Effect of NZ-107 on late-phase airway responses and airway hyperreactivity in guinea pigs

The effect of NZ-107 (4-bromo-5-(3-ethoxy-4-methoxybenzylamino)-3(2H)-pyridazinone) on late-phase airway responses and airway hyperreactivity was investigated in the guinea pig. Challenge with inhaled ovalbumin in conscious guinea pigs actively sensitized with inhaled ovalbumin caused triphasic bronchial obstruction, which peaked at 5-30 min, 6-8 h and 24 h. In this model, airway hyperreactivity to acetylcholine was observed 48 h after antigen challenge. Orally administered NZ-107, given 2 h before ovalbumin challenge significantly inhibited airway responses at 5-30 min (10 mg/kg), 6-8 h (30 mg/kg), 24 h (10 mg/kg) and airway hyperreactivity (30 mg/kg). When NZ-107 (10 mg/kg) was orally administered to the guinea pigs 3 h after ovalbumin challenge, it also inhibited airway responses at 6-8 h and 24 h and airway hyperreactivity. In anaesthetized guinea pigs, intravenous administration of NZ-107 (0.03-1.0 mg/kg) inhibited platelet-activating factor (PAF)- and propranolol-induced airway hyperreactivity to histamine. These results suggest that NZ-107 may be a useful drug for the treatment of bronchial asthma by reducing late-phase airway responses and airway hyperreactivity.     

Non-specific Airway Hyperreactivity in Isolated Respiratory Preparations from Guinea-pigs Sensitized and Challenged with Ovalbumin

Summary: Airway hyperreactivity to physical, chemical, immunological and pharmacological stimuli is well documented in vivo. The aim of this study was to investigate whether tissues taken from guinea-pigs that had been shown to display hyperreactivity in vivo after antigen challenge were also hyperreactive in vitro. Isolated airway-perfused lungs from ovalbumin-sensitized guinea-pigs challenged 24 h beforehand with an aerosol of ovalbumin showed a significant (P<0.05) increase in responsiveness to the bronchoconstrictor response to a bolus dose of carbachol (10 μg) when compared with saline challenged animals. The contractile responses to single doses of carbachol (10 μg) and histamine (30 μg) in immersed tracheal spiral preparations taken from sensitized animals exposed to the ovalbumin were also significantly enhanced (P<0.05). A non-significant leftward shift was observed in the concentration-response curve for histamine in challenged perfused lungs from ovalbumin-challenged animals compared with an NaCl challenge. Concentration-response curves to carbachol and histamine in immersed tracheal spirals were virtually superimposed. Therefore, this study has shown non-specific airway hyperreactivity of isolated airway perfused lungs at 24 h following a challenge of sensitized gainea-pigs with aerosolized ovalbumin, although this was not evident from concentration-response curves in immersed trachea. The isolated perfused lung therefore provides a simple method for further evaluation of the mechanisms of airway hyperreactivity.     

Effect of sensitization and aerosol antigen challenge in guinea-pigs—studies of airway receptor function and characteristics

Immunological sensitization of guinea-pigs and subsequent antigen inhalation challenge has provided an animal model which has several features in common with human asthma. Impairment of β-adrenoceptor-mediated function and mechanisms have been postulated to contribute to the hyperreactivity to contractile agonists demonstrated in vivo and in vitro in these animals. Functional and receptor radioligand binding studies were carried out on airway tissue from: non-sensitized; sensitized; sensitized saline challenged; sensitized antigen challenged guinea-pigs. Sensitization did not alter responsiveness of airway tissue to carbachol, although subsequent antigen challenge did increase carbachol sensitivity of peripheral airway tissue six-fold. Neither sensitization itself nor subsequent antigen challenge altered binding characteristics of the muscarinic cholinoceptor ligand [³H]quinuclidi-nyl benzilate ([³H]QNB) to peripheral airway tissue, suggesting that mechanisms responsible for increases in carbachol sensitivity are distal to these receptors. Relaxation of airway preparations to isoprenaline was not altered by sensitization or further antigen challenge of the animals. However, sensitization significantly reduced affinity but not the total number of binding sites in peripheral airway tissue for the β-adrenoceptor ligand [³H]dihydroalpreno-lol ([³H]DHA). Antigen challenge of the animals did not further alter β-adrenoceptor ligand binding characteristics. These results suggest that airway hyperreactivity in this model is not a function of alteration in receptor characteristics, or impairment of relaxation mechanisms.     

Repeated aeroallergen challenge induces lung dysfunction but not bronchial hyperresponsiveness in conscious guinea pigs.

Adult male Hartley-strain guinea pigs were sensitized by 10 min exposure to aerosolized 1% ovalbumin (OA; 10 mg/ml in normal saline containing 4% heat-killed B. pertussis vaccine and 0.02% antifoam B emulsion). One week after sensitization, animals were placed in an exposure chamber and challenged (nebulized OA 0.5%) until each animal showed labored breathing. Maximal exposure time was 10 min. Diphenhydramine (20 mg/kg, i.p.) was given 1 h before each OA challenge to protect the animals from bronchospasmic death. Antigen challenge was repeated twice a week for 2 weeks. The specific airway resistance (sR(aw)) changes in response to increasing concentrations of aerosolized acetylcholine (Ach) were determined. The data obtained in this study demonstrated that repeated antigen challenge produced a significant bronchial tone i.e. an increase in sR(aw) and a decline in specific airway conductance (sG(aw)) and failed to induce bronchial hyperreactivity to aerosolized acetylcholine (Ach) in conscious guinea pigs.     

Etanercept prevents airway hyperresponsiveness by protecting neuronal M2 muscarinic receptors in antigen-challenged guinea pigs

Background and purpose

Increased tumour necrosis factor-α (TNF-α) is associated with airway hyperreactivity in antigen-challenged animals. In human asthmatics, TNF-α is increased and blocking it prevents airway hyperreactivity in some asthmatic patients. However, the mechanisms by which TNF-α mediates hyperreactivity are unknown. Airway hyperreactivity can be caused by dysfunction of neuronal M₂ muscarinic receptors that normally limit acetylcholine release from parasympathetic nerves. Here we test whether blocking TNF-α receptors with etanercept prevents M₂ receptor dysfunction and airway hyperreactivity in antigen-challenged guinea pigs.

Experimental approach

Ovalbumin-sensitized guinea pigs were challenged by inhalation of antigen. Some animals received etanercept (3 mg kg⁻¹ i.p.) 3 h before challenge. 24 h after challenge, airway hyperreactivity and M₂ receptor function were tested. Inflammatory cells in bronchoalveolar lavage, blood and lung were counted. TNF-α and its receptors were detected by real-time RT-PCR and immunocytochemistry in parasympathetic nerves from humans and guinea pigs and in human neuroblastoma cells.

Key results

Antigen-challenged animals were hyperreactive to vagal stimulation and neuronal M₂ receptors were dysfunctional. Both M₂ receptor dysfunction and airway hyperreactivity were prevented by etanercept. Etanercept reduced eosinophils around airway nerves, and in blood, bronchoalveolar lavage and airway smooth muscle. Also, TNF-α decreased M₂ receptor mRNA in human and guinea pig parasympathetic neurons.

Conclusions and implications

Tumour necrosis factor-α may contribute to M₂ receptor dysfunction and airway hyperreactivity directly by decreasing receptor expression and indirectly by promoting recruitment of eosinophils, containing major basic protein, an M₂ antagonist. This suggests that etanercept may be beneficial in treatment of allergic asthma.     

Inhibitory effect of 1,8-cineole on guinea-pig airway challenged with ovalbumin involves a preferential action on electromechanical coupling

• 1 1,8‐Cineole is a terpenoid constituent of essential oils with anti‐inflammatory properties. It reduces the neural excitability, functions as an antinociceptive agent and has myorelaxant actions in guinea‐pig airways. The aim of the present study was to investigate the mechanism underlying the myorelaxant effects of 1,8‐cineole in guinea‐pig isolated trachea from either naïve guinea‐pigs or ovalbumin (OVA)‐sensitized animals subjected to antigenic challenge.
• 2 Isometric recordings were made of the tone of isolated tracheal rings. Rings with an intact epithelium relaxed beyond basal tone in the presence of 1,8‐cineole (6.5 × 10^?6 to 2 × 10^?2 mol/L) in a concentration‐dependent manner (P < 0.001, anova ) with a pD₂ value of 2.23 (95% confidence interval 2.10–2.37). Removal of the epithelium or pretreatment of intact tissue for 15 min with 50 µmol/L N^G‐nitro‐l ‐arginine methyl ester, 5 mmol/L tetraethylammonium, 0.5 µmol/L tetrodotoxin or 5 µmol/L propranolol did not alter the potency (pD₂) or the maximal myorelaxant effect (E_max) of 1,8‐cineole.
• 3 1,8‐Cineole also significantly decreased the Schultz‐Dale contraction induced by OVA, mainly in preparations from OVA‐sensitized animals submitted to antigen challenge. 1,8‐Cineole decreased tracheal hyperresponsiveness to KCl and carbachol caused by antigen challenge and almost abolished the concentration–response curves to KCl, whereas it had little effect on the concentration–response curves to carbachol. Under Ca²⁺‐free conditions and in the presence of 10^?4 mol/L acetylcholine, neither 1,8‐cineole (6.5 × 10^?3 mol/L) nor verapamil (1 × 10^?5 mol/L) affected Ca²⁺‐induced contractions, but they almost abolished Ba²⁺‐induced contractions.
• 4 In conclusion, the findings of the present study show that 1,8‐cineole is a tracheal myorelaxant that acts preferentially on contractile responses elicited electromechanically.

     

β-receptors during aging in respiratory tissues

Specific [¹²⁵I]hydroxybenzylpindolol binding (33 fmol/mg protein) was detected in tracheal tissues from middle aged (417g) and old (757 g) guinea pigs binding was not measurable in tracheal tissues from young (118 g) animals. Similarly, receptor density increased in bronchial and parenchymal tissues during development but receptor affinity did not change. For any age, the receptor densities were parenchyma>bronchi>tracheas (20/7/1); receptor affinities were identical. The potency of 1-isoproterenol in relaxing bronchial muscle was reduced during development. In vivo, salbutamol reduced airway reactivity to histamine and was most potent in animals exhibiting airway hyperreactivity. In addition, 1-propranolol sensitized airway muscle to the bronchoconstrictor effects of histamine in young guinea pigs; in old guinea pigs of the same airway reactivity, 1-propranolol did not affect the induced bronchoconstriction. Our data suggest that there is a reduced sensitivity of airway muscle to catecholamines during development which may be due, in part, to increased density of β-adrenoceptors which are not involved in eliciting the physiological response.     

Effect of YM-40461, a novel surfactant secretagogue, on chronic obstructive pulmonary diseases and similar symptoms in guinea pigs

YM-40461 (1-(2-dimethylaminoethyl)-1-(3,4,5-trimethoxyphenyl)urea, CAS 142912-85-4), is a novel surfactant secretagogue. The effect of YM-40461 on symptoms, e.g. change of airway functions and hypoxemia, were examined using guinea pigs with induced subacute bronchitis. Bronchitic guinea pigs exhibited basal lung resistance (RL) was 0.152 +/- 0.005 cm H2O/ml/s (normal: 0.130 +/- 0.002 cm H2O/ml/s) and basal lung compliance (CL) of 0.455 +/- 0.011 ml/cm H2O (normal: 0.509 +/- 0.009 ml/cm H2O). Although YM-40461 slightly improved the lung resistance in these animals, it improved significantly and dose-dependently the lung compliance (0.468 +/- 0.008 ml/cm H2O for 1 mg/kg, 0.477 +/- 0.008 for 3 mg/kg, 0.490 +/- 0.011 for 10 mg/kg, p < 0.05 at 10 mg/kg) compared to nontreated bronchitic guinea pigs. YM-40461 improved airway functions in bronchitic guinea pigs just as wall as the beta 2-adrenoceptor agonist salbutamol. Additionally, YM-40461 significantly reduced airway hyperreactivity in response to intravenously infused acetylcholine (ACh). Basal PaO2 was 83.1 +/- 0.7 cm H2O in healthy guinea pigs and 71.2 +/- 1.7 cm H2O in bronchitic guinea pigs, indicating hypoxemia. A dose of 10 mg/kg of YM-40461 relieved hypoxemia in these animals with the values returning to 81.8 +/- 1.9 cm H2O (p < 0.05). These results suggest that YM-40461 ameliorates chronic obstructive pulmonary disease (COPD)-like symptoms in bronchitis models due to increased surfactant in the airway.     

Effects of inhaled glaucine on pulmonary responses to antigen in sensitized guinea pigs

The alkaloid (S)-(+)-1,2,9,10-tetramethoxyaporphine (glaucine) is a phosphodiesterase 4 inhibitor with bronchodilator and anti-inflammatory activity in vitro. In this study, we examined the in vivo effects of glaucine on an animal model of asthma. In ovalbumin sensitized guinea pigs, inhaled glaucine (10 mg ml(-1), 3 min) inhibited the acute bronchoconstriction produced by aerosol antigen (antigen response was 256+/-42 and 95+/-14 cm H(2)O l(-1) s(-1) in control and glaucine-treated animals, respectively; P<0.05). Pretreatment with glaucine (10 mg ml(-1), 10 min inhalation, 30 min pre- and 3 h post-antigen exposure) markedly reduced airway hyperreactivity to histamine, eosinophil lung accumulation, and increased eosinophil peroxidase activity in bronchoalveolar lavage fluid 24 h after exposure of conscious guinea pigs to aerosol antigen. In addition, inhaled glaucine (5-10 mg ml(-1), 3 min) inhibited the microvascular leakage produced after inhaled antigen at all airway levels. These data support the potential interest of phosphodiesterase 4 inhibitors in asthma treatment.     

Curcumin attenuates allergen-induced airway hyperresponsiveness in sensitized guinea pigs

Anti-asthmatic property of curcumin (diferuloylmethane), a natural product from the rhizomes of Curcuma longa, has been tested in a guinea pig model of airway hyperresponsiveness. We sensitized guinea pigs with ovalbumin (OVA) to develop certain characteristic features of asthma: allergen induced airway constriction and airway hyperreactivity to histamine. Guinea pigs were treated with curcumin during sensitization (to examine its preventive effect) or after developing impaired airways features (to examine its therapeutic effect). Status of airway constriction and airway hyperreactivity were determined by measuring specific airway conductance (SGaw) using a non-invasive technique, constant-volume body plethysmography. Curcumin (20 mg/kg body weight) treatment significantly inhibits OVA-induced airway constriction (p<0.0399) and airway hyperreactivity (p<0.0043). The results demonstrate that curcumin is effective in improving the impaired airways features in the OVA-sensitized guinea pigs.     

Uptake and biotransformation of ibuterol and terbutaline in isolated perfused rat and guinea pig lungs

The lung uptake and biotransformation of [³H]terbutaline and [³H]ibuterol (diisobutyrate ester of terbutaline) was studied using isolated perfused and ventilated rat and guinea pig lungs. The lung extraction ratio, as calculated from the concentration of drug in the inflowing and outflowing medium, in single pass studies of ibuterol ranged from 0.32 to 0.41 at inflowing concentrations 1 × 10^?5 and 1 × 10^?7M and that of terbutaline ranged from 0.013 to 0.021. Ibuterol was hydrolyzed to terbutaline but no further biotransformation of terbutaline was found. The lung clearance of ibuterol (1 × 10^?7M) was estimated to 0.092 ml/sec. When ibuterol (1 × 10^?7M) was infused together with eserine, an esterase inhibitor, the clearance of ibuterol decreased to 0.088 ml/sec (eserine 1 × 10^?5M) and 0.045 ml/sec (eserine 1 × 10^?4M). The latter value was significantly lower (P < 0.001) than control.     

Effects of a new antiallergic drug, VUF-K-8788, on infiltration of lung parenchyma by eosinophils in guinea pigs and eosinophil-adhesion to human umbilical vein endothelial cells (HUVEC)

Airway inflammation and reversible airway obstruction are hallmarks of bronchial asthma. In this study, we investigated the effects of a new antiallergic drug, 7-[3-[4-(2-quinolinylmethyl)-1-piperazinyl]-propoxy]-2,3-dihydro-4H-1,4-benzothiazin-3-one (VUF-K-8788), on histopathological changes in lung parenchyma of guinea pigs during late-phase asthmatic reaction (LAR), and on eosinophil-adhesion to human umbilical vein endothelial cells (HUVEC). Repeated exposure to ovalbumin of sensitized guinea pigs induced inflammatory phenomena such as hyperplasia of airway epithelial cells, perivascular edema and infiltration of lung parenchyma by eosinophils. VUF-K-8788 inhibited these histopathological phenomena at 10 mg/kg p.o. Moreover, the eosinophil-adherence to HUVEC was inhibited by VUF-K-8788 at the concentration of 10-30 microM. In conclusion, this inhibitory effect of VUF-K-8788 on eosinophil-adherence might contribute to the prevention of LAR and infiltration by eosinophils in the experimental asthmatic model in guinea pigs.     

Comparison of the airway hyperreactivity produced by single and multiple antigen exposures in sensitized guinea pigs.

Chronic airway hyperreactivity is a hallmark feature of asthma, but animal models of airway hyperreactivity often utilize a single antigen challenge. Therefore, we compared the airway hyperreactivity produced by single and multiple antigen challenges in ovalbumin-sensitized guinea pigs. Significant (2-fold) leftward shifts in dose-response curves for i.v. methacholine- or LTD4-induced bronchoconstriction in anesthetized and ventilated animals occurred 24 h following a single ovalbumin challenge. This nonspecific airway hyperreactivity was prevented by pretreatment with ketotifen or dexamethasone. However, airway hyperreactivity was no greater 24 h following the last of 3 daily antigen challenges than after 1 challenge and was absent 72 h following one antigen challenge. These results raise concern over the similarity of antigen-induced airway hyperreactivity in guinea pigs to the chronic airway hyperreactivity in asthmatics.     

Neurogenic goblet cell secretion and bronchoconstriction in guinea pigs sensitised to trimellitic anhydride

Trimellitic anhydride is a cause of occupational asthma in humans. We have previously found that tracheal instillation of trimellitic anhydride conjugated to guinea pig serum albumin induces acute bronchoconstriction and airway plasma exudation in sensitised animals, responses mediated primarily via histamine release. In the present study, neural mechanisms mediating bronchoconstriction and goblet cell secretion were determined in trimellitic anhydride-sensitised guinea pigs using the ganglionic blocker hexamethonium to eliminate efferent reflex mechanisms, pretreatment with capsaicin to eliminate afferent mechanisms, or cimetidine and mepyramine to eliminate histamine-mediated mechanisms. The magnitude of secretion of intracellular mucus from tracheal goblet cells was quantified morphometrically as a mucus score which is inversely related to the degree of discharge. Guinea pigs were injected intradermally either with 0.1 ml 0.3% trimellitic anhydride in corn oil or with corn oil alone as control. Fourteen to eighteen days later all sensitised animals had developed specific immunoglobulin (Ig) G1 antibodies whereas the controls had not. Tracheal instillation of conjugated trimellitic anhydride in anaesthitised animals significantly increased airway lung resistance (R_L) 24-fold in sensitised guinea pigs (34.3 ± 7.9 cm H₂O · ml⁻¹ · s) compared with controls (1.4 ± 0.1 cm H₂O · ml⁻¹ · s). Mucus score was significantly reduced by 51% (indicating goblet cell secretion) in sensitised guinea pigs (183 ± 22 mucus score units) compared with controls (372 ± 41 mucus score units). The antihistamines significantly inhibited conjugated trimellitic anhydride-induced bronchoconstriction by 89%, but did not significantly affect goblet cell discharge. Hexamethonium alone did not significantly affect conjugated trimellitic anhydride-induced bronchoconstriction or goblet cell secretion. Capsaicin pretreatment (in combination with hexamethonium) significantly inhibited golet cell discharge (by 80%) but had no significant effect on bronchoconstriction. We conclude that conjugated trimellitic anhydride challenge of trimellitic anhydride-sensitised guinea pigs induces goblet cell discharge and bronchoconstriction via different mechanisms with activation of capsaicin-sensitive sensory nerves responsible for secretion and histamine release responsible for airway constriction. The guinea pig model of trimellitic anhydride-induced occupational asthma may prove useful in examination of mechanisms of goblet cell secretion in allergic diseases.     

1,8‐Cineole induces relaxation in rat and guinea‐pig airway smooth muscle

Objectives 1,8‐Cineole is a monoterpene with anti‐inflammatory, vascular and intestinal smooth muscle relaxant activity. We have evaluated the potential bronchodilatatory activity of this compound. Methods 1,8‐Cineole was tested against carbachol, histamine, K⁺ 80 mM and ovalbumin‐induced bronchial contractions in Wistar rat or guinea‐pig tissues. Some of the guinea‐pigs had been previously sensitized with an intramuscular injection of 5% (w/v) ovalbumin/saline solution. Control animals received 0.3 ml saline. In separate experimental groups the response to 1,8‐cineole (1–30 mg/kg), phenoterol (0.05–5 mg/kg) or vehicle (0.3% Tween in saline) was studied. Key findings 1,8‐Cineole decreased, in vivo, rat bronchial resistance with similar efficacy as phenoterol (66.7 ± 3.2% vs 72.1 ± 5.3%). On the other hand, the maximal relaxant response to 1,8‐cineole in carbachol‐precontracted rat tracheas was 85.5 ± 5.7% (IC50 = 408.9 (328–5196) μg/ml) compared with 80.2 ± 4.8% (IC50 = 5.1 (4.3–6.1) μg/ml) with phenoterol. The addition of 1,8‐cineole to guinea‐pig tracheal rings tonically contracted with K⁺ 80 mM induced a concentration‐related relaxation. The maximal relaxation elicited by 1,8‐cineole was 113.6 ± 11.7% (IC50 127.0 (115.9–139.2) μg/ml) compared with 129.7 ± 14.6% (IC50 0.13 (0.12–0.14) μg/ml) achieved after phenoterol administration. In addition, the incubation of tracheal rings with 1,8‐cineole (100, 300 or 1000 μg/ml), 15 min before inducing phasic contractions with K⁺ 80 mM, decreased the maximal amplitude of the contraction by 31.6 ± 4.6, 75.7 ± 2.7 and 92.2 ± 1.5%, respectively. In another set of experiments, neither the maximal response nor the IC50 for the 1,8‐cineole‐induced relaxation were different between normal and ovalbumin‐sensitized tissues. Moreover, the relaxation of bronchial rings contracted after exposure to 1 μg/ml ovalbumin occurred at a faster rate in rings pre‐incubated with 1,8‐cineole when compared with rings pre‐incubated with vehicle only (Tween 0.3%). Therefore, in the first minute after the antigen challenge, the tracheal tissue relaxed after the peak contraction by 6.5, 21.4 (P < 0.05 vs control) and 66.9% (P < 0.05 vs control) in the presence of 100, 300 or 1000 μg/ml 1,8‐cineole, respectively. Conclusions 1,8‐Cineole relaxed rat and guinea‐pig (nonsensitized and ovalbumin‐sensitized) airway smooth muscle by a nonspecific mechanism.     

Acute hypersensitivity to aerosolized histamine induced by aerosolized ovalbumin in guinea pigs.

Acute airway hyperresponsiveness can be induced after exposure to aerosolized ovalbumin in sensitized guinea pigs. The purpose of the present studies was to determine if "pro-inflammatory agents" would potentiate and prolong antigen-induced pulmonary hyperresponsiveness to histamine in guinea pigs. Guinea pigs were sensitized to aerosolized ovalbumin by exposing them to a 3 min aerosol, generated ultrasonically from a 10% ovalbumin solution on day 0 and day 7. On day 13 the guinea pigs were exposed to a 3 min aerosol of deionized water or a pro-inflammatory agent (1 microgram/ml PAF, 1 mg/ml LPS, or 4% B. pertussis vaccine). Twenty-four hours later, on day 14, the conscious guinea pigs were challenged with a 3 min aerosolized ovalbumin exposure (under isoproterenol cover) and the individual guinea pig responsiveness to aerosolized histamine was determined 2 and 24 h later in an anesthetized modified Konzett-Rossler preparation. Under these experimental conditions, ovalbumin challenge to sensitized guinea pigs produced only an acute hyperresponsiveness (about a 3-10-fold shift) to aerosolized histamine, which lasted less than 24 h. The pro-inflammatory agents neither potentiated nor prolonged the duration of the hyperresponsiveness.     

The effect of stercuronium on cardiac muscarinic receptors

In the electrically stimulated guinea-pig left atrium preparation stercuronium (10^?6?3 × 10^?4 M) a short-acting neuromuscular blocking drug, was found to produce parallel displacement of concentration-response curves for negative inotropic responses to acetylcholine, carbachol, methacholine and pilocarpine but not those to ATP or K⁺. The effect of stercuronium was not modified in the presence of mecamylamine (2 × 10^?5 M) or propranolol (3 × 10^?6 M). It was concluded that stercuronium possesess antimuscarinic activity but in contrast to the competitive antagonist homatropine (2 × 10^?6?3 × 10^?4 M) the degree of antagonism of cholinomimetics tended towards a limiting value at high concentrations of antagonist being more marked with acetylcholine than with carbachol and the other cholinomimetics. Pretreatment of guinea pigs with dyflos (1.2 mg/kg s.c. daily for 3 days) reduced but did not abolish the difference between acetylcholine and carbachol. Using acetylcholine as the agonist in atria obtained from dyflos-pretreated guinea pigs combination of stercuronium and homatropine produced dose ratios which were significantly less than expected for combination of 2 competitive antagonists. It is suggested that the antimuscarinic activity of stercuronium is due to a non-competitive antagonism of the metaffinoid type whereby interaction at an allosteric site may modify the bining of agonists and of competitive antagonists for the receptor.     

Evaluation of the effect of Myrica sapida on bronchoconstriction and bronchial hyperreactivity

The present investigation was undertaken to evaluate the bronchodilator and bronchial hyperreactivity of the stem bark of Myrica sapida. Experimental models studied were histamine induced bronchospasm in guinea pigs, bronchoalveolar lavage fluid (BALF) in egg albumin sensitized guinea pigs, histamine release from the lung tissues of sensitized guinea pigs and histopathological studies. Ethanolic extract of M. sapida (75 mg/kg, p.o., for 7 days) showed significant protection against histamine aerosol induced bronchospasm. Significant decrease in the total and differential leukocyte counts in BALF and prevention of egg albumin induced histamine release from chopped lung tissues of sensitized guinea pigs was observed on chronic administration of ethanolic extract of M. sapida (75 mg/kg, p.o., for 15 days). Histological examination of the section of lung from sensitized guinea pigs treated with ethanolic extract of M. sapida (75 mg/kg, p.o., for 15 days) was comparable to that of the control group. These results suggest that M. sapida possesses not only bronchodilator activity but also decreases bronchial hyperresponsiveness by decreasing the infiltration of inflammatory mediators like eosinophils, neutrophils in BALF and inhibiting histamine release from lungs of sensitized guinea pigs.     

The effects of an anti-CD18 antibody (R15.7) in antigen-induced airway hyperresponsiveness (AH) and cell influx in guinea pigs.

Aerosol ovalbumin challenge (OA) of sensitized guinea pigs induced airway hyperreactivity (AH) to i.v. acetylcholine (Ach) and serotonin (5-HT) 24 hr post OA. Bronchoalveolar lavage fluid 24 hrs after OA showed increased leukocytes compared to unsensitized unchallenged animals. Treatment with monoclonal antibody R15.7 (3 mg/kg i.v.,) 1 hr prior and 4 hours after OA prevented the induction of AH to Ach but not to 5-HT and reduced influx of leukocytes. We conclude: 1) antigen inhalation induces an increase in AH with an increase in proinflammatory cell influx and 2) treatment with anti-CD18 antibody inhibits cell influx and airway hyperreactivity.     

Validation of a non-invasive technique to assess development of airway hyperreactivity in an animal model of immunologic pulmonary hypersensitivity

Airway hyperreactivity (AHR) is considered to be a prominent and consistent feature of the asthmatic. Accordingly, in developing animal models of asthma, it is important to have methodologies available for repeated assessment of airway reactivity (AR). We have described a methodology to assess AR in conscious minimally restrained guinea pigs, AR being quantified as the airborne concentration of histamine (mg m-3) necessary to produce a mild airway constriction. The present study sought to validate that methodology by assessing its ability to detect changes in AR associated with immediate-onset pulmonary hypersensitivity responses. Guinea pigs were sensitized by intraperitoneal injection of ovalbumin (OA) and challenged with OA aerosol 3 weeks later. All animals developed severe immediate-onset airway constrictive responses. AR was assessed 1 h later, upon return to normal breathing patterns. Hyperreactivity was apparent from response to 0.50 mg m-3 histamine when compared with 2.10 mg m-3 histamine needed for baseline response. In control, sham sensitized animals AR remained at 2.12 mg m-3 after OA inhalation challenge. The results demonstrate the ability of this methodology to detect airway hyperreactivity to histamine resulting from a pulmonary hypersensitivity response. By requiring neither surgery nor any invasive procedure, the technique is appropriate for serial measurements of AR as is needed in development of an animal model for asthma, a chronic airway disease.