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.

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.

Effects of aerosolised substance P on lung resistance in guinea-pigs: a comparison between inhibition of neutral endopeptidase and angiotensin-converting enzyme.

1. We have examined in guinea-pigs, in vivo, the effects of inhibition of neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE) on the airway response to aerosolised substance P (SP). We aerosolised captopril (4.6 mM, 60 breaths; 210 nmol) to inhibit ACE and acetorphan (0.3, 1 and 3 mM, 60 breaths; 9 nmol, 33 nmol and 110 nmol respectively) to inhibit NEP. We also examined the effect of the highest dose of acetorphan (110 nmol) on the response to aerosolised acetylcholine (ACh). 2. Responsiveness to SP (or ACh) was measured as the change in lung resistance (RL) induced by nebulisation of increasing concentrations of SP (or ACh) before and after treatment with the inhibitor. PC200, defined as the provocative concentration inducing an increase in RL of 200% above baseline was calculated for each challenge. 3. Administration of acetorphan before the second SP-challenge induced a dose-dependent decrease in PC200 for SP amounting to 1.8 (+/- 0.3) log units after treatment with 11 nmol acetorphan. Treatment with vehicle before the second SP-challenge or with 3 mM acetorphan before the second ACh-challenge had no significant effect on PC200. 4. Treatment with captopril (21 nmol) induced only a small, nonsignificant leftward shift of PC200 to SP (0.3 +/- 0.2 log units). 5. We conclude that a NEP-like enzyme, but not ACE, regulates the response to aerosolised SP. We suggest that the same is true for SP released endogenously from sensory nerve endings in the airway epithelial layer.

Peptidase modulation of noncholinergic vagal bronchoconstriction and airway microvascular leakage.

We investigated whether inhibition of neutral endopeptidase 24.11 (NEP) and/or angiotensin-converting enzyme (ACE) modifies vagally induced nonadrenergic noncholinergic (NANC) airflow obstruction and airway microvascular leakage as measured by extravasation of Evans blue dye (intravenous) in anesthetized guinea pigs. We gave phosphoramidon to inhibit NEP and enalapril maleate or captopril to inhibit ACE. Animals pretreated with inhaled phosphoramidon (7.5 or 75 nmol), enalapril maleate (87 or 870 nmol), or captopril (350 nmol) reached higher peak lung resistance (RL) values (14.3 +/- 2.7, 15.7 +/- 3.8, 16.7 +/- 3.8, 11.4 +/- 1.6, and 24.6 +/- 3.5 cmH2O.ml-1.s, respectively) than saline-treated animals (5.9 +/- 1.1; P less than 0.05) after bilateral vagus nerve stimulation (5 Hz, 10 V, 10 ms, 150 s). Intravenous phosphoramidon (1 mg/kg), but not intravenous captopril (6 mg/kg), potentiated peak RL (22.9 +/- 6.9 and 7.1 +/- 1.5 cmH2O.ml-1.s, respectively). Vagal nerve stimulation (1 and 5 Hz) increased the extravasation of Evans blue dye in tracheobronchial tissues compared with sham-stimulated animals, but this was not potentiated by inhaled enzyme inhibitors or intravenous captopril. However, intravenous phosphoramidon significantly augmented the extravasation of Evans blue dye in main bronchi and intrapulmonary airways. We conclude that degradative enzymes regulate both NANC-induced airflow obstruction and airway microvascular leakage.

Role of thromboxane A2 in airway microvascular leakage induced by inhaled platelet-activating factor.

We studied the effects of OKY-046 (1, 10, and 30 mg/kg iv), a selective thromboxane synthase inhibitor, and of ICI 192605 (0.5 mg/kg), a selective thromboxane A2 receptor antagonist, on airflow obstruction and airway microvascular leakage induced by inhaled platelet-activating factor (PAF). Extravasated Evans blue dye content was measured as a reflection of airway microvascular leakage. In control animals, PAF caused a significantly higher increase in extravasation of dye and significantly less increase in lung resistance (RL) than histamine. OKY-046 significantly inhibited both changes in RL and airway microvascular leakage after PAF in a dose-dependent manner, whereas it inhibited histamine-induced airway microvascular leakage only at main bronchi, without any significant effect on RL. ICI 192605 significantly inhibited both RL and airway microvascular leakage induced by PAF, but not after histamine. After both PAF and histamine, changes in RL correlated significantly with the degree of microvascular leakage. Airway microvascular leakage and airflow obstruction after PAF, but not after histamine, may be dependent on thromboxane A2 generation.

Airflow obstruction after substance P aerosol: contribution of airway and pulmonary edema.

We have studied the effects of aerosolized substance P (SP) in guinea pigs with reference to lung resistance and dynamic compliance changes and their recovery after hyperinflation. In addition, we have examined the concomitant formation of airway microvascular leakage and lung edema. Increasing breaths of SP (1.5 mg/ml, 1.1 mM), methacholine (0.15 mg/ml, 0.76 mM), or 0.9% saline were administered to tracheostomized and mechanically ventilated guinea pigs. Lung resistance (RL) increased dose dependently with a maximum effect of 963 +/- 85% of baseline values (mean +/- SE) after SP (60 breaths) and 1,388 +/- 357% after methacholine (60 breaths). After repeated hyperinflations, methacholine-treated animals returned to baseline, but after SP, mean RL was still raised (292 +/- 37%; P less than 0.005). Airway microvascular leakage, measured by extravasation of Evans Blue dye, occurred in the brain bronchi and intrapulmonary airways after SP but not after methacholine. There was a significant correlation between RL after hyperinflation and Evans Blue dye extravasation in intrapulmonary airways (distal: r = 0.89, P less than 0.005; proximal: r = 0.85, P less than 0.01). Examination of frozen sections for peribronchial and perivascular cuffs of edema and for alveolar flooding showed significant degrees of pulmonary edema for animals treated with SP compared with those treated with methacholine or saline. We conclude that the inability of hyperinflation to fully reverse changes in RL after SP may be due to the formation of both airway and pulmonary edema, which may also contribute to the deterioration in RL.

Bradykinin-induced airway microvascular 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 (RL). Bradykinin was given by inhalation (0.1, 0.3 and 1 mM; 45 breaths), and caused a dose-dependent increase in both RL 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 RL induced by inhaled bradykinin. Recovery RL 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.

Inhaled formoterol inhibits histamine-induced airflow obstruction and airway microvascular leakage.

We studied the effects of inhaled formoterol (0.75 mg/ml, 60 breaths = 26 micrograms), a long-acting beta 2-adrenoceptor agonist, or of the more short-acting drug, salbutamol (25 mg/ml, 60 breaths = 875 micrograms), on acute airflow obstruction and airway microvascular leakage (MVL) induced by inhaled histamine in anesthetized guinea pigs. Lung resistance (RL) and its recovery following hyperinflation (recovery RL) were measured for 6 min after histamine (1 or 2 mg/ml, 30 breaths) in animals pretreated with either inhaled beta 2-adrenoceptor agonist or inhaled saline (0.9%, 60 breaths). MVL was measured by determining the amount of extravasated Evans blue dye at various airway levels. Histamine increased RL dose dependently with a mean peak RL (+/- S.E.M.) of 13.1 +/- 2.41 cmH2O/ml per s after 2 mg/ml of histamine. Both formoterol and salbutamol significantly inhibited both peak and recovery RL and MVL to a similar degree. There was a significant correlation between the degree of extravasated dye and both peak and recovery RL, suggesting that MVL partly contributes to histamine-induced airflow obstruction. Formoterol is approximately 35 times more potent than salbutamol to inhibit both MVL and airflow obstruction induced by histamine aerosol.

The effect of inhaled K+ channel openers on bronchoconstriction and airway microvascular leakage in anaesthetised guinea pigs.

Since orally administered K+ channel openers may have cardiovascular side effects, it is possible that inhaled administration would be preferred for the treatment of asthma. We have investigated whether inhaled levcromakalim and HOE 234 inhibit histamine-induced bronchoconstriction and airway plasma exudation in anaesthetised guinea pigs. We have also investigated whether inhaled HOE 234 inhibits the bronchoconstriction and plasma exudation induced by vagus nerve stimulation, which is due to the release of tachykinins from sensory nerves. Lung resistance was measured by airway resistance (RL) computed from airway and transpulmonary pressures and plasma exudation by measurement of Evans blue dye extravasation. Inhaled levcromakalim (25 mu g/ml) had a short duration of action, being effective against histamine-induced bronchoconstriction 2 min after pretreatment, but not at 10 min. Inhaled HOE 234 (25 mu g/ml) was similarly effective against histamine-induced bronchoconstriction but had a longer duration of action. Inhaled levcromakalim partially attenuated histamine-induced plasma extravasation in small airways, but not in the trachea or main bronchi, whereas inhaled HOE 234 had no effect. HOE 234 protected against non-adrenergic non-cholinergic nerve-induced bronchoconstriction, but had no effect on neurogenic- or substance P-induced plasma extravasation in the airway. Inhaled K+ channel openers protect against induced bronchoconstriction, but provide little or no protection against plasma exudation, possibly because of an increase in airway blood flow. In addition, inhaled HOE 234 had no effect on neurogenic leakage, suggesting that its vagal inhibitory effect on bronchoconstriction was on airway smooth muscle, rather than on release of neuropeptides from sensory nerves.

Loop diuretics inhibit cholinergic and noncholinergic nerves in guinea pig airways.

Furosemide, a loop diuretic, is known to inhibit the response to a variety of indirect bronchial challenges in humans but does not inhibit bronchoconstriction induced by inhaled methacholine or histamine. We have investigated the effects of the two loop diuretics, furosemide (10(-6) to 10(-3) M) and bumetanide (10(-7) to 10(-4) M), on airway smooth muscle contraction in vitro induced by electrical field stimulation (EFS), or exogenously applied acetylcholine (ACh) or substance P (SP) in guinea pig tracheal and bronchial smooth muscle strips pretreated with indomethacin (10(-5) M) and propranolol (10(-6) M). Both furosemide and bumetanide caused a concentration-dependent inhibition of cholinergically mediated neural contraction in the trachea. The effect of furosemide was not influenced by the presence of airway epithelium. Furthermore, both furosemide and bumetanide inhibited in a concentration-dependent fashion nonadrenergic, noncholinergic (NANC) contraction induced by electrical field stimulation of bronchi pretreated with atropine (10(-5) M). Neither drug at the highest concentration inhibited the responses to exogenous acetylcholine (10(-8) to 10(-2) M) or substance P (10(-9) to 10(-5) M). Thus loop diuretics inhibit the neurally induced contraction of guinea pig airways without a direct effect on airway smooth muscle. We conclude that loop diuretics inhibit both cholinergic and excitatory NANC neurotransmission in guinea pig airways and that this effect may be related to their inhibitory effects on the sodium-potassium-chloride cotransporter.

Mechanism of airway narrowing caused by inhaled platelet-activating factor. Role of airway microvascular leakage.

In order to study the mechanism of airway narrowing after inhaled platelet-activating factor (PAF) we measured concomitant changes in lung resistance (RL) and in airway microvascular leakage in anesthetized guinea pigs. RL and its recovery after hyperinflation at 5 min were measured until 6 min after PAF aerosol (0.1, 0.3, 1, and 3 mM), and in the case of 3 mM PAF also until 10 min. Microvascular leakage in trachea, main bronchi, and proximal and distal intrapulmonary airways was determined by measurement of extravasated Evans blue dye content. For comparison, the responses to inhaled histamine (3 mM) and 5-hydroxytryptamine (5HT) (3 mM), which act directly on airway smooth muscle, were also examined. Inhaled PAF increased RL dose-dependently, with a maximal response (peak RL) at 4 min after the inhalation, whereas the response to histamine or 5HT was maximal within a few seconds after the inhalation. Peak RL (cm H2O/ml/s) was significantly less after PAF (1.03 +/- 0.09) than after histamine (8.39 +/- 1.07) or 5HT (18.3 +/- 6.48), although there was no significant difference in RL after hyperinflation (recovery RL). No additional increase in RL was seen between 5 and 10 min after exposure. PAF caused a dose-dependent increase in Evans blue dye extravasation; 3 mM PAF induced significantly higher leakage than did histamine or 5HT at all airway levels at 6 min. PAF did not cause any additional extravasation of Evans blue dye at 10 min compared with that at 6 min after exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma exudation into airways induced by inhaled platelet-activating factor: effect of peptidase inhibition.

1. To evaluate whether endogenous peptide release is involved in the airway responses to inhaled platelet-activating factor, we measured lung resistance and airway microvascular leakage in anaesthetized guinea pigs pretreated with inhalation of either saline or a combination of the peptidase inhibitors phosphoramidon (0.1 mmol/l: 60 breaths; 7.5 nmol), to inhibit neutral endopeptidase, and captopril (4.6 mmmol/l: 60 breaths; 350 nmol), to inhibit angiotensin-converting enzyme. 2. Airway microvascular leakage was determined by the albumin marker Evans Blue dye injected intravenously (20 mg/kg) before platelet-activating factor or sham challenge. 3. Inhaled platelet-activating factor induced a maximum increase in lung resistance (1.43 +/- 0.33 cmH2O s-1 ml-1) which was not significantly different after pretreatment with phosphoramidon and captopril (1.44 +/- 0.21 cmH2O s-1 ml-1). 4. Inhalation of platelet-activating factor caused a significant increase in extravasated Evans Blue dye at all airway levels, an effect which was not potentiated by peptidase inhibition. Similar results were obtained with dye extravasated into the airway lumen and absorbed by a filter paper placed on the tracheal mucosa. Approximately 11% of the total tracheal dye was found in the lumen. There was a high correlation between tracheal tissue and tracheal lumen Evans Blue dye (r = 0.91; P less than 0.001). 5. We found a significantly lower dry to wet weight ratio in proximal intrapulmonary airways of animals exposed to platelet-activating factor, suggesting that platelet-activating factor caused airway oedema at this airway level.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dexamethasone and cyclosporin A on allergen-induced airway hyperresponsiveness and inflammatory cell responses in sensitized Brown-Norway rats.

We studied the effects of dexamethasone and cyclosporin A on the airway hyperresponsiveness (AHR) and the influx of inflammatory cells into the bronchoalveolar lavage (BAL) fluid seen 18 to 24 hr after exposure to aerosolized ovalbumin in actively ovalbumin-sensitized Brown-Norway rats. Allergen exposure resulted in an approximately sevenfold increase in bronchial responsiveness to inhaled acetylcholine associated with a significant increase in eosinophils and lymphocytes in BAL fluid. Dexamethasone (0.5 mg/kg administered intraperitoneally for 3 days) abolished the AHR and the increase in eosinophil and lymphocyte counts. However, cyclosporin A at two doses (5 and 50 mg given orally for 5 days) did not significantly prevent the induction of AHR while producing a significant inhibition of the eosinophil and lymphocyte influx. Dexamethasone (0.5 mg/kg for 3 days) or cyclosporin A (5 mg/kg for 5 days) on their own had no effect on airway responsiveness. We conclude that specific inhibition of T-lymphocyte activation in this Brown-Norway rat model is not sufficient to inhibit the induction of AHR despite suppressing allergen-induced eosinophilia in BAL fluid. However, corticosteroids, which have inhibitory effects on a wider range of inflammatory cells, are more effective. Our observations are in line with the potent effect of corticosteroids in airway inflammatory conditions such as asthma.

Airway hyperresponsiveness to acetylcholine and to tachykinins after respiratory virus infection in the guinea pig.

Upper respiratory tract virus infections may enhance airway responsiveness to histamine in normal subjects. We have studied the effects of parainfluenza Type I (Sendai) virus infection of the upper respiratory tract on the airway responsiveness to acetylcholine (ACh) and substance P administered by either the inhaled or intravenous route in the anesthetized guinea pig. Airway responses to electrical stimulation of the vagus nerves in the presence of atropine (1 mg.kg-1 i.v.) were also studied. After four to five days following virus infection, mean pulmonary insufflation pressure increased significantly in response to inhaled ACh compared to that in control animals. Responses to intravenous ACh were not enhanced. By contrast, responses to both intravenous and inhaled substance P were increased. In addition, mean pulmonary insufflation pressure after electrical stimulation of the vagus nerves for 30 seconds at 5 V, 5 msec (frequencies of 3, 10, and 30 Hz) were all enhanced after virus infection. We conclude that the increased airway responsiveness observed to the exogenous administration of the neurotransmitters ACh and substance P after viral respiratory infection may be due to different mechanisms possibly associated with an interference with the epithelium.

Induction of nitric oxide synthase in a model of allergic occupational asthma.

We have studied the induction of nitric oxide during late allergic responses, using a guinea pig model of trimellitic anhydride (TMA)-induced airway allergy. TMA is a low molecular weight chemical which can cause occupational asthma. The activity of nitric oxide synthase (NOS) was investigated by the detection of 3H-labeled citrulline formation from 3H-labeled arginine. In sensitized animals, challenge with TMA conjugated to guinea pigs albumin (TMA-GPSA) increased the activity of Ca(2+)-independent NOS (inducible NOS; iNOS) in lung and bronchial tissues at 15-17 h after challenge compared to nonsensitized animals. The induction of iNOS activity was associated with an associated with an increased level of nitrite, an end metabolite of the l-arginine-NO pathway, in bronchoalveolar lavage fluid. In contrast to iNOS, the activity of Ca(2+)-dependent NOS (constitutive NOS; cNOS) was not affected by the allergen challenge. These results demonstrate that iNOS in bronchial tissue is induced late after allergen challenge in sensitized guinea pig.

Characterization of allergen-induced bronchial hyperresponsiveness and airway inflammation in actively sensitized brown-Norway rats.

Bronchial responsiveness to inhaled acetylcholine (ACh) and inflammatory cell recruitment in bronchoalveolar lavage fluid (BALF) were studied in inbred Brown-Norway rats actively sensitized to, and later exposed to, ovalbumin (OA). We examined animals 21 days after initial sensitization at 18 to 24 hours, or 5 days after a single challenge, or after the last of seven repeated exposures administered every 3 days. BALF was examined as an index of inflammatory changes within the lung. Animals repeatedly exposed to OA aerosols had an increased baseline lung resistance and a significant increase in bronchial responsiveness to inhaled ACh compared to control animals at both 18 to 24 hours and 5 days after the last OA exposure. Sensitized animals receiving a single OA aerosol also demonstrated bronchial hyperresponsiveness (BHR) to inhaled ACh (p less than 0.01) at 18 to 24 hours of a similar order as the multiple-exposed group. There was a significant increase in eosinophils, lymphocytes, and neutrophils in BALF at 18 to 24 hours but not at 5 days after single or multiple exposure to OA aerosol in the sensitized groups. Control animals demonstrated no changes in bronchial responsiveness, although a small but significant increase in inflammatory cells was observed compared to saline-only treated animals. There was a significant correlation between bronchial responsiveness and eosinophil counts in the BALF in the single allergen-exposed group (Rs = 0.68; p less than 0.05). We conclude that (1) BHR after allergen exposure in sensitized rats is associated with the presence of pulmonary inflammation but persists despite the regression of inflammatory cells in BALF after multiple OA exposures, and (2) this rat model has many characteristics of human allergen-induced BHR.

Capsaicin pretreatment does not inhibit allergen-induced airway microvascular leakage in guinea pig.

We have studied the effects of tachykinin-depletion on airway microvascular leakage induced by allergen challenge in ovalbumin-sensitised guinea pigs. Tachykinin-depletion was obtained by capsaicin pretreatment 1 week before inhaled allergen challenge. Capsaicin pretreatment did not change airway microvascular permeability induced by allergen challenge. Thus, sensory neuropeptides may not be important in allergen-induced acute airway microvascular leakage in guinea pig in vivo.

Bronchoconstriction induced by inhaled sodium metabisulfite in the guinea pig. Effect of capsaicin pretreatment and of neutral endopeptidase inhibition.

Sodium metabisulfite (MBS), a commonly used preservative, induces bronchoconstriction in asthmatics, probably through the release of sulfur dioxide (SO2). The mechanisms involved in MBS- and SO2-induced bronchoconstriction are not yet certain. We aerosolized MBS or acid control solution (pH, 2.7) to anesthetized, tracheostomized guinea pigs pretreated intravenously with propranolol (1 mg/kg). MBS was given at increasing doubling concentrations (0.01, 0.02, 0.04, and 0.08 M) every 5 min. Steep concentration-response curves were observed, and most animals responded at 0.02 or 0.04 M. Tachyphylaxis was seen at high concentrations and during a subsequent MBS challenge 15 min later. For pharmacologic studies, we stopped the challenge when lung resistance (RL) had increased by at least 350%; a second challenge was found to be reproducible. MBS response was measured as the concentration needed to increase RL by 350% (PC350). Atropine (1 mg/kg given intravenously) did not affect PC350 or the peak RL response. Inhibition of neutral endopeptidase by inhaled phosphoramidon (7.5 nmol) administered before the repeated challenge did not alter PC350 value to MBS or peak RL responses (phosphoramidon, 201 +/- 49% of first peak; vehicle, 164 +/- 35%). In addition, the increase in RL was not prolonged in the phosphoramidon-treated group. Animals treated subcutaneously with capsaicin (50 mg/kg) 1 wk before the experiment, so as to deplete neuropeptides from airway sensory nerves, had PC350 values similar to those of the control animals. Our data demonstrate that inhaled MBS causes bronchoconstriction in guinea pigs by mechanisms that are due neither to a cholinergic reflex nor to the release of tachykinins from airway sensory nerves.

Bronchoconstriction and airway microvascular leakage in guinea pigs sensitized with trimellitic anhydride.

We have developed a guinea pig model of immediate airway responses following intradermal sensitization with free trimellitic anhydride (TMA). Guinea pigs were given an intradermal injection with either 0.1 ml of 0.3% TMA in corn oil (n = 8) or 0.1 ml of corn oil alone (n = 6). A guinea pig serum albumin conjugate of trimellitic anhydride (TMA-GPSA) was prepared with a substitution ratio of 21:1. All sensitized guinea pigs had raised specific serum IgG1 antibodies (ELISA), and IgE antibodies were detected in six of the eight sensitized guinea pigs by passive cutaneous anaphylaxis. On Days 21 to 28, guinea pigs were anesthetized, tracheostomized, and ventilated. Evans blue dye (20 mg/ml), an albumin marker, was injected intravenously to quantify airway microvascular leakage (MVL). TMA-GPSA (50 microliters; 1%) in saline was instilled into the trachea. Lung resistance (RL) was measured for 6 min. The guinea pigs were killed, and the lungs were removed. Peak RL (cm H2O/ml x s-1) was significantly increased in sensitized guinea pigs from 0.26 +/- 0.01, mean +/- SEM to 21.3 +/- 6.9 (p < 0.05), compared with nonsensitized guinea pigs. There was a significant increase in Evans blue at all levels of the tracheobronchial tree in sensitized guinea pigs compared with the controls (p < 0.005). The site of MVL was localized to the postcapillary venules as assessed by extravasation of intravascular Monastral blue dye. We conclude that intradermal sensitization of guinea pigs to TMA induces a polyclonal immune response, associated with bronchoconstriction and airway microvascular leakage, when challenged specifically with TMA-GPSA.(ABSTRACT TRUNCATED AT 250 WORDS)