Airway Hyperresponsiveness in Anaesthetised Guinea-Pigs 18–24 Hours after Antigen Inhalation Does Not Occur with All Intravenously Administered Spasmogens

Abstract: Actively sensitised guinea-pigs were exposed to inhalation challenges with ovalbumin aerosol (macro- and microshock) and airway responsiveness to six intravenously administered spasmogens was evaluated 18 to 24 hr later in the anaesthetised animal. An increase in airway sensitivity was defined as a significant leftward shift of the dose-response curve when compared with saline-challenged control sensitized animals. After ovalbumin-macroshock (1% ovalbumin for 2 min. with mepyramine cover against fatal anaphylaxis), airway hyperresponsiveness was seen to 5-HT, the thromboxane A₂-mimetic, U-46619, and bradykinin but not to methacholine, histamine or substance P. A similar pattern was seen after ovalbumin-microshock (0.01% ovalbumin for 60 min.), with induction of airway hyperreactivity to 5-HT and U-46619 but not methacholine or histamine. When the U-46619 dose-response curve was constructed following treatment of the animals with atropine (1 mg/kg, intravenously), airway hyperresponsiveness was no longer significant. As an index of airway inflammation, lung weights were significantly heavier in ovalbumin-challenged animals, than in saline-challenged controls. The results of this study with intravenously administered spasmogens does not support claims that ovalbumin-induced airway hyperreactivity in the guinea-pig is a ‘non-specific’phenomenon.     

Airway hyperreactivity follows anaphylactic microshock in anaesthetized guinea-pigs

Actively sensitized guinea-pigs were challenged with a dose of ovalbumin aerosol (300 micrograms ml-1, 5 s) that caused submaximal bronchoconstriction (anaphylactic microshock). Airway reactivity to i.v. 5-hydroxytryptamine (5-HT), i.v. acetylcholine (ACh) and aerosolised 5-HT was assessed subsequently. In addition, histological studies were carried out to investigate possible pulmonary recruitment of inflammatory cells following anaphylactic microshock. Following antigen challenge, there was a significant (P less than 0.05) increase in airway reactivity. This phenomenon was temporally separated (60-120 min) from the initial anaphylactic bronchoconstriction, but occurred in the absence of detectable lung pathology other than minor epithelial necrosis. Whilst histamine aerosol (100 micrograms ml-1, 5 s) did not induce airway hyperreactivity, pretreatment with the histamine H1 receptor antagonist mepyramine (2 mg kg-1 i.v.) prevented that occurring following antigen challenge. These observations suggest that in the pathogenesis of airway hyperreactivity, mediator release from resident leukocytes is initially more important than pulmonary infiltration of circulating cells. Depletion of a putative epithelium-derived relaxant factor may also play a contributory role. The anaphylactic release of histamine may modulate the release of secondary mediators of airway hyperreactivity.     

Airway hyperresponsiveness in anaesthetised guinea-pigs 18-24 hours after antigen inhalation does not occur with all intravenously administered spasmogens.

Actively sensitised guinea-pigs were exposed to inhalation challenges with ovalbumin aerosol (macro- and microshock) and airway responsiveness to six intravenously administered spasmogens was evaluated 18 to 24 hr later in the anaesthetised animal. An increase in airway sensitivity was defined as a significant leftward shift of the dose-response curve when compared with saline-challenged control sensitized animals. After ovalbumin-macroshock (1% ovalbumin for 2 min. with mepyramine cover against fatal anaphylaxis), airway hyperresponsiveness was seen to 5-HT, the thromboxane A2-mimetic, U-46619, and bradykinin but not to methacholine, histamine or substance P. A similar pattern was seen after ovalbumin-microshock (0.010% ovalbumin for 60 min.), with induction of airway hyperreactivity to 5-HT and U-46619 but not methacholine or histamine. When the U-46619 dose-response curve was constructed following treatment of the animals with atropine (1 mg/kg, intravenously), airway hyperresponsiveness was no longer significant. As an index of airway inflammation, lung weights were significantly heavier in ovalbumin-challenged animals, than in saline-challenged controls. The results of this study with intravenously administered spasmogens does not support claims that ovalbumin-induced airway hyperreactivity in the guinea-pig is a 'non-specific' phenomenon.     

Airway hyperreactivity induced by active cigarette smoke exposure in guinea-pigs: possible role of sensory neuropeptides

Exposure to cigarette smoke is associated with increased airway responsiveness to different stimuli, both in human and animal studies. However, the mechanisms involved in the pathogenesis of smoke-induced airway hyperreactivity are less clear. We investigated the development of airway hyperreactivity induced by active cigarette smoke exposure in anaesthetised guinea-pigs and the possible mechanisms involved. Active inhalation of cigarette smoke (15 s/min for 10 min) potentiated the bronchocontractile effect of acetylcholine (Ach), indicating the occurrence of airway hyperreactivity. This phenomenon appeared within 5 min and lasted up to 50 min after smoke exposure. Smoke induced airway hyperreactivity was a non-specific phenomenon, involving an enhanced responsiveness to both Ach and histamine (Hist). Recruitment of proinflammatory cells into the airway lumen, as revealed by the analysis of bronchoalveolar lavage fluid, paralleled the development of the hyperreactive phenomenon, suggesting a relationship between the inflammatory reaction and the genesis of smoke-induced airway hyperreactivity. Cervical bilateral vagotomy did not modify either the degree and the time-course of smoke induced airway hyperreactivity. Moreover, atropine treatment did not affect the increase in Hist response due to smoke inhalation. On the other hand, depletion of substance P due to capsaicin pretreatment almost completely prevented the capacity of cigarette smoke to potentiate Ach induced bronchoconstriction. Cyclo-oxygenase inhibition, by indomethacin pretreatment, reduced the time course of the hyperreactivity induced by smoke inhalation. Our results clearly demonstrate the occurrence of airway hyperreactivity triggered by active cigarette smoke exposure. Moreover, the data obtained suggest a predominant role for substance P and related peptides in the pathogenesis of smoke induced increase in airway responsiveness.     

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.     

Role of nitric oxide in the development and partial reversal of allergen-induced airway hyperreactivity in conscious,unrestrained guinea-pigs

1. Using a conscious, unrestrained guinea-pig model of allergic asthma, we investigated the role of endogenous nitric oxide (NO) in the regulation of airway (hyper)reactivity to histamine before and after the allergen-induced early and late asthmatic reactions, by examining the effect of inhalation of the NO synthase inhibitor N^ω-nitro-L-arginine methyl ester (L-NAME, 12 mM, 15 min) on the histamine-induced airway obstruction of ovalbumin-sensitized guinea-pigs before, and at 5.5 h and 23.5 h after allergen challenge.
2. Before allergen challenge, inhaled L-NAME caused a significant 2.02±0.25 fold increase (P<0.01) in airway reactivity to histamine; this effect was reversed within 2.5 to 6 h after administration.
3. After the allergen-induced early asthmatic reaction at 5 h after ovalbumin provocation, a significant 3.73±0.67 fold increase (P<0.01) of the airway reactivity to histamine was observed; subsequent inhalation of L-NAME at 5.5 h had no effect on the airway hyperreactivity, reassessed at 6 h.
4. After the late asthmatic reaction, at 23 h after ovalbumin provocation, a reduced, but still significant airway hyperreactivity to histamine (2.18±0.40 fold; P<0.05) was observed. Subsequent inhalation of L-NAME now significantly potentiated the partially reduced airway hyperreactivity 1.57±0.19 fold (P<0.05) to the level observed after the early asthmatic reaction.
5. When administered 30 min before allergen exposure, L-NAME significantly enhanced the allergen-induced early asthmatic reaction. However, when administered at 5.5 h after allergen provocation, L-NAME did not affect the subsequent late asthmatic reaction.
6. These results indicate that endogenous NO is involved the regulation of histamine- and allergen-induced bronchoconstriction and that a deficiency of cNOS-derived NO contributes to the allergen-induced airway hyperreactivity to histamine after the early asthmatic reaction, while a recovery of NO deficiency may account for the partial reversal of the allergen-induced airway hyperreactivity after the late asthmatic reaction.

     

Nedocromil sodium prevents airway hyperreactivity induced by cigarette smoke in anaesthetized guinea-pigs

Increased airway reactivity and influx of inflammatory cells into the airways have been demonstrated both in smokers and after smoke exposure in animal studies. We investigated the ability of nedocromil sodium and hydrocortisone to protect from the pathological alterations induced by direct cigarette smoke exposure in anaesthetized guinea-pigs. Active inhalation of cigarette smoke (15 s/min for 10 min) induced airway hyperreactivity, as shown by the enhanced bronchoconstrictor effect of histamine and was associated with an increase in total cells, macrophages and eosinophils in the BAL fluid. Nedocromil sodium given by aerosol (3 and 10 mg/ml for 30 s) completely prevented the ability of cigarette smoke to potentiate histamine induced bronchoconstriction. In parallel, nedocromil sodium inhibited the development of the inflammatory reaction triggered by smoke exposure. Hydrocortisone pretreatment (50 mg/kg s.c. twice) did not abolish the smoke induced airway hyperreactivity, nor did it inhibit the recruitment of proinflammatory cells within the airway lumen. Sensory neuropeptides have been demonstrated to be involved in the development of smoke induced airway hyperreactivity. The efficacy of nedocromil sodium in this model might depend on its ability to modulate the activation of the peptidergic system.     

RP 58802B,a long-acting β2-adrenoceptor agonist: Assessment of antiasthma activity in the guinea-pig in vivo

We have examined the protective actions of RP 58802B, a novel β₂-adrenoceptor agonist, administered by the inhaled and oral routes in the anaesthetized and conscious guinea-pig against bronchospasm induced by histamine or antigen (ovalbumin). We have also examined the effects of RP 58802B on airway reactivity and inflammatory cell infiltration in platelet-activating factor (PAF) (aerosol)-induced bronchial hyperreactivity and on PAF (tracheal instillation)-induced microvascular leakage in the guinea-pig. Nebulized RP 58802B produced a rapid onset and long lasting inhibition of histamine-induced bronchospasm in the anaesthetized guinea-pig (EC₅₀ = 3.2 ± 0.9 μg/ml; duration >90 min). Given orally, RP 58802B (5 mg/kg, 60 min before challenge) produced a >three-fold shift to the right of the dose-response curve and depressed the maximum response to histamine by 39 ± 11%. Increasing the concentration to 25 mg/kg had no further effect. Similar protection was still seen 4 h after oral dosing. In conscious guinea-pigs, RP 58802B (5 or 25 mg/kg, p.o. 60 min before challenge) significantly attenuated antigen-induced dyspnoea with the time to severe dyspnoea increasing from 170 ± 32 to 325 ± 32 s at the higher dose of drug. RP 58802B (10 or 25 mg/kg, p.o. 60 min before exposure to PAF) prevented the development of bronchial hyperreactivity. Although PAF-induced bronchial hyperreactivity was not accompanied by an increase in the number of pulmonary eosinophils, RP 58802B (25 mg/kg p.o.) reduced the numbers of eosinophils recovered by lavage. RP 58802B (10 mg/kg p.o.) significantly inhibited PAF-induced microvascular leakage into guinea-pig lung. These data suggest that RP 58802B, in addition to being a potent and long acting bronchodilator, may have a prophylactic role in preventing bronchial hyperreactivity and in reducing plasma exudation into the lungs.     

Airway reactivity, inflammatory cell influx and nitric oxide in guinea-pig airways after lipopolysaccharide inhalation

1. The aim of this study was to investigate the relationship between airway reactivity, leukocyte influx and nitric oxide (NO), in conscious guinea-pigs after aerosolized lipopolysaccharide (LPS) exposure. 2. Inhaled histamine (1 mM, 20 s), causing no bronchoconstriction before LPS exposure (30 microg ml(-1), 1 h), caused bronchoconstriction at 0.5 and 1 h (P:<0.02) after LPS exposure. This airway hyperreactivity (AHR) recovered by 2 h. In contrast, 48 h after LPS exposure, the response from a previously bronchoconstrictor dose of histamine (3 mM, 20 s) was attenuated (P:<0.01) i.e. airway hyporeactivity (AHOR). 3. Investigation of the cellular content of bronchoalveolar lavage fluid (BALF) from these animals revealed a rapid (0.5 h: 691 fold increase) and progressive neutrophil influx after LPS exposure (24 h: 36.3+/-2.3x10(6) cells per sample), that subsided 48 h later. Macrophages and eosinophils also time-dependently increased (0.5 h: 4.6+/-0.4 and 0.1+/-0.05; 48 h: 31.0+/-6.0 and 1.8+/-0.3x10(6) cells per sample, respectively) after LPS, compared to vehicle exposure (24 h: neutrophils, eosinophils and macrophages: 0.28+/-0.19, 0.31+/-0.04 and 4.96+/-0. 43x10(6) cells per sample, respectively). 4. The combined NO metabolites in BALF, after vehicle (1 h), or LPS (1 h: AHR and 48 h: AHOR) exposure, were respectively increased (41%, P:<0.01), decreased (47%, P:<0.01) and further increased (80%, P:<0.001), compared with na?ve animals. 5. Inhaled N(o)-nitro-L-arginine methyl ester (L-NAME: 1.2 and 12 mM, 15 min), reduced BALF NO metabolites 2 h later, but did not cause AHR to histamine (P:>0.05). When L-NAME inhalation followed LPS, AHR was prolonged from 1 h to at least 4 h (P:<0.01). 6. In summary, aerosolized LPS inhalation caused neutrophil and macrophage airways infiltration, and an early development of AHR followed 48 h later by AHOR to histamine. AHR and AHOR coincided with a respective reduction and elevation in airways NO (metabolites). Thus, NO may aid recovery from AHR, as inhibition of its production prolongs AHR. However, NO deficiency alone is not responsible for LPS-induced AHR.     

Induction of transient airway hyperresponsiveness by exposure to 4 ppm nitrogen dioxide in guinea pigs.

In the present study, we investigated (1) whether airway responsiveness to inhaled histamine-aerosol could be induced during 7-d exposure of guinea pigs to 4 ppm NO2 and, if so, (2) whether thromboxane A2 may be involved in such increase. Female Hartley guinea pigs were divided into 6 groups (n = 15/group). Three groups were exposed to filtered air and the other 3 groups were exposed to NO2 for 1, 3, or 7 d (24 h/d). Baseline specific airway resistance (SRaw0) did not change significantly after exposure to 4 ppm NO2 or air. Airway responsiveness was determined 1 wk before the beginning of exposure and on the day of termination of the exposure. Prior to exposure to NO2, the EC200His, the concentrations of inhaled histamine necessary to double SRawNaCl (SRaw after inhalation of 0.9% NaCl), were 1.07 +/- 0.20, 1.30 +/- 0.20, and 1.01 +/- 0.18 mM for the 3 groups later given NO2 for 1, 3, and 7 d, respectively. Following exposure to NO2 for 1, 3, or 7 d, EC200His values were 1.42 +/- 0.25, 0.66 +/- 0.10 (p < .05), and 1.05 +/- 0.22 mM, respectively. These results show that 7-d exposure to 4 ppm NO2 induced a significant increase in airway responsiveness on d 3. Exposure to air had no significant effect on the airway responsiveness. This transient hyperresponsiveness was inhibited by a specific inhibitor of thromboxane synthetase, OKY 046. These results indicated that (1) a lower concentration (4 ppm) of NO2 than that previously reported can induce transient hyperresponsiveness in guinea pigs during appropriate long-term exposure, and (2) thromboxane A2 may play an important role in this transient airway hyperresponsiveness.     

Colchicine Decreases Airway Hyperreactivity Afrer Phosgene Exposure

Abstract

Phosgene (COCl₂) exposure affects an influx of inflammatory cells into the lung, which can be reduced in an animal model by pretreatment with colchicine. Inflammation in the respiratory tract can be associated with an increase in airway hyperreactivity. We tested the hypotheses that (1) phosgene exposure increases airway reactivity and (2) colchicine can decrease this elevation. Sprague Dawley rats (70 d old; male) were exposed to 1 ppm COCl₂ for 1 h. Airway reactivity was tested at 0, 4, and 24 h postexposure by infusing anesthetized animals intravenously with acetylcholine and assessing expiratory resistance and dynamic compliance. Immediately and 4 h postexposure, a significant change in expiratory resistance and dynamic compliance was observed in those animals exposed to COCl₂, while at 24 h this response was greater. A second experiment was performed in rats pretreated with colchicine (1 mg/kg) or saline given intraperitoneally, exposed to 1 ppm COCl₂ for 1 h, with both expiratory resistance and dynamic compliance assessed at 24 h. After exposure, cell differentials and protein in lavage were also quantitated. The results indicate that colchicine decreased neutrophil influx, protein accumulation, and changes in both expiratory resistance and dynamic compliance after COCl₂ exposure. Colchicine may affect injury and changes in expiratory resistance and dynamic compliance by diminishing the incursion of inflammatory cells, but other properties of this medication may also be responsible for the observed results.     

Prevention of non-specific airway hyperreactivity after allergen challenge in guinea-pigs by the PAF receptor antagonist SDZ 64-412.

1. Allergen challenge by aerosol in sensitized guinea-pigs elicited non-specific airway hyperreactivity assessed by reactivity to i.v. histamine or acetylcholine. Airway hyperreactivity to histamine persisted for at least 48 h and was accompanied by pulmonary eosinophilia as determined by bronchoalveolar lavage cell analysis. 2. Airway hyperreactivity was independent of vagal reflex mechanisms since it was not abrogated by bilateral vagotomy. 3. The novel platelet-activating factor (PAF) receptor antagonist SDZ 64-412 inhibited the development of airway hyperreactivity, as measured 24 h after aerosol allergen challenge, when given as a single treatment orally 2 h before allergen challenge. The PAF receptor antagonist WEB 2086 as well as methylprednisolone and ketotifen also showed efficacy in preventing development of airway hyperreactivity. 4. Neither the two PAF antagonists nor ketotifen had any effect on bronchoalveolar lavage (BAL) eosinophil numbers. Methylprednisolone was the only substance which readily prevented eosinophil recruitment in addition to airway hyperreactivity. 5. We conclude that allergen-induced airway hyperreactivity in guinea-pigs is inhibited by prophylactic anti-asthma drugs and specific PAF receptor antagonists, thus demonstrating a pivotal role of PAF in this response. There was a lack of correlation between airway hyperreactivity and the presence of BAL eosinophils.     

Continued inhalation of lidocaine suppresses antigen-induced airway hyperreactivity and airway inflammation in ovalbumin-sensitized guinea pigs

It is unclear whether inhaled lidocaine is effective against airway hyperreactivity and inflammation in asthma. The aim of this study was to investigate the effects of inhaled lidocaine on airway hyperreactivity and inflammation. Airway reactivity to inhaled histamine, cellular composition of bronchoalveolar lavage (BAL) fluid, plasma substance P (SP), and isolated lung tissue were evaluated in ovalbumin (OVA)-sensitized guinea pigs 7 days after OVA challenge. The effects of inhaled lidocaine on this model were also evaluated. Treatment with lidocaine was administered in two fashions: as single inhalation or inhalation bid for 7 consecutive days, for comparison with a saline-inhaled control group. Airway hyperreactivity to histamine, increase in number of total cells and increased proportion of eosinophils in BAL fluid, and marked eosinophil infiltration in airway walls were noted even 7 days after OVA challenge in the control group. Plasma SP level was also significantly increased. Although treatment with single lidocaine inhalation did not affect airway hyperreactivity, continued inhalation (bid for 7 days) attenuated airway hyperreactivity. Continued, but not single, inhalation of lidocaine also suppressed infiltration of eosinophils in BAL fluid and in airway walls. In addition, plasma SP levels were significantly reduced by continued but not by single inhalation. It appears possible that lidocaine when inhaled suppresses eosinophilic inflammation of the airway and SP-induced neurogenic inflammation, leading to alleviation of airway hyperreactivity.     

Ovalbumin-Induced Airway Inflammation and Fibrosis in Mice Also Exposed to Ultrafine Particles

A murine model of allergen-induced airway inflammation was used to examine the effects of exposure to ultrafine particles (PM_2.5) on airway inflammation and remodeling. Lung inflammation was measured by quantitative differential evaluation of lung lavage cells. Alterations in lung structure (airway remodeling and fibrosis) were evaluated by quantitative biochemical analysis of microdissected airways and by histological evaluation of stained lung sections. The same total number of cells was observed in lavage fluid from animals exposed for 4 wk to ovalbumin alone or to ovalbumin for 4 wk immediately before or after 6 exposures over a period of 2 wk to 235 ug/m³ of PM_2.5. Mice exposed to ovalbumin for 6 wk with concurrent exposure to PM_2.5 during wk 5–6 had a significant decrease in the total number of cells recovered by lavage as compared with the group exposed to ovalbumin alone. There were no significant differences in the cell differential counts in the lavage fluid from mice exposed to ovalbumin alone as compared with values from mice exposed to ovalbumin and PM_2.5 under the protocols studied. Airway structural changes (remodeling) were examined by three different quantitative methods. None of the groups exposed to ovalbumin and PM had a significant increase in airway collagen content evaluated biochemically (i.e., total airway collagen) as compared to the matched groups of mice exposed to ovalbumin alone. Airway collagen content evaluated histologically by sirius red staining showed significant increases in all of the animals exposed to ovalbumin, with or without PM, and no apparent difference between the ovalbumin group and mice exposed to PM with ovalbumin. The findings were consistent with an additive, or less than additive, response of mice to exposure to PM and ovalbumin. Air or PM exposure alone for 2 wk did not result in observable goblet cells in the airways, while mice exposed to ovalbumin aerosol alone for 4 wk had about 20–25% goblet cells in their conducting airways. Sequential exposure to ovalbumin and PM (or vice versa) caused significant increases in goblet cells (to about 35% of total cells) in the conducting airways of the exposed mice. We conclude that when mice with allergen-induced airway inflammation induced by ovalbumin are also exposed to PM_2.5, the lung inflammatory response and airway remodeling may be modified, but that this altered response is dependent upon the sequence of exposure and the duration of exposure to ovalbumin aerosol. At the concentrations of PM tested, we did not see changes in airway fibrosis or airway reactivity for animals exposed to ovalbumin and PM_2.5 as compared with animals exposed only to ovalbumin aerosol. However, goblet-cell hyperplasia was significantly increased in mice exposed concurrently to ovalbumin and PM_2.5 as compared with mice exposed to ovalbumin alone.     

Effects of Gasoline Engine Emissions on Preexisting Allergic Airway Responses in Mice

Gasoline-powered vehicle emissions contribute significantly to ambient air pollution. We hypothesized that exposure to gasoline engine emissions (GEE) may exacerbate preexisting allergic airway responses. Male BALB/c mice were sensitized by injection with ovalbumin (OVA) and then received a 10-min aerosolized OVA challenge. Parallel groups were sham-sensitized with saline. Mice were exposed 6 h/day to air (control, C) or GEE containing particulate matter (PM) at low (L), medium (M), or high (H) concentrations, or to the H level with PM removed by filtration (high-filtered, HF). Immediately after GEE exposure mice received another 10-min aerosol OVA challenge (pre-OVA protocol). In a second (post-OVA) protocol, mice were similarly sensitized but only challenged to OVA before air or GEE exposure. Measurements of airway hyperresponsiveness (AHR), bronchoalveolar lavage (BAL), and blood collection were performed ～24 h after the last exposure. In both protocols, M, H, and HF GEE exposure significantly decreased BAL neutrophils from nonsensitized mice but had no significant effect on BAL cells from OVA-sensitized mice. In the pre-OVA protocol, GEE exposure increased OVA-specific IgG₁ but had no effect on BAL interleukin (IL)-2, IL-4, IL-13, or interferon (IFN)-γ in OVA-sensitized mice. Nonsensitized GEE-exposed mice had increased OVA-specific IgG_2a, IgE, and IL-2, but decreased total IgE. In the post-OVA protocol, GEE exposure reduced BAL IL-4, IL-5, and IFN-γ in nonsensitized mice but had no effect on sensitized mice. These results suggest acute exposure to the gas–vapor phase of GEE suppressed inflammatory cells and cytokines from nonsensitized mice but did not substantially exacerbate allergic responses.     

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.     

Airway function,oedema, cell infiltration and nitric oxide generation in conscious ozone-exposed guinea-pigs: effects of dexamethasone and rolipram

1. The effects of ozone inhalation (90 min, 2.15+/-0.05 p.p.m.) and their modification by dexamethasone (20 mg kg(-1)) or the phosphodiesterase-4 inhibitor, rolipram (1 mg kg(-1)), administered (i.p.) 24 and 0.5 h before and 24 h after ozone exposure were examined in conscious guinea-pigs. 2. Ozone caused an early-phase bronchoconstriction (EPB) as a fall in specific airways conductance (sG(aw)) measured by whole body plethysmography, followed at 5 h by a late-phase bronchoconstriction (LPB) and increased respiratory rate. Rolipram did not alter this profile but dexamethasone inhibited the EPB. 3. Airway hyperreactivity to inhaled histamine (1 mM, 20 s) occurred at 0.5, 2, 12, 24 and 48 h after ozone inhalation, the 2 h change being abolished by rolipram and dexamethasone. 4. Bronchoalveolar lavage fluid (BALF) macrophages, eosinophils and neutrophils were significantly (P<0.05) elevated at 12, 24 and 48 h after ozone exposure, the 48 h influx being significantly attenuated (P<0.05) by rolipram and dexamethasone. 5. BALF nitric oxide (NO) metabolites decreased 0.5 h after ozone exposure by 52%, recovered at 2 h and significantly increased at 12 (101%) and 24 h (127%). The elevated NO was unaffected by rolipram or dexamethasone. 6. Lung oedema, measured from wet/dry weight differences, was significant 12, 24 and 48 h after ozone exposure, the latter being significantly attenuated (P<0.05) by rolipram and dexamethasone. 7. Ozone exposure of guinea-pigs produced features common to COPD. Although rolipram and dexamethasone did not affect the airway function changes, they inhibited the inflammation, airway hyperreactivity and oedema.     

Effects of selective phosphodiesterase inhibitors on platelet-activating factor- and antigen-induced airway hyperreactivity, eosinophil accumulation, and microvascular leakage in guinea pigs

There is currently interest in the potential use of selective inhibitors of cyclic nucleotide phosphodiesterases (PDE) in the treatment of asthma. In this study we examined the effects of three selective PDE inhibitors, milrinone (PDE III), rolipram (PDE IV) and zaprinast (PDE V), on the broncoconstriction produced by antigen and histamine, the airway hyperreactivity and microvascular leakage after aerosol exposure to platelet-activating factor (PAF) and antigen, and the antigen-induced eosinophil infiltration in guinea-pig lung. Inhaled rolipram (0.01–10 mg ml^–1) inhibited dose dependently the bronchospasm produced by aerosol antigen (5 mg ml^–1) an anaesthetised, ventilated guinea-pigs. Rolipram (10 mg ml^–1) produced maximal inhibition of antigen-induced bronchoconstriction but only partial inhibition of the response to aerosol histamine (1 mg ml^–1). Milrinone and zaprinast (each 10 mg ml^–1) showed weak, or no, inhibitory effects against bronchoconstriction produced by aerosol antigen or histamine. Pretreatment with rolipram (10 mg kg^–1, i.p.) prevented airway hyperreactivity to histamine which develops 24 h after exposure of conscious guinea-pigs to aerosol PAF (500 g ml^–1) or antigen (5 mg ml^–1). The pulmonary eosinophil infiltration obtained with 24 h of antigen-exposure was inhibited by rolipram. In contrast, milrinone and zaprinast (each 10 mg kg^–1, i.p.) failed to reduce either the airway hyperreactivity of the eosinophil accumulation in these animals. Rolipram (1–10 mg ml^–1) reduced the extravasation of Evans blue after aerosol PAF (500 g ml^–1) at all airway levels while a lower dose (0.1 mg ml^–1) was only effective at intrapulmonary airways. Rolipram (0.01–1 mg ml^–1) markedly reduced airway extravasation produced by inhaled antigen (5 mg ml^–1). Zaprinast (1–10 mg ml^–1) was also effective against airway microvascular leakage produced by aerosol PAF or antigen while milrinone (10 mg ml^–1) had no antiexudative effect. These data support previous suggestions that pharmacological inhibition of PDE IV results in anti-spasmogenic and anti-inflammatory effects in the airways and may be useful in the treatment of asthma.     

Dichloromethane inhalation, carboxyhemoglobin concentrations, and drug metabolizing enzymes in rabbits.

The relationship between inhaled dichloromethane (DCM) and percentage of carboxyhemoglobin (% COHb) in blood has been investigated in rabbits. After a single 20-min exposure to DCM, % COHb rose to a maximum within 2–3 hr and usually declined to basal values within 8 hr. The maximum COHb concentration and the time to reach that value were DCM concentration-dependent. In rabbits given a 4-hr exposure to DCM, % COHb increased over the first 2–3 hr, reaching a peak by about 4 hr with a return to basal levels within 24 hr. Studies were carried out to determine whether treatment with modifiers of hepatic mixed-function oxidase changed the % COHb response after DCM exposure. Of the compounds investigated, only CCl₄ and phenobarbital altered % COHb resulting from DCM inhalation. As expected, CCl₄, a potent hepatotoxin, reduced the % COHb resulting from DCM inhalation. Contrary to expectations phenobarbital also lowered the COHb response from DCM inhalation although the decrease was not as marked as that caused by CCl₄.     

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.