Hydroxyurea inhibits airway hyperresponsiveness in guinea pigs by a granulocyte-independent mechanism

Exposure of guinea pigs to toluene diisocyanate (TDI) causes an increase in airway responsiveness to inhaled acetylcholine. This increased airway responsiveness is temporally associated with an increase in polymorphonuclear leukocytes (PMN) in the tracheal wall. To determine whether PMN play a mechanistic role in this increase in acetylcholine responsiveness, we studied the effects of PMN depletion on this response with 2 different cytotoxic drugs, hydroxyurea and cyclophosphamide. Airway responsiveness was measured in untreated, hydroxyurea-treated, or cyclophosphamide-treated animals while they breathed spontaneously or during mechanical ventilation through a tracheostomy. In untreated animals, exposure to TDI caused a significant increase in airway responsiveness to acetylcholine for both spontaneously breathing and anesthetized and ventilated animals. This TDI-induced increase in airway responsiveness was associated with a significant influx of PMN into both the extravascular and intravascular trachea. Treatment with hydroxyurea, to reduce PMN counts in the bloodstream to less than 200/mm3, inhibited both the TDI-induced increase in airway responsiveness and the TDI-induced influx of PMN into the trachea of both spontaneously breathing and mechanically ventilated animals. In mechanically ventilated animals, treatment with cyclophosphamide, until PMN counts in the bloodstream were less than 200/mm3, also inhibited the influx of PMN into the trachea but did not inhibit the TDI-induced increase in airway responsiveness. These results suggest that PMN are not necessary for the TDI-induced increase in airway responsiveness and that hydroxyurea inhibits this effect by a mechanism other than PMN depletion.     

The effect of endotoxin inhalation on airway responsiveness and cellular influx in rats

Studies in humans suggests that airway inflammation may modulate nonspecific airway responsiveness. We studied in a rat model the effect of the inhalation of endotoxin on the cellular composition of the bronchoalveolar lavage (BAL) fluid and airway responsiveness. The exposure to an aerosol of endotoxin caused a rapid influx of neutrophils in the airways. The neutrophils persisted up to 24 h after exposure. Elastase activity in lavage fluid became detectable 30 min after the endotoxin exposure and peaked 9 h later. The exposure to the endotoxin aerosol was followed 1 to 2 h later by a significant increase in the airway responsiveness to 5-hydroxytryptamine (5HT). However, the increase in responsiveness disappeared, and 9 to 12 h following the end of the exposure a significant decrease in airway 5HT responsiveness was observed at the moment that more than 80% of the cells contained in the BAL fluid were neutrophils. The effect of endotoxin on airway responsiveness and inflammation was dose dependent. We also compared in three different inbred rat strains the effect of endotoxin inhalation. The aerosol exposure induced in all three strains a comparable neutrophil influx in the airways, but only two of the three strains became hyperresponsive to 5HT. We conclude that the inhalation of endotoxin causes a neutrophilic airway inflammation in rats. The relationship between this airway inflammation and airway responsiveness is dependent on the time following the exposure and the animal strain used.     

Acute exposure to cigarette smoke induces airway hyperresponsiveness without airway inflammation in guinea pigs. Dose-response characteristics

We examined whether acute exposure to a low dose of cigarette smoke causes an increase in airway responsiveness in guinea pigs and whether the changes in airway responsiveness are accompanied by increased vascular permeability or neutrophil influx in the trachea. Animals were divided into four groups: groups exposed to 5, 10, or 20 puffs of cigarette smoke and a control group. Airway responsiveness was assessed by measuring specific airway resistance (SRaw) as a function of increasing concentration of inhaled methacholine (Mch) aerosol immediately, 5 h, and 24 h after exposure. In parallel studies, tracheal vascular permeability was quantified by measuring the tracheal extravasation of intravenously administered Evans blue dye, and neutrophil influx into the tracheal mucosa was quantified by counting cells within whole mounts of tracheas that were stained with Giemsa. Exposure to 5 puffs of cigarette smoke caused no changes in airway responsiveness. Exposure to 10 puffs induced airway hyperresponsiveness only immediately after exposure. Exposure to 20 puffs induced airway hyperresponsiveness not only immediately but also 5 h after exposure. There was a significant correlation between the dose (puffs) of cigarette smoke and increase in airway responsiveness immediately after exposure (r = 0.77; p less than 0.001). The tracheal extravasation of intravenously administered Evans blue dye and the number of neutrophils in the tracheal mucosa did not differ significantly from the corresponding control values at any time or in any exposed group. Furthermore, none of these changes was observed in the airways distal to the trachea of any animal immediately after exposure to 20 puffs of cigarette smoke.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of platelet activating factor antagonist on ozone-induced airway inflammation and bronchial hyperresponsiveness in guinea pigs.

We investigated the role of platelet-activating factor (PAF) in ozone-induced airway responses by examining the effects of L659,989, a potent PAF antagonist, on bronchial hyperresponsiveness and airway inflammation. Twenty-four male guinea pigs were studied in four equal groups. Total lung resistance (RL) in intubated and spontaneously breathing animals was measured in a constant-volume body plethysmograph. Dose-response curves to methacholine were determined in all animals at the start of the experiment. These were repeated on a separate day after the following types of treatments: air exposure in Group 1, intraperitoneally administered alcohol and air exposure in Group 2; intraperitoneally administered alcohol and ozone exposure in Group 3, and intraperitoneally administered L659,989 (a specific PAF antagonist), 5 mg/kg dissolved in alcohol, and ozone exposure in Group 4. Bronchoalveolar lavage (BAL) was performed after the second methacholine challenge, and the bronchial mucosa was also examined for inflammatory cells. Exposure to 3 ppm ozone for 2 h resulted in a three-doubling concentration increase in bronchial responsiveness, which was not significantly inhibited by prior treatment with L659,989. Ozone induced a 1.8-fold increase in BAL total cell count, increased eosinophilic influx into the airways, and increased eosinophilic infiltration in the bronchial mucosa, which were all not inhibited by L659,989 pretreatment. The results suggest that PAF may not have an essential role in ozone-induced airway hyperresponsiveness and nonallergic airway inflammation.     

A tachykinin receptor antagonist inhibits and an inhibitor of tachykinin metabolism potentiates toluene diisocyanate-induced airway hyperresponsiveness in guinea pigs

We have previously shown that tachykinin depletion or antagonism prevented the increase in airway responsiveness to inhaled acetylcholine caused by exposure to toluene diisocyanate (TDI) in awake guinea pigs. To insure that the effects of tachykinins were not limited to the extrathoracic airways and were not dependent on effects of TDI on baseline airway caliber, we determined airway responsiveness to acetylcholine inhaled through a tracheostomy in anesthetized and ventilated guinea pigs that were exposed to TDI or air after treatment with the tachykinin antagonist spantide, the tachykinin metabolism inhibitor phosphoramidon, or the vehicles for each drug. When these drugs were administered before and during TDI exposure, spantide significantly inhibited the TDI-induced increase in acetylcholine responsiveness and phosphoramidon significantly potentiated this effect, whereas neither drug altered acetylcholine responsiveness in air-exposed animals. To determine whether tachykinins were exerting their effect primarily during TDI exposure or during the subsequent acetylcholine challenge, we also examined the effect of each drug on acetylcholine responsiveness when the drugs were given after TDI exposure. At that time, spantide did not inhibit TDI-induced acetylcholine hyperresponsiveness and phosphoramidon did not potentiate it. Neither drug nor TDI increased pulmonary resistance measured through a tracheostomy in these anesthetized and ventilated animals. These results suggest that the TDI-induced increase in acetylcholine responsiveness is mediated by release of tachykinins into the intrathoracic airways during exposure to TDI.     

Prednisone inhibits late asthmatic reactions and the associated increase in airway responsiveness induced by toluene-diisocyanate in sensitized subjects

To determine whether late asthmatic reactions and the associated increase in airway responsiveness induced by toluene diisocyanate (TDI) are linked to airway inflammation, we investigated whether they are inhibited by prednisone. Ten "sensitized" subjects were studied in 2 sets of experiments. In the first set, each subject was given no treatment and was studied before and for 8 h after exposure to TDI. In the second set, 2 to 4 wk later, each subject was studied before treatment and then during treatment with prednisone (50 mg once a day for 3 days, orally), both before and after exposure to TDI. To assess late asthmatic reactions to TDI, we measured FEV1 immediately before and after exposure, then hourly for 8 h. To assess changes in airway responsiveness, we measured the provocation dose (mg) of methacholine causing a 20% decrease in FEV1 (PD20FEV1) before and 8 h after exposure to TDI. When the subjects received no prednisone treatment, TDI caused late asthmatic reactions and increased airway responsiveness. By contrast, when the subjects received prednisone, TDI caused no late asthmatic reaction or increased airway responsiveness. Prednisone did not change baseline airway caliber or airway responsiveness. These results suggest that late asthmatic reactions and the associated increase in airway responsiveness induced by TDI in "sensitized" subjects may depend on the development of a steroid-responsive acute inflammatory reaction within the airways.     

Ambient ozone concentrations induce airway hyperresponsiveness in some rat strains.

Ozone is known to induce airway hyperresponsiveness (AHR) in humans and animals. Previous studies in animals used high exposure levels and reported inconsistent results. The aim of this study was to investigate the effect of a single low-level ozone exposure on different inbred rat strains. Nine rat strains were exposed to 0.05 parts per million (ppm) for 4 h and airway responsiveness to intravenous 5-hydroxytryptamine (HT) examined. Bronchoalveolar lavage fluid (BALF) was examined for the presence of inflammatory cells and markers. Lewis, BDII and Long-Evans rats developed AHR 90 min after ozone exposure, whereas Wistar, Sprague-Dawley, Fisher 344, Brown-Norway, BDE and DA rats did not. Baseline airway responsiveness to 5-HT differed significantly between rat strains, but did not correlate with the presence or absence of ozone-induced AHR. No inflammatory cell influx was found in BALF of any rat strain. In Long-Evans rats, AHR lasted up to 12 h after ozone exposure despite the absence of an inflammatory cell influx or increase in lactate dehydrogenase, alkaline phosphatase or total protein in BALF. In conclusion, exposure to an ambient concentration of ozone induced airway hyperresponsiveness without airway inflammation in some highly inbred rat strains. Genetic factors are likely to account for the observed variability in sensitivity of the airways to ozone.     

Apparent effect of catalase on airway edema in guinea pigs. Role of endotoxin contamination

The airway edema that develops in guinea pigs after exposure to toluene diisocyanate (TDI) requires the presence of polymorphonuclear leukocytes (PMN). To determine whether this airway edema is mediated by the release of hydrogen peroxide from PMN, we treated animals intravenously with catalase bound to polyethylene glycol and examined the extravasation of Evans blue dye into the tracheal wall after exposure to air or 3 ppm TDI for 1 h. Catalase (25,000, 100,000, and 300,000 IU/kg) caused a dose-dependent inhibition of the TDI-induced increase in dye extravasation. However, treatment with catalase, inactivated at the peroxide binding site with 3-aminotriazole, inhibited dye extravasation after exposure to TDI as effectively as the equimolar 100,000 IU/kg dose of active catalase. Injection of polyethylene glycol alone was without effect. Dose-dependent decreases in extravascular migration of PMN and in circulating PMN also were noted after catalase treatment. These results suggest that the catalase preparations used in these studies inhibited the PMN-dependent airway edema by an effect other than hydrogen peroxide scavenging. Examination of this and other commercially available catalase preparations revealed trace concentrations of endotoxin at levels that could be responsible for the observed effects on PMN function. Treatment of animals with doses of Escherichia coli endotoxin similar to those inadvertantly administered to the catalase-treated groups (0.1 ng/kg to 100 ng/kg, intravenously) inhibited TDI-induced extravasation of Evans blue dye in a dose-dependent manner. These results suggest that contaminating endotoxin may contribute to some of the protective effects of preparations of catalase observed in previous studies of vascular permeability.     

Interaction between SO2 and cold-induced bronchospasm in anesthetized rabbits

In anesthetized, paralyzed and artificially ventilated rabbits, reflex changes in lung resistance induced by cooling the inspired air from 38 to 15 degrees C were studied before and after 45 min periods of SO2 exposure at two different concentrations (0.5 or 5 ppm). Both concentrations of SO2 induced significant increase in RL in intact animals (+16% and +50%, respectively). The effect of 5 ppm SO2 persisted after vagotomy. The cold-induced bronchospasm was halved after exposure to 0.5 ppm SO2 and was no longer significant after exposure to 5 ppm SO2. In both cases, RL recovered to control values 40 min after the end of SO2 exposure and then, the magnitude of cold-induced bronchospasm also recovered. The reflex bronchoconstrictor response to phenyldiguanide (PDG) i.v. disappeared after exposure to 5 ppm SO2. However, the bronchomotor response to histamine i.v., which involved both reflex and direct actions on airway smooth muscle, was not altered. These results show that (1) prolonged increase in RL measured after SO2 exposure does not result from a vagal reflex; (2) the cold-induced bronchospasm, as well as the bronchomotor response to PDG, are reduced or suppressed during the period where the effect of SO2 persisted. This suggests that 45 min exposure to SO2 induces transient alterations in tracheobronchial wall, which reduce the accessibility to nervous receptors in the airways.     

Ozone-induced bronchial hyperresponsiveness in the rat is not accompanied by neutrophil influx or increased vascular permeability in the trachea

We determined whether ozone-induced bronchial hyperresponsiveness in the rat is accompanied by neutrophil influx or increased vascular permeability in the trachea. Three groups of female Long-Evans rats were studied. One group was exposed to 4 ppm ozone for 2 h and studied immediately thereafter, another group was similarly exposed but was not studied until 24 h after the ozone exposure, and a third group consisted of control rats that breathed room air. Increases in total pulmonary resistance caused by acetylcholine aerosol were measured to assess bronchial responsiveness in these 3 groups. In parallel studies, neutrophil influx into the tracheal mucosa was quantified by counting cells within whole mounts of tracheas that were treated histochemically to stain the myeloperoxidase in neutrophils, and tracheal vascular permeability was quantified by measuring the amount of Evans blue dye extravasated into the trachea. In the rats studied immediately after the ozone exposure, the concentration of acetylcholine required to increase total pulmonary resistance to three-fold the baseline value was only 6% of that required in the controls. In the rats studied 24 h after the ozone exposure, this provocative acetylcholine concentration was not significantly different from that of the controls. Neither the number of neutrophils in the tracheal mucosa nor the amount of Evans blue dye extravasated into the trachea was significantly different from the corresponding control values at either time. We conclude that rats exposed to ozone develop bronchial hyperresponsiveness without detectable neutrophil influx or increased vascular permeability in the trachea.     

Tachykinins mediate the acute increase in airway responsiveness caused by toluene diisocyanate in guinea pigs

Exposing guinea pigs to toluene diisocyanate (TDI) causes an acute increase in airway responsiveness to inhaled acetylcholine. The mechanism of this increase in airway responsiveness is unknown. Capsaicin-sensitive afferent nerves and the tachykinins they release upon activation are important in controlling bronchomotor tone in guinea pigs. To determine whether tachykinins are important in TDI-induced airway hyperresponsiveness, we studied the effects of tachykinin depletion, using capsaicin, and competitive tachykinin antagonism, using (D-Arg1, D-Pro2, D-Trp7.9, Leu11) substance P, on TDI-induced airway hyperresponsiveness. In 9 of 9 untreated animals, TDI exposure caused a large and significant increase in airway responsiveness to acetylcholine. The mean concentration of acetylcholine required to decrease specific airway conductance by 50% below baseline (the PD50) was 1.51% before TDI exposure and 0.17% after TDI exposure (p less than 0.0005). Capsaicin treatment had no effect on the PD50 but prevented the TDI-induced increase in airway responsiveness in 10 of 12 animals. (The PD50 was 1.03% before TDI and 1.27% after TDI exposure.) Treatment with the tachykinin antagonist (D-Arg1, D-Pro2, D-Trp7.9, Leu11) substance P also abolished the TDI-induced increase in airway responsiveness in all 5 animals treated. Although TDI exposure also causes airway edema, the effect of capsaicin treatment on TDI-induced airway hyperresponsiveness did not result from prevention of airway edema. TDI exposure caused a marked increase in tracheal extravasation of intravenously administered Evans blue dye that was not prevented by capsaicin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of exposure to 500 ppm sulfur dioxide on the lungs of the ferret

Male ferrets (Mustela putorius furo) were exposed 3 h/day, 3 days/week for 12 weeks to 500 ppm SO2. Determinations were made of airway responsiveness by producing histamine dose-effect curves. Lung tissues were fixed and studied by light and electron microscopy. Epithelial cells of the trachea and bronchus were most affected. Lesions observed included changes in ciliated cells, edema and cell infiltration. The most responsive animals to histamine were 2 from the exposed group. Nasal discharge and dried mucus were observed after 3 days of exposure. Coughing was first noted after 2 weeks. Results favor further pursuit of the use of the ferret as a model for human airways disease.     

Lymphokine-induced airway hyperresponsiveness in the rat

We evaluated the potential role of the lymphocyte in chronic airway inflammation and responsiveness by repeated administration to rats of interleukin-2 (IL-2), the principal lymphokine responsible for lymphocyte proliferation. Lewis rats (mean weight, 184 +/- 2 g) received either 120,000 units of IL-2 (n = 10) or vehicle (n = 7) subcutaneously twice a day for 4.5 days. Animals were anesthetized with urethane and intubated for measurements of pulmonary resistance (RL) and airway responsiveness to aerosol methacholine (MCh). Lung lavage was performed, the animals were exsanguinated, and the lungs were fixed in 10% formalin. Histologic edema and the extent of infiltration of the bronchi, pulmonary veins, and arteries by cells was scored blindly. IL-2 increased airway responsiveness to MCh; the concentrations of MCh causing a doubling of RL were 0.14 versus 1.39 mg/ml (geometric mean) for the IL-2 and vehicle group, respectively (p = 0.001). IL-2 significantly increased total cellular return and the percentage of lymphocytes, neutrophils, and eosinophils in lavage. IL-2 caused edema and a mixed cellular infiltration of the bronchovascular tree. Lymphocytes predominated around the airways and veins. A correlation (r = 0.50) was present between airway responsiveness and airway inflammation but not with edema or vascular infiltration. Release of IL-2 by lymphocytes in the airways may be an important mediator of airway hyperresponsiveness.     

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)     

Combined effects of ozone and cigarette smoke on airway responsiveness and vascular permeability in guinea pigs

The effects of combined exposure to ozone and cigarette smoke on airway responsiveness and tracheal vascular permeability, compared with those of single exposure were examined in guinea pigs. Airway responsiveness was assessed by measuring the specific airway resistance (sRaw) as a function of increasing concentration of inhaled methacholine aerosol immediately, 5 hr, and 24 hr after exposure. In a parallel study, tracheal vascular permeability was quantified by measuring the tracheal extravasation of intravenously administered Evans blue dye. Neither exposure to 1 ppm ozone for 30 min nor 5 puffs of cigarette smoke increased airway responsiveness or vascular permeability at any time after exposure. Combined exposure to 1 ppm ozone for 30 min and 5 puffs of cigarette smoke caused airway hyperresponsiveness and increased vascular permeability immediately after exposure. Exposure to 1 ppm ozone for 90 min increased both airway responsiveness and vascular permeability immediately after exposure. Exposure to 10 puffs of cigarette smoke increased airway responsiveness but not vascular permeability immediately after exposure. Combined exposure to 1 ppm ozone for 90 min and 10 puffs of cigarette smoke increased both airway responsiveness and vascular permeability immediately after exposure. The combined exposure to ozone and cigarette smoke thus increased both airway responsiveness and tracheal vascular permeability to a greater extent than did exposure to a single agent, suggesting that a combination of air pollutants has a more deleterious effect both on airway responsiveness and on tracheal vascular permeability than does either agent alone in guinea pigs. Offprint requests to: T. Okubo     

Effect of vitamin C on NO2-induced airway hyperresponsiveness in normal subjects. A randomized double-blind experiment

We conducted a double-blind randomized study to determine the effect of vitamin C on NO2-induced airway hyperresponsiveness in normal subjects. Eleven normal subjects were randomly assigned an order for 4 experimental exposures. For each exposure, subjects took either vitamin C (500 mg 4 times a day for 3 days) or placebo followed by exposure either to clean air or to 2.0 ppm NO2. Measurements of lung mechanics and airway responsiveness to methacholine aerosol were obtained. Serum level of ascorbic acid was determined before each exposure. NO2 exposure with placebo resulted in significant enhancement of airway responsiveness to methacholine aerosol (air-placebo 64 +/- 7 to NO2-placebo 53 +/- 8 mg/ml). Pretreatment with ascorbic acid prevented the significant alteration in airway responsiveness to methacholine aerosol (65 +/- 13 mg/ml, p less than 0.04). These results suggest that airway hyperresponsiveness induced by NO2 in normal subjects is completely prevented by pretreatment with ascorbic acid.     

Tumor necrosis factor receptor 2 contributes to ozone-induced airway hyperresponsiveness in mice

The purpose of this study was to determine whether tumor necrosis factor (TNF) contributes to airway hyperresponsiveness (AHR) and migration of polymorphonuclear leukocytes (PMN) into the airways following exposure to ozone (O(3)). Wild-type mice, TNF p55 or p75 receptor knockout mice (p55 TNFR -/- and p75 TNFR -/-), as well as double receptor knockout mice (p55/p75 TNFR -/-), were exposed to O(3). Three hours after cessation of O(3), airway responses to inhaled methacholine were determined by whole body plethysmography using changes in enhanced pause (Penh) as an index of airway narrowing. In wild-type mice, O(3) exposure (0.5 ppm, 3 h) caused a significant increase in airway responsiveness as indicated by a 1.2 log leftward shift in the methacholine dose- response curve. In contrast, in p55/p75 TNFR -/- mice, O(3) caused only a 0.5 log shift in the dose-response curve (p < 0.05 compared with wild-type). Similar results were obtained in p75 TNFR -/- mice. In contrast, O(3)-induced airway hyperresponsiveness was not different in WT and p55 TNFR -/- mice. During O(3) exposure (1 pm, 3 h), minute ventilation (V E) decreased by 64 +/- 4% in wild-type, but only 24 +/- 5% in p55/p75 TNFR -/- mice, indicating that despite their reduced O(3)-induced AHR, the TNFR-deficient mice actually inhaled a greater dose of O(3). Similar results were obtained in p75 -/- mice, whereas changes in V E induced by O(3) were the same in wild-type and p55 -/- mice. PMN numbers in bronchoalveolar lavage fluid recovered 21 h after cessation of exposure to O(3) (2 ppm, 3 h) were significantly increased compared with after air exposure but were not different in wild-type and p55/p75 TNFR -/- mice. Our results indicate that TNF contributes to the AHR but not the PMN emigration induced by acute O(3) exposure. Keywords: whole body plethysmography; polymorphonuclear leukocytes; minute ventilation; knockout mice; methacholine     

Ozone exposure suppresses epithelium-dependent relaxation in feline airway

We examined the effect of exposure to ozone on the epithelium-dependent relaxation (EpDR) of bronchioles evoked by electrical field stimulation (EFS) in a feline model with hyperresponsive airways induced by exposure to ozone. Airway responsiveness was assessed by measuring the increases in total pulmonary resistance (RL) produced by aerosolized acetylcholine (ACh) in vivo. Airway responsiveness was also measured in vitro in dissected bronchiolar ring preparations. Exposure to ozone (3 ppm, 2 h) significantly increased the airway responsiveness in vivo. The concentration of ACh required increasing R _L to 200% of the baseline value, decreased from 1.97 mg/ml (GSEM 1.94) to 0.12 mg/ml (GSEM 1.77, p < 0.01) after exposure to ozone. EFS evoked atropine-, guanethidine-, and tetrodotoxin-resistant relaxations in the control bronchiolar rings precontracted by 5-hydroxytryptamine. Such relaxation was significantly suppressed by the mechanical denudation of epithelium, confirming that it was epithelium dependent. The amplitude of EpDR was significantly suppressed in the animals exposed to ozone. These results suggest that EpDR is present in cats, and that its inhibition may contribute to the development of airway hyperresponsiveness.Offprint requests to: H. Aizawa     

Indomethacin inhibits the airway hyperresponsiveness but not the neutrophil influx induced by ozone in dogs

To determine whether oxygenation products of arachidonic acid may be involved in the airway hyperresponsiveness induced by ozone exposure, we studied whether ozone-induced hyperresponsiveness could be inhibited by the prostaglandin synthetase inhibitor, indomethacin, in dogs. Airway responsiveness was assessed with dose-response curves of acetylcholine aerosol versus pulmonary resistance in 2 sets of experiments: in one set, 5 dogs were given no indomethacin treatment and were studied both before and after ozone exposure (3.0 ppm, 2 h); in another set, the same dogs were studied before indomethacin treatment or ozone exposure and then during treatment (1 mg/kg every 12 h for 4 days) both before and after ozone exposure. On each occasion, we also determined the number of neutrophils in biopsies of the airway epithelium. When the dogs were not treated with indomethacin, ozone caused a marked increase in responsiveness to acetylcholine and a marked increase in the number of neutrophils in the airway epithelium. When the dogs were given indomethacin, responsiveness was no different during treatment than before treatment, but more importantly, responsiveness did not increase significantly after they were exposed to ozone. Interestingly, indomethacin treatment did not affect either the baseline number of epithelial neutrophils before ozone exposure or the increase in the number of neutrophils after exposure. The results suggest that oxygenation products of arachidonic acid that are sensitive to inhibition by indomethacin play a role in ozone-induced hyperresponsiveness without affecting the influx of neutrophils.     

Short-term exposure to 0.3 ppm nitrogen dioxide does not potentiate airway responsiveness to sulfur dioxide in asthmatic subjects

Whether short-term exposure to low levels of nitrogen dioxide (NO2) enhances airway responsiveness in asthmatic subjects is controversial. Because it is well established that asthma is associated with increased airway responsiveness to another common air pollutant, sulfur dioxide (SO2), we examined whether short-term exposure of asthmatic subjects to 0.3 ppm NO2 potentiates airway responsiveness to inhaled SO2. We exposed nine subjects with clinically stable asthma to 0.3 ppm NO2 or filtered air in an environmental room for 30 min on 2 separate days at least 1 wk apart in a double-blind, randomized fashion. A questionnaire about common symptoms related to inhaled irritants was completed before and immediately after each exposure. Each subject exercised (60 to 80 W) on a cycloergometer during the first 20 min of each exposure. We measured specific airway resistance (SRaw) and FEV1/FVC before, 5 min after, and 1 h after completion of the air or NO2 exposure. The single-breath nitrogen test (SBN2) was also performed before and 1 h after completion of the air or NO2 exposures and closing volume was determined; subsequently, SO2 dose-response curves (0.25 to 4.0 ppm) were performed via a mouthpiece. Each dose of SO2 was inhaled at a minute ventilation of 20 L/min for 4 min and was doubled until SRaw increased by at least 8 U above baseline. The dose of SO2 required to provoke an increase in SRaw of 8 U above baseline was determined by linear interpolation from the dose-response curve (PD8Uso2).(ABSTRACT TRUNCATED AT 250 WORDS)