turbuhaler) 9/320 microg with those in FEV(1) in 10 other patients with acute exacerbation of COPD. Each agent was given on separate days, and the patients' arterial blood gases were measured at baseline and at intervals of 120 min. RESULTS: Small but statistically significant declines in PaO(2) were found after administration of both formoterol 9 and 18 microg. In the second group of patients, formoterol 9 microg alone again induced a significant decrease in PaO(2). However, the simultaneous administration of budesonide 320 microg significantly reduced the acute effect of formoterol on PaO(2). In a third group of 10 patients we confirmed a small but significant decrease in PaO(2) after formoterol alone and the reduction of this effect when budesonide was administered simultaneously. Moreover, we also documented that addition of budesonide amplified the fast onset of action of formoterol. CONCLUSIONS: These results suggest that when treating patients suffering from acute exacerbation of COPD with formoterol, it is prudent to check their arterial blood gases. In any case, combined administration of formoterol and budesonide reduces the potential for acute effects of formoterol on blood-gas tensions.

Comparison of the acute effect of tiotropium versus a combination therapy with single inhaler budesonide/formoterol on the degree of resting pulmonary hyperinflation.

In 20 COPD patients (FEV(1) < or =65% predicted, IC<80% predicted), we evaluated changes in the degree of pulmonary hyperinflation after acute administration of tiotropium 18 microg or budesonide/formoterol 320/9 microg. The study consisted of a screening visit and two study days separated by at least one week. Functional parameters were measured before and 30, and 120 min after inhalation of single study drug. Both tiotropium and budesonide/formoterol induced significant changes in functional parameters after 30 and 120 min. However, the impact of tiotropium on the degree of pulmonary hyperinflation was larger than that of budesonide/formoterol, although only differences in IC and TGV between the two treatments were significant (P<0.05), at least after 120 min, whereas those in RV were not significant. The documentation that tiotropium is able to modify IC even after an acute administration indicates its capacity of influencing expiratory flow limitation in a very fast manner and this is an important finding. In fact, changes in IC after bronchodilators in patients with COPD with expiratory flow limitation at rest may represent an objective tool for prescribing these drugs to attain symptomatic improvement and better quality of life, even in the absence of a significant increase in FEV(1).

Anandamide excites central terminals of dorsal root ganglion neurons via vanilloid receptor-1 activation.

Recently, the cannabinoid (CB) receptor agonist anandamide (AEA) has been shown to excite perivascular terminals of primary sensory neurons via activation of the vanilloid receptor-1 (VR-1). To determine whether AEA stimulates central terminals of these neurons, via VR-1 activation, we studied the release of calcitonin gene-related peptide (CGRP)- and substance P (SP)-like immunoreactivities (LI) from slices of rat dorsal spinal cord. Mobilization of Ca(2+) in rat dorsal root ganglion (DRG) neurons in culture was also studied. AEA (0.1-10 micrometer) increased the outflow of CGRP-LI and SP-LI from slices of the rat dorsal spinal cord in a Ca(2+)-dependent manner and increased [Ca(2+)](i) in capsaicin-sensitive cultured DRG neurons. Both effects of AEA were abolished by capsaicin pretreatment and by the VR-1 antagonist capsazepine but not affected by the CB receptor antagonists AM281 or AM630. Both neuropeptide release and Ca(2+) mobilization induced by electrical field stimulation (EFS) were inhibited by a low concentration of AEA (10 nm). Inhibition by AEA of EFS-induced responses was reversed by AM281 and AM630, but was not affected by capsazepine. Results indicate that stimulation of VR-1 with high concentrations of AEA excites central terminals of capsaicin-sensitive DRG neurons, thus causing neuropeptide release in the dorsal spinal cord. This novel activity opposes the CB receptor-mediated inhibitory action of low concentrations AEA. However, only if large amounts of endogenous AEA could be produced at the level of the dorsal spinal cord, they may not inhibit, but rather activate, nociceptive sensory neurons.