Antitussive profile of the NOP agonist Ro-64-6198 in the guinea pig

We have previously shown that N/OFQ, the endogenous peptide ligand for the 'opioid-like' NOP receptor, inhibits cough in guinea pigs and cats. In the present study we sought to continue our characterization of the cough-suppressant effects of NOP stimulation by profiling the pulmonary and antitussive effects of a novel non-peptide NOP agonist, Ro-64-6198, in guinea pigs. In receptor-binding assays, we confirmed that Ro-64-6198 selectively binds to NOP receptors over other opioid receptors. The Ki values for Ro-64-6198 at NOP, MOP, KOP and DOP receptors was 0.3, 36, 214 and 3,787 nmol/l, respectively. In GTPgammaS-binding assays, Ro-64-6198 displayed >900-fold functional selectivity at NOP relative to MOP receptors. We evaluated the effects of Ro-64-6198 (3 and 10 micromol/l) in isolated guinea pig nodose ganglia cells on the increases in intracellular Ca2+ concentration evoked by capsaicin stimulation (1 x 10(-8)-1 x 10(-6) mol/l). Similar to previously reported data with N/OFQ, Ro-64-6198 (3 and 10 micromol/l) significantly attenuated Ca2+ responses in nodose ganglia cells produced by exposure to capsaicin. The effect of Ro-64-6198 (3 micromol/l) on capsaicin-induced intracellular Ca2+ responses was blocked by the NOP antagonist, J113397 (3 micromol/l). In guinea pig in vivo studies, aerosolized capsaicin (10-300 micromol/l) produced a dose-dependent increase in cough number. Ro-64-6198 given i.p. significantly inhibited cough due to capsaicin (300 micromol/l) exposure. In a duration study we found that the maximum antitussive effect (42 +/- 8% inhibition) of Ro-64-6198 (3 mg/kg) was observed at 1 h after i.p. administration. Also at 1 h after administration, Ro-64-6198 (0.003-3.0 mg/kg, i.p.) produced a dose-dependent inhibition of cough. The antitussive effect of Ro-64-6198 (3 mg/kg, i.p.) was blocked by J113397 (12 mg/kg, i.p.) but not by the classical opioid antagonist naltrexone (10 mg/kg, i.p.). Although the antitussive action of Ro-64-6198 may be mediated by a central and/or a peripheral site of action, we hypothesize that selective oral NOP agonists that do not penetrate the blood-brain barrier may provide a novel approach for the treatment of cough. Moreover, because these drugs do not interact at MOP receptors, they may be devoid of codeine-like side effects such as respiratory depression, sedation, constipation or proclivities for addictive liabilities.     

Comparison of TRPA1-versus TRPV1-mediated cough in guinea pigs

TRPA1 receptor is activated by endogenous inflammatory mediators and exogenous pollutant molecules relevant to respiratory diseases. Previous studies have implicated TRPA1 as a drug target for antitussive therapy. Here we evaluated the relative efficacy of TRPA1 activation to evoke cough. In conscious guinea pigs the TRPA1 agonist allyl-isothiocyanate (AITC) evoked cough with a maximally effective concentration of 10mM that was abolished by the selective TRPA1 antagonist AP-18. AITC (10mM) was approximately 3-times less effective in inducing cough than capsaicin (50 μM). Ex vivo single fiber extracellular recordings revealed that, similarly to capsaicin, AITC evoked activation in airway jugular C-fibers, but not in airway nodose Aδ-fibers. Consistent with the cough studies, AITC was approximately 3-times less effective than capsaicin in evoking sustained activation of the jugular C-fibers. Another TRPA1 agonist, cinnamaldehyde, was approximately twofold more effective than AITC in inducing cough. However, the cinnamaldehyde (10mM)-induced cough was only partially inhibited by the TRPA1 antagonist AP-18, and was abolished by combination of AP-18 and the TRPV1 antagonist I-RTX. We conclude that in na?ve guinea pigs, TRPA1 activation initiates cough that is relatively modest compared to the cough initiated by TRPV1, likely due to lower efficacy of TRPA1 stimulation to induce sustained activation of airway C-fibers.     

治咳川贝枇杷滴丸镇咳平喘作用研究

目的：研究治咳川贝枇杷滴丸对豚鼠的镇咳、平喘作用。方法：采用豚鼠离体气管平滑肌收缩实验和组胺引喘的活体动物实验对治咳川贝枇杷滴丸的平喘作用进行评价。在离体实验中测定药物对乙酰胆碱引起的气管平滑肌收缩的收缩曲线,计算收缩百分率;在整体动物实验中测定给药后豚鼠的延喘时间用来表征药物平喘作用的强弱。同时采用枸橼酸诱发豚鼠咳嗽模型,通过记录引咳后5min内的咳嗽次数,观察治咳川贝枇杷滴丸的镇咳作用。结果：治咳川贝枇杷滴丸能有效减少豚鼠的咳嗽次数,显著延长咳嗽潜伏期;对豚鼠离体气管收缩的抑制效果较好;对组胺致喘豚鼠的哮喘潜伏期有明显的延长作用。结论：治咳川贝枇杷滴丸具有良好的镇咳、平喘药理活性,为药物的临床应用和进一步开发提供了依据。     

Inhibition of guinea-pig and human sensory nerve activity and the cough reflex in guinea-pigs by cannabinoid (CB2) receptor activation

1. There is considerable interest in novel therapies for cough, since currently used agents such as codeine have limited beneficial value due to the associated side effects. Sensory nerves in the airways mediate the cough reflex via activation of C-fibres and RARs. Evidence suggests that cannabinoids may inhibit sensory nerve-mediated responses. 2. We have investigated the inhibitory actions of cannabinoids on sensory nerve depolarisation mediated by capsaicin, hypertonic saline and PGE2 on isolated guinea-pig and human vagus nerve preparations, and the cough reflex in conscious guinea-pigs. 3. The non-selective cannabinoid (CB) receptor agonist, CP 55940, and the selective CB2 agonist, JWH 133 inhibited sensory nerve depolarisations of the guinea-pig vagus nerve induced by hypertonic saline, capsaicin and PGE2. These responses were abolished by the CB2 receptor antagonist SR144528, and unaffected by the CB1 antagonist SR141716A. Similarly, JWH 133 inhibited capsaicin-evoked nerve depolarisations in the human vagus nerve, and was prevented by SR144528. 4. Using a guinea-pig in vivo model of cough, JWH 133 (10 mg kg-1, i.p., 20 min) significantly reduced citric acid-induced cough in conscious guinea pigs compared to those treated with the vehicle control. 5. These data show that activation of the CB2 receptor subtype inhibits sensory nerve activation of guinea-pig and human vagus nerve, and the cough reflex in guinea-pigs, suggesting that the development of CB2 agonists, devoid of CB1-mediated central effects, will provide a new and safe antitussive treatment for chronic cough.     

清肺消炎丸对豚鼠的镇咳平喘作用研究

目的：研究清肺消炎丸对豚鼠的镇咳平喘作用。方法：采用枸橼酸诱发豚鼠咳嗽模型,记录引咳后3min内的咳嗽次数,观察清肺消炎丸的镇咳作用。采用豚鼠离体气管平滑肌收缩实验和组胺引喘的活体动物实验对清肺消炎丸的平喘作用进行评价。离体实验中测定药物对乙酰胆碱引起的气管平滑肌收缩的收缩曲线,计算收缩百分率;整体动物实验中测定给药后豚鼠的延喘时间用来表征药物平喘作用的强弱。结果：清肺消炎丸能有效减少豚鼠的咳嗽次数,显著延长咳嗽潜伏期;对豚鼠离体气管收缩的抑制效果较好：对组胺致喘豚鼠的哮喘潜伏期有明显的延长作用。结论：清肺消炎丸具有良好的镇咳、平喘药理活性,为药物的临床应用和进一步开发提供了依据。     

Peripheral and central sites of action of GABA-B agonists to inhibit the cough reflex in the cat and guinea pig.

1. The GABA-B receptor agonists baclofen and 3-aminopropylphosphinic acid (3-APPi) have antitussive activity in the cat and guinea pig. The purpose of this study was to investigate the sites of action of these GABA-B receptor agonists to inhibit the cough reflex. 2. Single intracerebroventricular (i.c.v.) cannulas were placed in the lateral ventricles of anaesthetized guinea pigs. Approximately 1 week later, the animals were exposed to aerosols of capsaicin (0.3 mM) to elicit coughing. Coughs were detected with a microphone and counted. 3. Cough was produced in anaesthetized cats by mechanical stimulation of the intrathoracic trachea and was recorded from electromyograms of respiratory muscle activity. Cannulas were placed for intravenous (i.v.) or, in separate groups of animals, intravertebral arterial (i.a.) administration of baclofen, 3-APPi, the centrally active antitussive drug codeine or the peripherally active antitussive drug BW443c. Dose-response relationships for i.v. and i.a. administration of each drug were generated to determine a ratio of i.v. ED50 to i.a. ED50, known as the effective dose ratio (EDR). The EDR will be 20 or greater for a centrally acting drug. 4. In the guinea pig, baclofen (3 mg kg-1, s.c.) and 3-APPi (10 mg kg-1, s.c.) inhibited capsaicin-induced cough by 50% and 35% respectively. The antitussive activity of baclofen was completely blocked by i.c.v. administration of the GABA-B receptor antagonist CGP 35348 (10 micrograms). Conversely, the antitussive effect of 3-APPi was unaffected by i.c.v. CGP 35348. However, systemic administration of CGP 35348 (30 mg kg-1, s.c.) completely blocked the antitussive activity of 3-APPi (10 mg kg-1, s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Tachykinin-induced dyspnea in conscious guinea pigs

Aerosol administration of neurokinin A (NKA) or substance P (SP) to conscious guinea pigs produced labored abdominal breathing (dydpnea). Time to onset of dyspnea was inversely related to tachykinin concentration. Aerosol administration of the neutral endopeptidase inhibitor thiorphan significantly potentiated tachykinin-induced without affecting responses to leukotriene D₄ (LTD₄), carbachol, histamine, platelet activating factor or serotonin (5-HT), indicating selectivity for tachykinins rather than a nonspecific effect on agonist reactivity. The rank order of potency for producing dyspnea was LTD _{NKA (with thiorphan) SP (with thiorphan) > 5-HT = carbachol > histamine > platelet-activating} factor. Pretreatment with propranol, phentolamine, methysergide, pyrilamine or the peptide leukotriene antagonist, ICI 198,165, did not alter dyspnea induced by NKA or SP. The dose-response curves for NKA and SP were shifted to small degrees (< 3-fold) to the right by atropine and to the left by indomethacin. Also, pretreatment with capsaicin did not affect responses to NKA or SP, indicating that they do not cause dyspnea by activating capsaicin sensitive C-fibers. These results suggest primarily direct effects of NKA and SP. This model may be useful for in vivo evaluation of tachykinin antagonists.     

芳香新塔花对大鼠急性心肌缺血和乳鼠心肌细胞的保护作用

目的比较芳香新塔花Ziziphora clinopodioides不同提取物对大鼠急性心肌缺血、对乳鼠心肌细胞缺氧-复氧损伤的影响。方法通过体内注射垂体后叶素造成大鼠急性心肌缺血模型,观察急性心肌缺血大鼠Ⅱ导联心电图J点的变化,以及试药对超氧化物歧化酶(SOD)、乳酸脱氢酶(LDH)、丙二醛(MDA)的影响。体外培养原代SD乳鼠心肌细胞,建立心肌细胞缺氧-复氧损伤模型,用MTT法测定药物对心肌细胞存活率的影响,测定给药后MDA的变化。结果芳香新塔花石油醚部位和氯仿部位0.3g/kg显著抑制注射垂体后叶素所致心电图J点升高,对心率、SOD、LDH、MDA的影响不显著;乙醇提取物和氯仿部位能明显降低缺氧-复氧模型下心肌细胞培养液中的MDA浓度。结论芳香新塔花具有潜在的心肌缺血保护作用。     

咳停片对豚鼠咳嗽反射的抑制作用及析方研究

目的：观察咳停片的镇咳作用，进行初步析方研究。评价该处方的配伍合理性。方法：分复方组（咳停片）、无氯组（不含氯化铵的咳停片）和氯化铵组3组，比较3组对枸橼酸雾化吸入或电刺激喉上神经引起的豚鼠咳嗽反射的抑制作用。结果：复方组和氯化铵组能抑制枸橼酸引起的豚鼠咳嗽反射，复方组的作用强度是氯化铵组的1.32倍，是无氯组4倍以上，无氯组无明显作用。复方组，无氯组能抑制电刺激喉上神经引起的豚鼠咳嗽反射，复方组的作用强度是无氯组的2.94倍。氯化铵组无作用。结论：咳停片处方中剔除氯化铵后镇咳作用减弱，表明氯化铵与处方中的中药成分有协同作用。初步证明了该处方的合理性。     

Naringin attenuates enhanced cough, airway hyperresponsiveness and airway inflammation in a guinea pig model of chronic bronchitis induced by cigarette smoke

Naringin is a flavanone with various bioactivities including expectorant effect, antitussive effect and inhibitory effects on asthma and acute lung injury. In present study we examined the effects of naringin on enhanced cough, airway hyperresponsiveness (AHR) and airway inflammation in chronic cigarette smoke (CS) exposure-induced chronic bronchitis in guinea pigs. To achieve this, guinea pigs were exposed to CS for 8weeks (10cigarettes/day, 6days/week). Oral administration of naringin (9.2, 18.4 and 36.8mg/kg) significantly attenuated the enhanced cough and AHR in smoke-exposed guinea pigs, reduced the concentrations of interleukin-8 (IL-8), leukotriene B4 (LTB4) and tumor necrosis factor-α (TNF-α) in bronchoalveolar lavage fluid (BALF) and decreased the myeloperoxidase (MPO) activity in both BALF and lung tissue, but did not significantly decrease the leukocytes in BALF. Naringin also improved superoxidase dismutase (SOD) activity in lung tissue and increased the content of lipoxin A4 (LXA4) in BALF in this guinea pig model of chronic bronchitis. These results suggested that naringin exhibited antitussive, anti-AHR and anti-inflammation effects on chronic CS exposure-induced chronic bronchitis in guinea pigs, and may possess novel therapeutic potential in the treatment of chronic bronchitis.     

Cough Threshold for Capsaicin Increases by Azelastine in Patients with Cough-variant Asthma

To assess the effects of azelastine in patients with cough-variant asthma, we measured the cough threshold for capsaicin (the concentration required to elicit more than five coughs) in 16 patients with cough-variant asthma before and after 4 weeks of treatment with azelastine (2 mg; b.i.d.) or placebo. After treatment, coughing decreased in all patients and the cough threshold for capsaicin increased significantly, from 0.67±0.30 μmto 4.76±1.55 μm(P<0.01) in the azelastine group. However, the cough threshold for capsaicin did not increase significantly, from 0.86±0.33 μmto 1.11±0.35 μm(P>0.10) in the placebo group. These results suggest that azelastine inhibits coughing in patients with cough-variant asthma.     

Effects of inhaled alpha 2-adrenoceptor and GABAB receptor agonists on citric acid-induced cough and tidal volume changes in guinea pigs.

The effects of alpha 2-adrenoceptor and GABA receptor agonists on citric acid-induced cough and increased tidal volume were investigated in conscious guinea pigs. Inhalation of low doses of B-HT 920 (5-allyl-2-amino 5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepine dihydrochloride), and xylazine significantly inhibited citric acid-induced cough and tidal volume increases. Intraperitoneal administration of higher doses of B-HT 920 than those given by aerosol were ineffective. The inhibitory effects of B-HT 920 were antagonised by prior intraperitoneal administration of yohimbine, but not atropine. Inhalation of GABA or baclofen inhibited tidal volume increases, but had no effect on cough. Inhaled alpha 2-adrenoceptor or GABA agonists had no effect on the reduced respiratory rate after citric acid inhalation. It is concluded that alpha 2-adrenoceptor agonists inhibit cough via a mechanism which may not be related to their ability to reduce citric acid-induced tidal volume increases, since GABA and baclofen inhibited tidal volume increases but not cough. We suggest that alpha 2-adrenoceptor agonists may have therapeutic potential in the treatment of cough.     

Augmentation of spontaneous cough by enalapril through up-regulation of bradykinin B1 receptors in guinea pigs

Studies of angiotensin-converting enzyme inhibitor-induced cough have involved extensive use of experimental models in which guinea pigs are exposed to an inhaled stimulus such as capsaicin or citric acid. In the present study, we examined enalapril-induced potentiation of spontaneous cough in guinea pigs, without an inhaled stimulus. Daily oral administration of enalapril (3 mg/kg) for 20 to 30 days enhanced spontaneous cough. This enhancement of cough was inhibited by the bradykinin B(1) receptor antagonist des-Arg(10)-[Leu(9)]kallidin, but not by the bradykinin B(2) receptor antagonist icatibant. The amount of the bradykinin B(1) receptor agonist [3H]des-Arg(10)-kallidin specifically bound to membrane fractions from the trachea and larynx was increased by prolongation of the enalapril treatment, and positively correlated well with coughing frequency. In conclusion, the present results indicate that enalapril-induced cough is mediated by up-regulation of bradykinin B(1) receptors.     

肺清颗粒药效学作用初探

目的研究肺清颗粒镇咳、祛痰、平喘和抗菌作用。方法以小鼠氨水引咳法、小鼠枸橼酸引咳法和豚鼠枸橼酸引咳法观察其镇咳作用;以小鼠酚红排泌法观察其祛痰作用;以豚鼠乙酰胆碱-组胺引喘法和豚鼠离体气管条试验观察其平喘作用;采用抑菌圈测定法观察肺清颗粒的体外抑菌作用。结果肺清颗粒对小鼠氨水引咳具有显著的镇咳作用,对乙酰胆碱-组胺所致的豚鼠哮喘具有显著的平喘作用;对组胺或乙酰胆碱致痉的豚鼠离体气管条有显著的解痉作用;体外对金黄色葡萄球菌、肺炎球菌和肺炎克雷伯菌有一定的抑制作用。结论肺清颗粒对实验动物具有显著的镇咳、祛痰及平喘作用,并具有一定的抗菌作用。     

Capsaicin evokes secretion of nasal fluid and depletes substance P and calcitonin gene-related peptide from the nasal mucosa in the rat.

1. The secretion of nasal fluid was studied in anaesthetized rats after topical application of capsaicin, and of calcitonin gene-related peptide (CGRP) alone or CGRP in combination with substance P (SP). The flow of nasal fluid was stimulated and the secretions collected by a filter paper technique. The concentrations of SP and CGRP in nasal biopsies were determined after topical or systemic administration of capsaicin. 2. Capsaicin (single dose administration) stimulated nasal secretion in a dose-dependent manner. The effect was inhibited by hexamethonium, lignocaine, or by the tachykinin antagonist (D-Pro2, D-Trp7,9)-SP, but not by atropine, or by a combination of the histamine H1-receptor antagonist chlorpheniramine and the H2-receptor antagonist ranitidine. 3. When applied cumulatively, capsaicin rapidly produced desensitization. The concentrations of SP and CGRP in the nasal mucosa were reduced by capsaicin 6 days after topical or s.c. administration but not 15 min after topical application of desensitizing doses. 4. CGRP did not stimulate the secretion of nasal fluid and did not alter SP-evoked nasal secretion. 5. The inhibition by hexamethonium of the capsaicin-evoked nasal secretion suggests the involvement of ganglionic reflexes. In addition, the inhibition of the response to capsaicin by (D-Pro2,D-Trp7,9)-SP and lidocaine and the depletion of SP and CGRP after capsaicin indicate the involvement of tachykinin-mediated axon reflexes.     

艾叶油的呼吸系统药理研究Ⅰ,支气管扩张、镇咳和祛痰作用

目的：探讨艾叶油的扩张气道平滑肌,镇咳,祛痰作用及机制。方法：采用哮喘发作潜伏期,肺机械功能及离体气管平滑肌松弛试验,观察艾叶油的支气管扩张作用;用豚鼠枸橼酸引咳法和小鼠气道酚红排泄法观察艾叶油的镇咳祛痰作用。     

Substance P as a potent stimulator of sneeze responses in experimental allergic rhinitis of guinea pigs.

Substance P was examined for sneeze-inducing activity and its involvement of sneeze responses in experimental allergic rhinitis. Substance P, dripped into a nostril of guinea pigs, at concentrations of 100 pM and above induced sneezing in a dose-dependent fashion. The activity of substance P was not affected by the previous subcutaneous injections of capsaicin that depleted substance P in nerve fibers. Histamine induced sneezing at concentrations of 30 mM and above and the activity was reduced by capsaicin treatment. The frequency of antigen-induced sneezing was proportional to the substance P content in nasal mucosa of sensitized guinea pigs treated with increasing doses of capsaicin; correlation coefficient 0.91. These results suggest that substance P plays an important role as a stimulator of sneeze responses in experimental allergic rhinitis in guinea pigs.     

Effect of cysteamine on vocalization responses by arterial algogenics in guinea pigs

Effects of cysteamine (2-mercaptoethylamine) on vocalization responses, a parameter of nociceptive response, was studied in conscious guinea pigs. Intra-arterial injection of bradykinin (3 micrograms), acetylcholine (300 micrograms), capsaicin (3 micrograms) and vanillyl n-nonoylamide (3 micrograms, VNA) induced severe vocalization responses. Three hours after an administration of cysteamine (300 mg/kg, s.c.), a significant suppressive effect was observed for bradykinin and acetylcholine-evoked vocalization. A weak suppressive effect appeared in capsaicin and VNA-evoked vocalization, but there were not statistically significant changes on vocalization counts when compared with the value of the saline-treated animals. However, consecutive pretreatment of guinea pigs with VNA led to a complete suppression of capsaicinoids-evoked vocalization only. Cysteamine completely suppressed bradykinin, acetylcholine, capsaicin and VNA-evoked vocalization responses in VNA desensitized guinea pigs. These findings suggest that the mechanisms of bradykinin and acetylcholine-evoked vocalization response differ from that of capsaicinoids.     

Identification of some benproperine metabolites in humans and investigation of their antitussive effect

AIM: To identify 4 unknown metabolites of benproperine (BPP, 1) in human urine after a po dose, and to investigate the antitussive effect of monohydroxylate metabolites. METHODS: The putative metabolite references were prepared using chemical synthesis. Their structures were identified using 1H and 13C nuclear magnetic resonance, and mass spectrometry. The metabolites in human urine were separated and assayed using liquid chromatography-ion trap mass spectrometry (LC/MS/MS), and further confirmed by comparison of their mass spectra and chromatographic retention times with those of synthesized reference substances. The antitussive effects of metabolites were evaluated on coughs induced by 7.5% citric acid in conscious guinea pigs. RESULTS: 1-[1-Methyl-2-[2-(phenylmethyl)phenoxy]-ethyl]-4-piperidinol (2), 1-[1-methyl-2-[2-(phenylmethyl)phenoxy] ethyl]-3-piperidinol (3) and their glucuronides 4 and 5 were obtained from chemical synthesis. Four urinary metabolites in human urine showed peaks with the same chromatographic retention times and mass spectra in LC/MS/MS as synthetic substances 2, 3, 4 and 5. Phosphates of compounds 2 and 3 prolonged the latency of cough and reduced the number of coughs during the 3 min test using citric acid, but did not reduce the number of coughs during the 5 min immediately after the test in conscious guinea pigs. CONCLUSION: Compounds 2, 3, 4, and 5 were identified as the metabolites of BPP in human urine. Among them, compounds 2 and 3 are inactive in the antitussive effect.     

Antitussive effect of RU-20201--central and peripheral actions

The antitussive effect of the new compound 1, 2, 3, 4a, 9b-hexahydro-8, 9b-dimethyl-4-[3-(4-methyl-piperazine-1-yl) propionamide] dibenzofuran-3-one dihydrochloride (RU-20201) was investigated in dogs and guinea pigs, including its sites of action. The antitussive effect of RU-20201 was about 1/10 as potent as that of codeine phosphate in dogs with the puncture electrode-induced cough (PEC) method and about 1/12 and 1/4 as potent as that of codeine phosphate in guinea pigs with the PEC and chemical stimulation methods, respectively. When RU-20201 was administered in a dose range of 1 to 10 mg into the vertebral artery toward the brain in lightly anesthetized dogs, no antitussive effect was observed against the coughing elicited by electrical stimulation of the central cut end of the superior laryngeal nerve. However, a stimulative effect on respiration, especially on respiratory rate occurred. The peripheral effect of RU-20201 on the cough was investigated using the in situ upper trachea perfusion preparation which allows a direct drug administration to the local site around the tracheal mucosa, this site being electrically stimulated to induce coughing. A close i.a. infusion of RU-20201 in doses of 1 and 3 mg/min into the tracheal vascular bed for 5 min inhibited the cough response elicited by mucosal stimulation. The above findings suggest that RU-20201 has a significant antitussive activity, the site of action being probably, at least, at the cough receptor level.