Inhalation of adenosine 5'-monophosphate increases methacholine airway responsiveness

Airway hyperresponsiveness is a characteristic feature in asthmatic subjects, but the mechanism of the hyperresponsiveness is not known. The purpose of this study was to investigate whether methacholine airway responsiveness was increased 24 h after inhalation of adenosine 5'-monophosphate (AMP). Ten atopic asthmatic subjects and six atopic normal subjects were studied on 4 study days. On the 1st day, a methacholine inhalation test was performed, followed within 48 h by an AMP inhalation test. Seven days later the second AMP test was performed, and 24 h later the methacholine inhalation test was repeated. Response was measured using partial flow-volume curves, and the concentration required to cause a 40% fall in the partial flow-volume curve (PC40) was calculated. The geometric mean methacholine PC40 fell from 1.36 mg/ml on day 1 (before AMP inhalation) to 0.71 mg/ml on day 4 (24 h after AMP inhalation, P less than 0.01). There was no change in the mean PC40 for adenosine on the 2 study days (5.82 and 7.06 mg/ml, P greater than 0.1). These findings suggest that adenosine release may contribute to the increase in airway responsiveness after allergen challenge.     

Development of chronic airway hyperresponsiveness in ragweed-sensitized dogs

We studied dogs neonatally sensitized to ragweed and their littermate controls at 4, 6, 8, 10, 12, and 15 mo of age. Acute allergic airway response to inhalation of ragweed in the sensitized dogs was marked (greater than 12-fold increase from base line) and reproducible at all times. Nonallergic airway responsiveness, measured as the concentration of acetylcholine required to increase airway resistance by 5 cmH2O.l-1.s (PC5), increased in sensitized and decreased in nonsensitized dogs from 4 to 15 mo of age (P less than 0.01). Before antigen, at 12 and 15 mo, sensitized dogs were significantly (P less than 0.05) more responsive to acetylcholine than controls. Six hours after antigen, sensitized dogs were 11-fold more responsive (P less than 0.005) than controls at those times. More eosinophils and mast cells and fewer macrophages (P less than 0.05) were present in bronchoalveolar lavage (BAL) from 12- and 15-mo-old sensitized dogs than their controls. BAL fluid histamine was higher (P less than 0.05) in sensitized than control dogs. Regression analysis revealed r = -0.75 (P = 0.003) between BAL mast cells and PC5 in sensitized dogs and R2 = 0.89 for PC5 and BAL mast cells, macrophages, and eosinophils. Neonatally sensitized dogs represent an excellent animal model in which to study the pathophysiology of asthma.     

Antigen-induced airway hyperresponsiveness and pulmonary inflammation in allergic dogs

We studied whether antigen-induced airway hyperresponsiveness was associated with pulmonary inflammation in 11 anesthetized ragweed-sensitized dogs. Airway responsiveness to acetylcholine aerosol was determined before and at 2, 6, and 24 h after ragweed or sham aerosol challenge. Pulmonary inflammation was assessed by bronchoalveolar lavage (BAL) performed at either 2 or 6 h. Total pulmonary resistance increased 11-fold at 5 min after ragweed. Airway responsiveness was unchanged at 2 h but was increased 6.6-fold at 6 h in 8 of 11 dogs (P less than 0.001); hyperresponsiveness persisted from 4 days to 4 mo. Airway responsiveness was unchanged by aerosols of diluent. Neutrophils in BAL fluid increased approximately sixfold at 2 h (P less than 0.02) and at 6 h (P less than 0.02) after antigen challenge. There were fewer eosinophils in fluid recovered at 6 h after antigen compared with 2 h lavages (P less than 0.05). In three nonresponders, BAL showed no significant changes in neutrophils and eosinophils after antigen. Thus antigen-induced hyperresponsiveness is associated with the presence of pulmonary inflammation, presumably arising from the airways and involving both neutrophils and eosinophils.     

Allergen-induced increase in airway responsiveness and inflammation in mild asthma

The relationship between airway responsiveness to methacholine and inflammatory cells in bronchoalveolar lavage (BAL) was determined in patients with history of rhinitis and/or mild bronchial asthma either at baseline (10 patients) or 3-4 h after allergen inhalation challenge (11 patients). At baseline, airway responsiveness did not correlate with any BAL cell population. When data obtained after allergen challenge were included in the analysis, 44% of the variability of airway responsiveness was explained by a multiple regression model with BAL eosinophils as a directly correlated (P = 0.002) independent variable and with BAL macrophages as an inversely correlated (P = 0.045) independent variable. Changes in airway responsiveness after allergen challenge were predicted (82% of variance explained) by a model with BAL eosinophils and BAL lymphocytes as directly correlated (P = 0.0002 and P = 0.03, respectively) independent variables. We conclude that, in stable asymptomatic asthma, baseline airway responsiveness does not correlate with the presence in the airways of inflammatory and immunoeffector cells that can be recovered by BAL. Nevertheless the allergen-induced increase in airway responsiveness is associated with an influx of eosinophils and lymphocytes in the bronchial lumen.     

Intrinsic and antigen-induced airway hyperresponsiveness are the result of diverse physiological mechanisms.

Airway hyperresponsiveness (AHR) is a defining feature of asthma. We have previously shown, in mice sensitized and challenged with antigen, that AHR is attributable to normal airway smooth muscle contraction with exaggerated airway closure. In the present study we sought to determine if the same was true for mice known to have intrinsic AHR, the genetic strain of mice, A/J. We found that A/J mice have AHR characterized by minimal increase in elastance following aerosolized methacholine challenge compared with mice (BALB/c) that have been antigen sensitized and challenged [concentration that evokes 50% change in elastance (PC(50)): 22.9 +/- 5.7 mg/ml for A/J vs. 3.3 +/- 0.4 mg/ml for antigen-challenged and -sensitized mice; P < 0.004]. Similar results were found when intravenous methacholine was used (PC(30) 0.22 +/- 0.08 mg/ml for A/J vs. 0.03 +/- 0.004 mg/ml for antigen-challenged and -sensitized mice). Computational model analysis revealed that the AHR in A/J mice is dominated by exaggerated airway smooth muscle contraction and that when the route of methacholine administration was changed to intravenous, central airway constriction dominates. Absorption atelectasis was used to provide evidence of the lack of airway closure in A/J mice. Bronchoconstriction during ventilation with 100% oxygen resulted in a mean 9.8% loss of visible lung area in A/J mice compared with 28% in antigen-sensitized and -challenged mice (P < 0.02). We conclude that the physiology of AHR depends on the mouse model used and the route of bronchial agonist administration.     

A PAF antagonist blocks antigen-induced airway hyperresponsiveness and inflammation in sheep

We studied the effects of WEB-2086, a specific antagonist of platelet-activating factor (PAF), on the development of antigen-induced airway hyperresponsiveness and inflammation in sheep (n = 8). For these studies, airway responsiveness was determined from slopes of carbachol dose-response curves (DRC) performed at base line (prechallenge) and 2 h after Ascaris suum antigen challenges in the following three protocols: 1) antigen challenge alone (control trial), 2) WEB-2086 (1 mg/kg iv) given 30 min before antigen challenge (WEB pretreatment), and 3) WEB-2086 given 2 h after antigen challenge, immediately before the postchallenge DRC (WEB posttreatment). Airway inflammation was assessed by bronchoalveolar lavage (BAL) before antigen challenge and after the postchallenge DRC for each trial. A. suum challenge resulted in acute increases in specific lung resistance that were not different among the three trials. Antigen challenge (control trial) caused a 93% increase (P less than 0.05) in the slope of the carbachol DRC when compared with the prechallenge value. WEB pretreatment (1 mg/kg) reduced (P less than 0.05) this antigen-induced hyperresponsiveness, whereas pretreatment with a 3-mg/kg dose completely prevented it. WEB posttreatment was ineffective in blocking this hyperresponsiveness. BAL neutrophils increased after antigen challenge in the control trial and when WEB-2086 was given after antigen challenge (P less than 0.05). Pretreatment with WEB-2086 (1 or 3 mg/kg) prevented this neutrophilia. This study provides indirect evidence for antigen-induced PAF release in vivo and for a role of endogenous PAF in the modulation of airway responsiveness and airway inflammation after antigen-induced bronchoconstriction in sheep.     

Inhaled PAF fails to induce airway hyperresponsiveness to methacholine in normal human subjects

The effects of three increasing doses of platelet-activating factor (PAF) on airway caliber and methacholine bronchial responsiveness were studied. On separate occasions nine normal subjects inhaled a single cumulative provocation concentration of methacholine (control) causing a 40% fall (PC40 Vp30) in maximum expiratory flow rate at 70% of base-line vital capacity below total lung capacity during a partial forced expiratory maneuver or 100 or 200 micrograms PAF, and seven subjects inhaled a further dose of 400 micrograms PAF. Methacholine responsiveness was measured before, at 3 and 7 h, then on days 1, 2, 3, 4, 7, 10, and 14 after each challenge. The maximum falls in Vp30 appeared dose dependent, but a significant difference between the magnitude of the responses was only observed between the 400- and 100-micrograms PAF dose (P less than 0.05). During the control period repeated methacholine challenges resulted in a progressive increase in cumulative provocation concentration of an agonist causing a 20% fall in forced expiratory volume in 1 s from base line, reaching significance on days 1 and 2 (2.44- and 2.4-fold of base line, respectively, P less than 0.01) before returning to base line on day 7. No difference was seen in methacholine responsiveness after any of the three doses of PAF compared with that after the control. We conclude that PAF causes dose-dependent bronchoconstriction but does not change airways responsiveness to methacholine and that repeated high-dose methacholine challenge leads to loss of responsiveness to this agonist.     

Differences in airway responsiveness to leukotriene D4 in allergic sheep with and without late bronchial responses

Allergic sheep respond to inhaled Ascaris suum antigen with either acute and late bronchial obstructions (dual responders) or only acute bronchoconstriction (acute responders). In this study we tested the hypothesis that one factor which may distinguish between these two populations is the difference in sensitivity to a specific mediator of airway anaphylaxis, leukotriene (LT) D4 (a major component of slow reacting substance of anaphylaxis). We postulated that if the hypothesis was correct then dual responders should demonstrate increased airway responses to inhaled LTD4 and that this increased responsiveness should also be reflected by a more severe response to inhaled antigen. To test this we used animals from both groups with the same degree of non-specific airway responsiveness to carbachol and determined their airway responses to controlled inhalation challenges with synthetic LTD4 and Ascaris suum antigen. Airway responsiveness to carbachol was determined by measuring the change in specific lung resistance (SRL) to increasing concentrations of carbachol aerosol, and then identifying, by linear interpolation, the provocative carbachol concentration which produced a 150% increase (PC150) in SRL. Airway responses to LTD4, and antigen were determined by measuring the percentage change in SRL after a controlled inhalation challenge with either aerosol. Airway responsiveness to carbachol was not different between the two groups. There was, however, a difference (p less than 0.05) in the airway response to the same dose of LTD4 in the two groups. Dual responders showed a 297 +/- 72% increase in SRL as compared to a 90 +/- 13% increase in SRL in the acute responders. Dual responders also showed a greater immediate and more prolonged response to antigen than did acute responders. These results suggest that increased responsiveness to LTD4 may be one factor which may distinguish dual responders from acute responders.     

Immunologic and nonimmunologic responsiveness in ragweed-sensitized dogs

The relationship between airway responsiveness to inhaled antigen and histamine, immunologic release of lung histamine, immunologic responsiveness of skin, and specific immunoglobulin E (IgE) antibodies were examined in 11 inbred allergic dogs immunized with extracts of ragweed and grass and 5 nonimmunized control dogs from the same colony. Airway responsiveness to antigen and histamine was characterized by the doses that increased the airflow resistance of the total respiratory system to twice the control values (ED200). Highly significant correlations were found between airway responsiveness and cutaneous responsiveness to antigen and other immunologic characteristics (e.g., IgE and histamine released from lung by inhaled antigen) in all dogs. In ragweed-sensitized dogs, there was an inverse correlation between immunologic responsiveness (reflected by the cutaneous response to antigen and histamine released from lung by inhaled antigen) and nonimmunologic responsiveness of airways (histamine ED200: r = 0.73, P less than 0.05 and r = 0.75, P less than 0.01, respectively). Antigen ED200 was also correlated with histamine release from lung after antigen inhalation (r = 0.74; P less than 0.01). We conclude that airway reactions to inhaled antigen in allergic dogs are dependent not only on immunologic factors but also on the degree of nonimmunologic airway responsiveness to histamine and that these factors are correlated inversely.     

Circadian rhythm in airway responsiveness and airway tone in patients with mild asthma.

To determine the characteristics and reproducibility of circadian rhythms of airway responsiveness to histamine and methacholine and their relationship to airway tone in patients with mild asthma, we studied nine subjects with complaints of nighttime awakening due to dyspnea and/or cough at least once a week. Their mean age was 31.4 yr (range 17-65) and their mean daytime FEV1 was 99 +/- 14 (SD) % predicted. Forced expiratory volume in 1 s (FEV1) and the provocative concentrations of histamine and methacholine necessary to decrease FEV1 by 20% (PC20FEV1) were determined every 4 h for 13 consecutive measurements. Three subjects were measured with histamine, three with methacholine, and three with both histamine and methacholine. Data were evaluated on an individual basis. PC20FEV1 to histamine and methacholine showed significant and reproducible circadian variations in all cases (P less than 0.01 each) with a mean amplitude of 1.00 +/- 0.17 (SD) doubling concentrations for histamine and 1.35 +/- 0.29 doubling concentrations for methacholine. The amplitude of PC20FEV1 was significantly larger (P less than 0.05) and the time of maximum responsiveness was significantly earlier (P less than 0.05) with methacholine compared with histamine. FEV1 showed significant (P less than 0.05) circadian variations in three of nine subjects, and peak expiratory flow rate showed variations in two subjects. Correlation between the variations of FEV1 and PC20FEV1 was significant (P less than 0.05) in 5 of 12 cases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Airway responsiveness to methacholine: effects of deep inhalations and airway inflammation.

We determined the dose-response curves to inhaled methacholine (MCh) in 16 asthmatic and 8 healthy subjects with prohibition of deep inhalations (DIs) and with 5 DIs taken after each MCh dose. Flow was measured on partial expiratory flow-volume curves at an absolute lung volume (plethysmographically determined) equal to 25% of control forced vital capacity (FVC). Airway inflammation was assessed in asthmatic subjects by analysis of induced sputum. Even when DIs were prohibited, the dose of MCh causing a 50% decrease in forced partial flow at 25% of control FVC (PD(50)MCh) was lower in asthmatic than in healthy subjects (P < 0.0001). In healthy but not in asthmatic subjects, repeated DIs significantly decreased the maximum response to MCh [from 90 +/- 4 to 62 +/- 8 (SD) % of control, P < 0.001], increased PD(50)MCh (P < 0.005), without affecting the dose causing 50% of maximal response. In asthmatic subjects, neither PD(50)MCh when DIs were prohibited nor changes in PD(50)MCh induced by DIs were significantly correlated with inflammatory cell numbers or percentages in sputum. We conclude that 1) even when DIs are prohibited, the responsiveness to MCh is greater in asthmatic than in healthy subjects; 2) repeated DIs reduce airway responsiveness in healthy but not in asthmatic subjects; and 3) neither airway hyperresponsiveness nor the inability of DIs to relax constricted airways in asthmatic subjects is related to the presence of inflammatory cells in the airways.     

Indomethacin and FPL-57231 inhibit antigen-induced airway hyperresponsiveness in sheep

We compared the development of antigen-induced airway hyperresponsiveness (AHR) 24 h after challenge with Ascaris suum antigen in allergic sheep with acute (n = 7) and with dual (n = 7) airway responses and then attempted to modify this AHR. Cholinergic airway responsiveness was determined by measuring the carbachol dose required to increase specific lung resistance (sRL) 150% (i.e., PC150). Subsequently the sheep were challenged with antigen and sRL was measured at predetermined times to document the presence or absence of a late response. PC150 was redetermined 24 h later followed by bronchoalveolar lavage (BAL) to assess inflammation. Only dual responders developed AHR (PC150 decreased, P less than 0.05). There were no significant differences in BAL between the two groups. Six dual responders were then, on separate occasions (greater than or equal to 3 wk), pretreated with placebo, indomethacin (2 mg/kg iv), or a leukotriene antagonist, FPL-57231 (30 mg inhaled). Neither agent significantly affected the acute response to antigen. Only FPL pretreatment blocked the late response, but both agents blocked the antigen-induced AHR 24 h later. BAL at 24 h showed no significant differences. These results indicate that only dual responders develop AHR 24 h after antigen challenge. This AHR appears independent of the late increase in sRL or the severity of pulmonary inflammation. AHR appears to be sensitive to agents that interfere with the early release or actions of cyclooxygenase and lipoxygenase metabolites in dual responders.     

Increased in vitro airway responsiveness in sheep following repeated exposure to antigen in vivo

We have studied the effect of repeated in vivo antigen exposure on in vitro airway responsiveness in sensitized sheep. Fourteen sheep underwent five biweekly exposures to aerosolized Ascaris suum antigen or saline. Following this exposure regimen, the animals were killed and tracheal smooth muscle and lung parenchymal strips were prepared for in vitro studies of isometric contraction in response to histamine, methacholine, prostaglandin F2 alpha, and a thromboxane A2 analogue. No alteration in tracheal smooth muscle responsiveness was observed between saline- and antigen-exposed tissue. In contrast, by use of lung parenchymal strips as an index of peripheral airway responsiveness, significant increases in responsiveness to histamine and a thromboxane A2 analogue (10(-6) and 10(-5) M) were observed in antigen-exposed tissue compared with saline controls. These results demonstrate that repeated antigen exposure in vivo selectively increase the responsiveness of peripheral lung smooth muscle to certain chemical mediators of anaphylaxis.     

The inhaled Rho kinase inhibitor Y-27632 protects against allergen-induced acute bronchoconstriction, airway hyperresponsiveness, and inflammation

Recently, we have shown that allergen-induced airway hyperresponsiveness (AHR) after the early (EAR) and late (LAR) asthmatic reaction in guinea pigs could be reversed acutely by inhalation of the Rho kinase inhibitor Y-27632. The present study addresses the effects of pretreatment with inhaled Y-27632 on the severity of the allergen-induced EAR and LAR, the development of AHR after these reactions, and airway inflammation. Using permanently instrumented and unrestrained ovalbumin (OA)-sensitized guinea pigs, single OA challenge-induced EAR and LAR, expressed as area under the lung function (pleural pressure, P(pl)) time-response curve, were measured, and histamine PC(100) (provocation concentration causing a 100% increase of P(pl)) values were assessed 24 h before, and at 6 and 24 h after, the OA challenge (after the EAR and LAR, respectively). Thirty minutes before and 8 h after OA challenge, saline or Y-27632 (5 mM) was nebulized. After the last PC(100) value, bronchoalveolar lavage (BAL) was performed, and the inflammatory cell profile was determined. It was demonstrated that inhalation of Y-27632 before allergen challenge markedly reduced the immediate allergen-induced peak rise in P(pl), without significantly reducing the overall EAR and LAR. Also, pretreatment with Y-27632 considerably protected against the development of AHR after the EAR and fully prevented AHR after the LAR. These effects could not be explained by a direct effect of Y-27632 on the histamine responsiveness, because of the short duration of the acute bronchoprotection of Y-27632 (<90 min). In addition, Y-27632 reduced the number of total inflammatory cells, eosinophils, macrophages, and neutrophils recovered from the BAL. Altogether, inhaled Y-27632 protects against acute allergen-induced bronchoconstriction, development of AHR after the EAR and LAR, and airway inflammation in an established guinea pig model of allergic asthma.     

Inhalation of sphingosine kinase inhibitor attenuates airway inflammation in asthmatic mouse model

Sphingosine 1-phosphate (S1P) produced by sphingosine kinase (SPHK) is implicated in acute immunoresponses, however, mechanisms of SPHK/S1P signaling in the pathogenesis of bronchial asthma are poorly understood. In this study, we hypothesized that SPHK inhibition could ameliorate lung inflammation in ovalbumin (OVA)-challenged mouse lungs. Six- to eight-week-old C57BL/6J mice were sensitized and exposed to OVA for 3 consecutive days. Twenty-four hours later, mice lungs and bronchoalveolar lavage (BAL) fluid were analyzed. For an inhibitory effect, either of the two different SPHK inhibitors, N,N-dimethylsphingosine (DMS) or SPHK inhibitor [SK-I; 2-(p-hydroxyanilino)-4-(p-chlorophenyl) thiazole], was nebulized for 30 min before OVA inhalation. OVA inhalation caused S1P release into BAL fluid and high expression of SPHK1 around bronchial epithelial walls and inflammatory areas. DMS or SK-I inhalation resulted in a decrease in S1P amounts in BAL fluid to basal levels, accompanied by decreased eosinophil infiltration and peroxidase activity. The extent of inhibition caused by DMS inhalation was higher than that caused by SK-I. Like T helper 2 (Th2) cytokine release, OVA inhalation-induced increase in eotaxin expression was significantly suppressed by DMS pretreatment both at protein level in BAL fluid and at mRNA level in lung homogenates. Moreover, bronchial hyperresponsiveness to inhaled methacholine and goblet cell hyperplasia were improved by SPHK inhibitors. These data suggest that the inhibition of SPHK affected acute eosinophilic inflammation induced in antigen-challenged mouse model and that targeting SPHK may provide a novel therapeutic tool to treat bronchial asthma.     

Atropine pretreatment enhances airway hyperreactivity in antigen-challenged guinea pigs through an eosinophil-dependent mechanism

Airway hyperreactivity in antigen-challenged animals is mediated by eosinophil major basic protein (MBP) that blocks inhibitory M(2) muscarinic receptors on parasympathetic nerves, increasing acetylcholine release onto M(3) muscarinic receptors on airway smooth muscle. Acutely, anticholinergics block hyperreactivity in antigen-challenged animals and reverse asthma exacerbations in the human, but are less effective in chronic asthma. We tested whether atropine, given before antigen challenge, affected hyperreactivity, M(2) receptor function, eosinophil accumulation, and activation. Sensitized guinea pigs received atropine (1 mg/kg ip) 1 h before challenge and 6 h later. Twenty-four hours after challenge, animals were anesthetized, vagotomized, paralyzed, and ventilated. Airway reactivity to electrical stimulation of the vagi and to intravenous acetylcholine was not altered by atropine pretreatment in nonsensitized animals, indicating that atropine was no longer blocking postjunctional muscarinic receptors. Antigen challenge induced airway hyperreactivity to vagal stimulation that was significantly potentiated by atropine pretreatment. Bronchoconstriction induced by acetylcholine was not changed by antigen challenge or by atropine pretreatment. M(2) receptor function was lost in challenged animals but protected by atropine pretreatment. Eosinophils in bronchoalveolar lavage and within airway tissues were significantly increased by challenge but significantly reduced by atropine pretreatment. However, extracellular MBP in challenged airways was significantly increased by atropine pretreatment, which may account for reduced eosinophils. Depleting eosinophils with antibody to IL-5 before challenge prevented hyperreactivity and significantly reduced MBP in airways of atropine-pretreated animals. Thus atropine pretreatment potentiated airway hyperreactivity by increasing eosinophil activation and degranulation. These data suggest that anticholinergics enhance eosinophil interactions with airway nerves.     

Tachyphylaxis to inhaled methacholine in normal but not asthmatic subjects

Methacholine inhalation tests measure airway responsiveness in asthmatic and normal subjects. Tachyphylaxis occurs with repeated methacholine inhalations in normal subjects. The purpose of this study was to examine the time course and mechanisms of methacholine tachyphylaxis in normal subjects and to determine whether this occurs in mildly asthmatic subjects. Fifteen normal and nine asthmatic subjects were studied on 2 study days, at least 48 h apart. Each day, two inhalation tests were carried out. On one day, subjects performed two methacholine inhalation tests 3 h later by a methacholine test. Results were expressed as the provocation concentration causing a 20% fall in forced expiratory volume in 1 s (FEV1), (PC20). All normal subjects developed methacholine tachyphylaxis. The mean PC20 increased from 47.3 mg/ml (%SE 1.34) to 115.6 (%SE 1.51) (P less than 0.0001) in a 3-h interval. This increase lasted for greater than or equal to 6 h (P = 0.012). Asthmatic subjects did not develop methacholine tachyphylaxis. Their mean methacholine PC20s were 1.6 mg/ml (%SE 1.4) and 1.5 (%SE 1.4) (P = 0.75) 3 h later. In two other series of experiments, normal subjects were pretreated with the cyclooxygenase inhibitors indomethacin (100 mg/day) or flurbiprofen (150 mg/day) or a placebo for 3 days before two methacholine tests 3 h apart. Both indomethacin and flurbiprofen significantly inhibited the development of methacholine tachyphylaxis. These results confirm that methacholine tachyphylaxis occurs in normal subjects, lasts greater than or equal to 6 h, and may occur through the release of inhibitory prostaglandins. By contrast, methacholine tachyphylaxis does not occur in asthmatic subjects.     

Ozone increases susceptibility to antigen inhalation in allergic dogs

To determine whether O3 exposure increased airway responsiveness to antigen inhalation, we studied airway responsiveness to acetylcholine (ACh) and Ascaris suum antigen (AA) before and after O3 in dogs both sensitive and insensitive to AA. Airway responsiveness was assessed by determining the provocative concentration of ACh and AA aerosols that increased respiratory resistance (Rrs) to twice the base-line value. O3 (3 parts per million) increased airway responsiveness to ACh in dogs both sensitive and insensitive to AA, and it significantly decreased the ACh provocation concentration from 0.541 +/- 0.095 to 0.102 +/- 0.047 (SE) mg/ml (P less than 0.01; n = 10). AA aerosols, even at the highest concentration in combination with O3, did not increase Rrs in dogs insensitive to AA. However, O3 increased airway responsiveness to AA in AA-sensitive dogs and significantly decreased log AA provocation concentration from 2.34 +/- 0.22 to 0.50 +/- 0.17 (SE) log protein nitrogen units/ml (P less than 0.01; n = 7). O3-induced hyperresponsiveness to ACh returned to the base-line level within 2 wk, but hyperresponsiveness to AA continued for greater than 2 wk. The plasma histamine concentration after AA challenge was significantly higher after than before O3 (P less than 0.01). Intravenous infusion of OKY-046 (100 micrograms.kg-1.min-1), an inhibitor of thromboxane synthesis, inhibited the O3-induced increase in responsiveness to ACh, but it had no effects on the O3-induced increase in responsiveness to AA and the increase in the plasma histamine concentration. These results suggest that O3 increases susceptibility to the antigen in sensitized dogs via a different mechanism from that of O3-induced muscarinic hyperresponsiveness.     

Nedocromil sodium in allergen-induced bronchial responses and airway hyperresponsiveness in allergic sheep

We examined the effects of nedocromil sodium, a new drug developed for the treatment of reversible obstructive airway disease, on allergen-induced early and late bronchial responses and the development of airway hyperresponsiveness 24 h after challenge in nine allergic sheep. On occasions greater than 2 wk apart the sheep were treated with 1) placebo aerosol (buffered saline) before and 3 h after antigen challenge, 2) an aerosol of nedocromil sodium (1 mg/kg in 3 ml buffered saline) before antigen challenge and placebo 3 h after challenge, and 3) placebo aerosol before and nedocromil sodium aerosol 3 h after challenge. Early and late bronchial responses were determined by measuring specific lung resistance (sRL) before and periodically after challenge. Airway responsiveness was assessed by determining from dose-response curves the carbachol concentration (in % wt/vol) that increased sRL to 5 cmH2O/s. In the placebo trial, antigen challenge resulted in early and late increases in sRL over a base line of 353 +/- 32 and 131 +/- 17% (SE), respectively. Both early and late increases in sRL were blocked (P less than 0.05) when the sheep were pretreated with nedocromil sodium. When nedocromil was given after the early response, the late response was reduced significantly. Eight of nine sheep developed airway hyperresponsiveness 24 h after antigen challenge. In these eight sheep, carbachol concentration before antigen challenge was 2.6 +/- 0.3%, 24 h later carbachol concentration was significantly lower (1.8 +/- 0.3%). Both nedocromil sodium treatments blocked (P less than 0.05) this antigen-induced airway hyperresponsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)     

O3-induced airway hyperresponsiveness to noncholinergic system and other stimuli.

The effect of O3 exposure (3 ppm, 1 h) on the in vivo and in vitro airway responsiveness, as well as the changes in cell contents in bronchoalveolar lavage (BAL) fluid, were evaluated 16-18 h after O3 exposure in sensitized and nonsensitized male guinea pigs. The sensitization procedure was performed through repeated inhalation of ovalbumin for 3 wk. Increase in pulmonary insufflation pressure produced by the excitatory nonadrenergic noncholinergic (eNANC) system, histamine, and antigen were assessed in in vivo conditions, whereas airway responsiveness to histamine and substance P was evaluated in in vitro conditions by use of tracheal chains with or without epithelium and lung parenchymal strips. We found that O3 exposure 1) increased the neutrophil content in BAL fluids in both sensitized and nonsensitized guinea pigs, 2) caused hyperresponsiveness to eNANC stimulation in nonsensitized guinea pigs (although combination of sensitization and O3 exposure paradoxically abolished the hyperresponsiveness to eNANC stimulation), 3) increased the in vivo bronchoconstrictor responses to histamine and antigen, 4) caused hyperresponsiveness to substance P in nonsensitized tracheae with or without epithelium and in sensitized tracheae with epithelium, 5) did not modify the responsiveness to histamine in tracheae with or without epithelium (and in addition, epithelium removal caused hyperresponsiveness to histamine even in those tracheae exposed to O3), and 6) produced hyperresponsiveness to histamine in lung parenchymal strips either from sensitized or nonsensitized guinea pigs.