Lack of a role for bradykinin in inhaled sodium metabisulphite-induced airway microvascular leakage in guinea pigs

We have investigated the role of bradykinin in airway microvascular leakage and bronchoconstriction induced by inhaled sodium metabisulphite (MBS) in guinea pigs. A selective bradykinin B2 receptor antagonist, HOE 140 (D-Arg[Hyp³, Thi⁵, D-Tic⁷, Oic⁸]-bradykinin), was used because this drug has been shown to abolish the airway responses induced by bradykinin. Lung resistance (R_L) was measured for 6 min after challenge with MBS, followed by measurement of extravasation of Evans Blue dye into airway tissues, used as an index of plasma exudation. Aerosolized MBS (40 and 80 mmol/L, 30 breaths) induced a significant increase in R_L and leakage of dye in the trachea, main bronchi and intrapulmonary airways, whereas 20 mmol/L MBS caused these responses except for the dye leakage in the trachea and main bronchi. HOE 140 (100 nmol/kg iv) had no effect against these airway responses. We conclude that bradykinin-mediated mechanisms do not play a significant role in the acute airway effects induced by inhaled MBS.     

Differential effects of phosphoramidon on neurokinin A- and substance P-induced airflow obstruction and airway microvascular leakage in guinea-pig.

1. The effects of the inhaled neuropeptides, neurokinin A (NKA) and substance P (SP) on lung resistance (RL) and airway microvascular permeability were studied in anaesthetized guinea-pigs. 2. Single doses of inhaled NKA (3 x 10(-5), 1 x 10(-4), 3 x 10(-4) M; 45 breaths) and SP (1 x 10(-4), 3 x 10(-4), 1 x 10(-3); 45 breaths) caused a dose-dependent increase in both RL and airway microvascular leakage, assessed as extravasation of the albumin marker, Evans blue dye. 3. NKA at 1 x 10(-4) and 3 x 10(-4) M resulted in a significantly higher increase in RL than SP at the same doses. 4. Inhaled SP (3 x 10(-4) M; 45 breaths) caused significantly higher Evans blue dye extravasation in main bronchi and proximal intrapulmonary airways compared to the same dose of NKA. 5. Pretreatment with the specific inhibitor of neural endopeptidase (NEP24.11), phosphoramidon, caused an approximately 100 fold leftward shift of the RL responses to inhaled NKA and SP. 6. Phosphoramidon significantly potentiated both NKA- and SP-induced airway microvascular leakage at proximal intrapulmonary airways, but not at any other airway level. 7. Inhibition of NEP24.11 potentiate both the SP- or NKA-induced airflow obstruction to a larger extent than the induced airway microvascular leakage, suggesting that NEP24.11 is more important in the modulation of the airflow obstruction observed after these mediators.     

Nedocromil sodium inhibits airway hyperresponsiveness and eosinophilic infiltration induced by repeated antigen challenge in guinea-pigs.

1. Repeated exposure to ovalbumin aerosol produced significant increases in epithelial eosinophils of airways of all sizes and produced increased pulmonary resistance (RL) to inhaled acetylcholine (ACh) in guinea-pigs. 2. Nedocromil sodium 10 mg ml-1, by nebulization prior to each ovalbumin (OA) challenge inhibited both the airway eosinophilia and hyperresponsiveness to ACh. 3. Nedocromil sodium pretreatment (10 mg ml-1 by nebulization) 10 min prior to OA completely inhibited the acute bronchoconstrictor response to OA. 4. Our findings suggest that nedocromil sodium inhibits airway hyperresponsiveness by inhibiting eosinophilic infiltration, or by simultaneously inhibiting mechanisms involved in both processes.     

BradykMn-induced airway microvasciilar leakage is potentiated by captopril and phosphoramidon

Bradykinin can be inactivated by the peptidases angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP), both of which are present in the airways. We evaluated the role of these enzymes in bradykinin-induced airway microvascular leakage and lung resistance in anesthetized and mechanically ventilated guinea pigs. We studied the effects of captopril (inhaled; 350 nmol), a specific ACE inhibitor, and phosphoramidon (inhaled; 7.5 nmol), a specific NEP inhibitor. Airway microvascular leakage was measured with the albumin marker Evans Blue dye (20 mg/kg i.v.), and airflow obstruction was measured as lung resistance (R_L). Bradykinin was given by inhalation (0.1, 0.3 and 1 mM; 45 breaths), and caused a dose-dependent increase in both R_L and airway microvascular leakage. Inhibition of NEP or ACE potentiated the bradykinin-induced microvascular leakage in main bronchi and proximal and distal intrapulmonary airways. However, only NEP inhibition significantly potentiated the extravasation of Evans Blue dye into the tracheal wall and lumen. The combined inhibition of NEP and ACE significantly potentiated plasma leakage at all airway levels, as well as the increase in R_L induced by inhaled bradykinin. Recovery R_L after one lung inflation significantly correlated with the extravasation of Evans Blue dye in the tissue at all airway levels, indicating that airway edema may have contributed to airway narrowing. We conclude that in the guinea pig, both NEP and ACE modulate bradykinin-induced airway microvascular leakage.     

Involvement of inflammatory mediators in the airway responses to trimellitic anhydride in sensitized guinea-pigs.

1. We examined the effect of various pharmacological agents on the acute bronchoconstrictor response and airway microvascular leakage in a model of guinea-pig sensitization to trimellitic anhydride (TMA) a cause of low molecular weight occupational asthma in man. 2. Guinea-pigs were given intradermal injections of 0.1 ml of 0.3% TMA in corn oil; 21-28 days later, anaesthetized guinea-pigs were challenged with TMA conjugated to guinea-pig albumin by tracheal instillation. Changes in lung resistance were measured and airway microvascular leakage was quantified by measuring the extravasation of Evans blue dye into the airway tissue. 3. Sensitized guinea-pig (n = 9 in each group) were pretreated with chlorpheniramine (2.5 mg kg-1, i.v.), WEB 2086 (10 micrograms kg-1, i.v.), BW 4AC (50 mg kg-1, i.p.), nedocromil sodium (2% aerosol for 60 s) or vehicle alone. 4. Pretreatment with chlorpheniramine inhibited both the acute bronchoconstrictor response and the increase in airway microvascular leakage. WEB 2086 and nedocromil sodium partially inhibited the bronchoconstrictor response but had no significant effect on airway microvascular leakage. BW 4AC caused a non-significant reduction of the bronchoconstrictor response and airway microvascular leakage. 5. These results indicate that both the bronchoconstrictor response and the airway microvascular response in this model of sensitization is mediated to a large extent by histamine. PAF but not 5-lipoxygenase products also partially mediates the bronchoconstrictor response but not the airway microvascular leakage. Nedocromil sodium partially inhibits the bronchoconstrictor response only.     

Effect of Hoe 140, a new bradykinin receptor antagonist, on bradykinin- and platelet-activating factor-induced bronchoconstriction and airway microvascular leakage in guinea pig.

We have investigated the effect of a new bradykinin receptor antagonist, Hoe 140 (D-Arg- Hyp3,Thi5,D-Tic7,Oic8]-bradykinin), on bradykinin- and platelet-activating factor (PAF)-induced bronchoconstriction and airway microvascular leakage in anesthetized guinea pigs. Extravasation of Evans blue dye and lung resistance were measured simultaneously. Both i.v. (15 nmol/kg) and inhaled bradykinin (1 mM, 45 breaths) caused a significant increase in lung resistance and leakage of dye at all airway levels. Hoe 140 (100 nmol/kg i.v.) almost completely inhibited these airway responses induced by bradykinin except for dye extravasation in trachea induced by inhaled bradykinin. Inhaled PAF (3 mM, 30 breaths) significantly increased lung resistance and leakage of due at all airway levels, but Hoe 140 had no effect on these responses. Bradykinin-induced bronchoconstriction and airway microvascular leakage are predominantly mediated by activation of B2 receptor, since Hoe 140 is a B2 receptor antagonist. Bradykinin receptor-mediated mechanisms do not play an important role on inhaled PAF-induced bronchoconstriction and microvascular leakage.     

Attenuation of tachykinin-induced airflow obstruction and microvascular leakage in immature airways.

1. To study the effect of maturation on substance P (SP)- and neurokinin A (NKA)-induced airflow obstruction and airway microvascular leakage (MVL), we have measured changes in both lung resistance (RL) and extravasation of Evans blue dye in anaesthetized immature (aged 14 +/- 1 days) and adult guinea-pigs (aged 80 +/- 3 days). 2. RL and its recovery after hyperinflation at 5 min were measured for 6 min after i.v. SP (0.2, 1 and 30 nmol kg-1), NKA (1 and 10 nmol kg-1) or vehicle (0.9% NaCl). After measurement of RL, MVL in trachea, main bronchi and intrapulmonary airways was also examined. 3. The order of potency in inducing airflow obstruction did not change with age (NKA > SP) but immature animals required a larger dose of SP or NKA than adults to cause a significant increase in RL. 4. The order of potency in inducing airway microvascular leakage was SP > NKA in both immature and adult animals. The amount of extravasated dye after SP was significantly less in immature airways, especially in central airways. 5. Phosphoramidon (2.5 mg kg-1), a neutral endopeptidase (NEP) inhibitor, significantly increased RL after 0.2 nmol kg-1 SP only in adult airways. Phosphoramidon enhanced the dye extravasation after 0.2 nmol kg-1 SP in both immature and adult airways with a significantly greater amount of dye in adult animals, suggesting that mechanisms other than changes in NEP activity may be responsible for this age-related difference.(ABSTRACT TRUNCATED AT 250 WORDS)     

速激肽受体拮抗剂抗豚鼠过敏性哮喘的作用

实验目的是研究速激肽与哮喘的关系,评价速激肽受体拮抗剂对哮喘的治疗作用。结果表明,ip速激肽NK-1受体拮抗剂CP-96345,NK- 2受体拮抗剂SR-48968或两药合用,均可有效减少清醒致敏豚鼠吸入抗原引起的喘息反应,降低过敏性休克死亡率。SR-48968减轻麻醉豚鼠抗原引起的气道收缩,并浓度依赖性降低抗原引起的气管和支气管平滑肌收缩幅度。CP-96345可抑制抗原诱导的支气管和肺叶伊文思蓝渗出,仅对支气管平滑肌收缩有部分抑制作用。结果提示,速激肽参与哮喘发病,速激肽受体拮抗剂可抑制抗原诱导的气道平滑肌收缩(NK-2受体)和微血管渗漏(NK-1受体)而减轻哮喘反应。     

Evidence for reduction of bradykinin-induced bronchoconstriction in guinea-pigs by release of nitric oxide.

1. In this study the influence of nitric oxide (NO) on the bronchoconstriction induced by bradykinin in anaesthetized and artifically ventilated guinea-pigs pretreated with atropine was investigated. 2. Aerosol administration of bradykinin (0.1-1 mM, 40 breaths) caused a dose-dependent increase in lung resistance (RL): maximum increase in RL was 2.5 fold the baseline value. Pretreatment with aerosolized NG-nitro-L-arginine methyl ester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA) (1 mM, 10 breaths every 5 min for 30 min), NO synthase inhibitors, markedly increased the bronchoconstrictor response to bradykinin. L-Arginine, but not D-arginine, (3 mM, 10 breaths every 5 min for 30 min) reversed the hyperresponsiveness to aerosolized bradykinin caused by L-NAME and L-NMMA. 3. L-NAME (1 mM, 10 breaths every 5 min for 30 min) increased the bronchoconstriction induced by intravenous bradykinin (1-10 nmol kg-1). L-Arginine, but not D-arginine, (10 breaths every 5 min for 30 min) reversed the hyperresponsiveness to intravenous bradykinin caused by L-NAME. 4. The increase in RL induced by capsaicin, either aerosol (10 microM, 10 breaths) or i.v. (20 nmol kg-1) was not affected by L-NAME (1 mM, 10 breaths every 5 min for 30 min). Acute resection of the vagi did not affect the bronchoconstriction evoked by bradykinin in guinea-pigs, either in the absence or presence of L-NAME (1 mM, 10 breaths every 5 min for 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of nedocromil sodium on allergen-, PAF-, histamine- and bradykinin-induced airways vasodilatation and pulmonary obstruction in the pig.

1. The influence of nedocromil sodium on the nasal and bronchial effects induced by allergen, platelet-activating factor (PAF), capsaicin, histamine and bradykinin aerosol challenge in ascaris-sensitized and pentobarbitone-anaesthetized pigs was studied. Blood flow changes in the bronchial and nasal circulation were measured with ultrasonic flow probes around the supplying arteries, and vascular resistance was calculated. Changes in pulmonary resistance (Rpulm), dynamic compliance (Cdyn), mean arterial pressure (MAP) and heart rate (HR) were also determined. 2. Allergen and PAF aerosol challenge in the lung produced similar effects consisting of both bronchial and nasal vasodilatation, bronchoconstriction (increase in Rpulm and decrease in Cdyn) and increases in MAP and HR. Local pretreatment with nedocromil sodium (80 mg, aerosol) reduced the peak and duration of both the bronchial vasodilatation and increase in Rpulm, while only the duration of the change in Cdyn was significantly decreased. Nedocromil sodium did not alter the increases in MAP and HR. The nasal vasodilatation evoked by PAF, but not allergen, challenge in the lung was reduced by nedocromil sodium. 3. Allergen challenge in the nose induced vasodilatation of long duration which was reduced by local nedocromil sodium pretreatment (50 micrograms kg-1, intra-arterially). 4. The vasodilator response to histamine aerosol was attenuated in the nasal, but not the bronchial circulation by local nedocromil sodium pretreatment. Histamine-induced bronchoconstriction was not altered by nedocromil sodium. 5. Bradykinin aerosol-induced vasodilatation in the nasal and bronchial circulation was markedly and equally reduced by local nedocromil sodium and systemic capsaicin (50 mg kg-1, s.c. 2 days before) pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Capsaicin-induced bronchoconstriction in the guinea-pig: contribution of vagal cholinergic reflexes, local axon reflexes and their modulation by BW443C81.

1 The objective of the study was to investigate the central vagal and local axon reflex components of bronchoconstrictor responses evoked by inhalation of capsaicin aerosol in anaesthetized guinea-pigs. This was accomplished by comparing the effects of bilateral vagotomy, atropine and the peripherally-acting polar enkephalin analogue, BW443C81, on bronchoconstrictor responses evoked by capsaicin. The effects of codeine were also determined. 2 Aerosols of capsaicin were generated from a 0.9 microgram ml-1 solution. Inhalation of capsaicin aerosol in 5, 10 and 15 breaths evoked dose-related bronchoconstrictor responses. The responses were immediate in onset and of extended duration. 3 Capsaicin-induced bronchoconstrictor responses were significantly inhibited following bilateral vagotomy or atropine (0.3 mg kg-1, i.v.) pretreatment by 46% +/- 14% (P less than 0.05) and 59% +/- 13% (P less than 0.01), respectively. 4 Administration of BW443C81 by intravenous infusion (3, 30 and 100 micrograms kg-1 min-1) caused a significant inhibition of capsaicin-induced bronchoconstrictor responses which achieved a greater maximum than either bilateral vagotomy or atropine. Codeine (100 micrograms kg-1 min-1, i.v.) did not significantly inhibit the bronchoconstrictor responses. 5 Inhibition of capsaicin-induced bronchoconstrictor responses by BW443C81 (30 micrograms kg-1 min-1, i.v.) was significantly (P less than 0.05) reduced by the peripherally-acting opioid antagonist N-methyl nalorphine (100 micrograms kg-1 min-1, i.v.). 6 These results show that capsaicin-induced bronchoconstrictor responses are mediated by at least two mechanisms, a vagal and/or cholinergic reflex pathway and a non-cholinergic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of respiratory manoeuvres and pharmacological agents on the pharmacokinetics of nedocromil sodium after inhalation.

1. Eight healthy subjects inhaled nedocromil sodium from a metered-dose inhaler using a standardised inspiratory technique. Blood samples were taken for up to 270 min after inhalation for radioimmunoassay of plasma nedocromil sodium concentrations. 2. To investigate the possibility that respiratory manoeuvres can alter the absorption of the drug from the lungs, on the first (control) study day at 70 min after dosing, subjects performed nine forced expiratory manoeuvres over a 3 min period. At 110 min after dosing, subjects took a slow, full inspiration with a 30 s breath-hold, and at 150 min after dosing the subjects performed one single forced expiration. 3. On the second study day, subjects inhaled methoxamine, 0.15 mg kg-1 of a 20 mg ml-1 solution at 60 min after dosing, and the study continued as above. On the third day, subjects repeated the sequence of respiratory manoeuvres, after having taken phenoxymethyl penicillin and probenecid by mouth for 48 h. 4. Both multiple forced expirations and the deep inspiration with breath-hold produced significant increases in the absorption of nedocromil sodium. Inhaled methoxamine did not alter airway calibre or the response to the respiratory manoeuvres. Probenecid, but not penicillin, was detected in the subjects' plasma, and had the effect of increasing the rise in plasma nedocromil sodium concentrations after the multiple forced expirations when compared with the control day. 5. These data suggest that disruption of epithelial tight junctions induced by the respiratory manoeuvres leads to enhanced paracellular transport of nedocromil sodium into the draining circulation of the airways and alveoli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of substance P-induced microvascular leakage by inhaled methoxamine in rat airways.

1. The effect of the inhaled alpha-adrenoceptor agonist, methoxamine (MTX), was studied on experimental airway oedema induced by injection of substance P (SP) in the rat. Sprague-Dawley rats (300-350 g) were anaesthetized with sodium thiopentone, tracheotomized and artificially ventilated. 2. MTX or its vehicle was administered by inhalation. Airway resistance and blood pressure were monitored continuously. Evans Blue dye (EB, 20 mg kg-1) was injected through a jugular catheter 1 min before SP (14.8 nmol kg-1). Airways were dissected out, weighed and placed in formamide for EB extraction and determination by spectrophotometry. 3. EB extravasation induced by SP was significantly reduced in distal intraparenchymal bronchi by inhaled MTX at doses of 50 micrograms kg-1 (58 +/- 9 vs 96 +/- 9 ng EB mg-1 tissue after vehicle, P < 0.001) and 100 micrograms kg-1 (69 +/- 11 vs 137 +/- 26 ng EB mg-1 tissue after vehicle, P < 0.01). Inhaled MTX by itself (100 micrograms kg-1) increased blood pressure: 172 +/- 6 vs 132 +/- 10 mmHg baseline (P < 0.02), but neither induced extravasation nor increased airway resistance. 4. In another set of experiments without SP, MTX was administered intravenously 1 min after EB. At 100 micrograms kg-1, i.v. MTX increased blood pressure to a similar extent as inhaled MTX (180 vs 147 mmHg baseline, P < 0.01), increased airway resistance and caused leakage of plasma proteins in distal intraparenchymal bronchi (79 +/- 7 vs 47 +/- 1 ng EB mg-1 tissue, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Alteration in airway microvascular leakage induced by sensorineural stimulation in rats exposed to inhaled formaldehyde

Inhaled formaldehyde can rapidly produce microvascular leakage in the airway through stimulation of tachykinin NK1 receptors by tachykinins released from sensory nerves. Tachykinin NK1 receptors are known to be internalized in the cytoplasm after being stimulated, thus leading to transient attenuation of their action. We investigated time changes in airway microvascular leakage during formaldehyde inhalation for 45 min, and whether pre-inhalation of formaldehyde (5 ppm, 30 min) decreases the responses induced by subsequent inhaled formaldehyde (5 ppm, 15 min), intravenous capsaicin (75 μg/kg) and intravenous substance P (10 μg/kg) in rat airway. Evans blue dye content extravasated into the tissues was measured as an index of plasma leakage. Formaldehyde rapidly produced dye leakage in the airway, a response that ended within 15 min after the start of formaldehyde inhalation. Pre-inhalation of formaldehyde markedly decreased the responses induced by formaldehyde and capsaicin, but not substance P. However, dye leakage induced by formaldehyde was significantly enhanced by formaldehyde inhalation 20 h earlier. Our results suggest that tachyphylaxis in neurogenic airway microvascular leakage seen after formaldehyde inhalation may be due to impairment of tachykinin release from sensory nerves or decreases in tachykinins within sensory nerves. However, desensitization of tachykinin NK1 receptors was unlikely to be important in the tachyphylactic response.     

Neurogenic airway microvascular leakage induced by toluene inhalation in rats

Toluene is a representative airborne occupational and domestic pollutant that causes eye and respiratory tract irritation. We investigated whether a single inhalation of toluene elicits microvascular leakage in the rat airway. We also evaluated the effects of CP-99,994, a tachykinin NK(1) receptor antagonist, and ketotifen, a histamine H1 receptor antagonist with mast cell-stabilizing properties, on the airway response. The content of Evans blue dye that extravasated into the tissues was measured as an index of plasma leakage. Toluene (18-450 ppm, 10 min) concentration-dependently induced dye leakage into the trachea and main bronchi of anesthetized and mechanically ventilated rats. Toluene at concentrations of ≥ 50 and ≥ 30 ppm caused significant responses in the trachea and main bronchi, respectively, which both peaked after exposure to 135 ppm toluene for 10 min. This response was abolished by CP-99,994 (5 mg/kg i.v.), but not by ketotifen (1mg/kg i.v.). Nebulized phosphoramidon (1 mM, 1 min), a neutral endopeptidase 24.11 inhibitor, significantly enhanced the response induced by toluene (135 ppm, 10 min) compared with nebulized 0.9% saline (1 min). These results show that toluene can rapidly increase airway plasma leakage that is predominantly mediated by tachykinins endogenously released from airway sensory nerves. However, mast cell activation might not be important in this airway response.     

Role of kinins in anaphylactic-induced bronchoconstriction mediated by tachykinins in guinea-pigs.

1. In the present study, we have investigated the role of kinins in allergen-induced bronchoconstriction. 2. Anaesthetized guinea-pigs were sensitized to ovalbumin, ventilated artificially, pretreated with atropine (1.4 mumol kg-1, i.v.) and total pulmonary resistance (RL) measured. In preliminary studies in the presence of the neutral endopeptidase inhibitor, phosphoramidon (4.5 mumol kg-1, i.v.), the bradykinin B2 receptor antagonist Hoe 140 (0.1 mumol kg-1, i.v.) completely abolished the increase in RL following aerosolized bradykinin (1 mM, 40 breaths), but had no effect on the increase in RL following aerosolized neurokinin A (NKA, 10 microM, 40 breaths). On the other hand, a combination of the NK1 (CP-96,345, 2 mumol kg-1, i.v.) and NK2 (SR 48968, 0.3 mumol kg-1, i.v.) tachykinin receptor antagonists abolished completely the increase in RL produced by NKA and partially inhibited the increase in RL produced by bradykinin. These results confirm previous studies that suggest that bradykinin induces the release of tachykinins from sensory nerves in guinea-pig airways. 3. Aerosolized ovalbumin (0.5%, 5 breaths) increased RL in sensitized guinea-pigs pretreated with atropine (1.4 mmol kg-1, i.v.), an effect that began within 2 min and reached a maximum within 5 min; RL remained above baseline at 20 min. Pretreatment with the bradykinin B2 receptor antagonist, Hoe 140, decreased the bronchoconstrictor effect of ovalbumin markedly at 10 to 20 min. In the presence of phosphoramidon (4.5 mumol kg-1, i.v.) the inhibition induced by Hoe 140 was apparent earlier and remained over the 20 min period of study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nociceptin inhibits airway microvascular leakage induced by HCl intra-oesophageal instillation

1. Gastro-oesophageal acid reflux may cause airway responses such as cough, bronchoconstriction and inflammation in asthmatic patients. Our previous results suggest that microvascular leakage induced, in the guinea-pig airways, by intra-oesophageal hydrochloric acid (HCl) infusion was mainly dependent on the release of tachykinins. Nociceptin, an endogenous ligand of the opioid receptor NOP, has been shown to inhibit bronchoconstriction and cough in guinea-pig or cat by inhibiting tachykinin release. 2. The purpose of this study was to investigate the effects of nociceptin on the intra-oesophageal HCl-induced airway microvascular leakage evaluated by Evans blue dye extravasation measurement in anaesthetised guinea-pigs pretreated with propranolol, atropine and phosphoramidon. 3. Infusion of intra-oesophageal HCl led to a significant increase in plasma extravasation in the main bronchi and trachea. This increase was abolished when animals underwent a bilateral vagotomy. 4. Airway microvascular leakage was inhibited by nociceptin (3-30 microg x kg(-1) i.v.) in a dose-dependent manner (maximal inhibition at the dose of 30 microg x kg(-1): 19.76+/-1.13 vs 90.92+/-14.00 ng x mg(-1) tissue for nociceptin and HCl infusion, respectively, in the main bronchi, P<0.01). The NOP receptor agonist [Arg(14),Lys(15)]N/OFQ mimicked the inhibitory effect of nociceptin, but at a 10-fold lower dose (3 microg x kg(-1) i.v). The NOP receptor antagonist J-113397 had no effect on plasma protein extravasation by itself, but was able to block the inhibitory effect of nociceptin. 5. Morphine (1 mg x kg(-1)) had a similar inhibitory effect as that of nociceptin. Naloxone pretreatment abolished the effect of morphine, but was enable to block the inhibitory effect of nociceptin. 6. Under similar conditions, nociceptin, in the previous range of concentration, was unable to counteract the airway microvascular leakage induced by substance P (SP). 7. These results suggest that airway plasma extravasation induced by intra-oesophageal HCl instillation might be inhibited by specific stimulation of the NOP receptor with nociceptin. Nociceptin is likely to act at a pre-junctional level, by inhibiting tachykinin release, since it was unable to prevent SP-induced airway plasma extravasation.     

Activation of the nociceptin/orphanin FQ receptor reduces bronchoconstriction and microvascular leakage in a rabbit model of gastroesophageal reflux

1. Nociceptin/orphanin FQ (N/OFQ) is the endogenous peptide ligand for a specific G-protein coupled receptor, the N/OFQ peptide receptor (NOP). The N/OFQ-NOP receptor system has been reported to play an important role in pain, anxiety and appetite regulation. In airways, N/OFQ was found to inhibit the release of tachykinins and the bronchoconstriction and cough provoked by capsaicin. 2. Here we evaluated the effects of NOP receptor activation in bronchoconstriction and airway microvascular leakage induced by intraesophageal (i.oe.) hydrochloric acid (HCl) instillation in rabbits. We also tested the effects of NOP receptor activation in SP-induced plasma extravasation and bronchoconstriction. 3. In anesthetized New Zealand rabbits bronchopulmonary function (total lung resistance (R(L)) and dynamic compliance (C(dyn))) and airway microvascular leakage (extravasation of Evans blue dye) were evaluated. 4. Infusion of i.oe. HCl (1 N) led to a significant increase in bronchoconstriction and plasma extravasation in the main bronchi and trachea of rabbits pretreated with propranolol, atropine and phosphoramidon. 5. Bronchoconstriction and airway microvascular leakage were inhibited by N/OFQ (3-30 microg kg(-1) i.v.) in a dose-dependent manner. The NOP receptor agonist [Arg14,Lys15]N/OFQ mimicked the inhibitory effect of N/OFQ, being 10-fold more potent, UFP-101, a peptide selective NOP receptor antagonist, blocked the inhibitory effects of both agonists. 6. Under the same experimental conditions, N/OFQ and [Arg14,Lys15]N/OFQ did not counteract the bronchoconstriction and airway microvascular leakage induced by substance P. 7. These results suggest that bronchoconstriction and airway plasma extravasation induced by i.oe. HCl instillation are inhibited by activation of prejunctional NOP receptors.     

Modulation of neurally mediated airway microvascular leakage in guinea-pig airways by beta 2-adrenoceptor agonists.

The effect of two beta 2-adrenoceptor agonists, salbutamol (100 micrograms/kg i.v.) and broxaterol (100 micrograms/kg i.v.), on airway microvascular leakage induced by vagal stimulation was studied in anaesthetised guinea pigs. Airway microvascular leakage was measured by Evans blue extravasation. Broxaterol, but not salbutamol, inhibited Evans blue dye extravasation at all airway levels, an effect prevented by pretreatment with propranolol (1 mg/kg). Neither of the beta 2-agonists had any effect on substance P-induced Evans blue dye extravasation. Broxaterol inhibits the prejunctional release of tachykinins from airway sensory nerves by stimulation of beta-receptors. The mechanism by which beta-adrenoceptor agonists prevent airway microvascular leakage deserves further study.     

Effect of an inhaled histamine H3-receptor agonist on airway responses to sodium metabisulphite in asthma.

Histamine H3-receptor agonists inhibit excitatory neuro-transmission in human and guinea-pig airways. Since neural bronchoconstriction may be important in asthma we have studied the effect of a specific H3-receptor agonist R-alpha-methylhistamine (alpha MeHA) on bronchoconstriction induced by the inhaled irritant sodium metabisulphite (MBS) in six mild asthmatic subjects in a randomised double-blind crossover study. Subjects received either alpha MeHA, 10 mg (as a chloride salt) or matched placebo (P) and were then challenged with doubling concentrations of MBS (0.3-80 mg ml-1) nebulised from a dosimeter at 5 min intervals with measurement of specific airway conductance (sGaw) and FEV1 at 2 and 4 min respectively after each inhalation. There was no effect of alpha MeHA on baseline airway calibre and the log concentrations of MBS required to lower sGaw by 50% (log PC50) and FEV1 by 20% (log PC20) were not significantly different after alpha MeHA when compared with placebo, suggesting that selective stimulation of airway H3-receptors does not inhibit MBS-induced bronchoconstriction.