The Basenji-Greyhound dog model of asthma: leukocyte histamine release, serum IgE, and airway response to inhaled antigen

To understand the immunologic mechanisms underlying the variation in airway response to inhaled Ascaris antigen (AA) in Basenji-Greyhound (BG) dogs having hyperreactive airways, we examined the relationship between leukocyte histamine release, Ascaris-specific serum IgE, changes in pulmonary resistance (RL), and decreases in dynamic compliance (Cdyn). All Ascaris-sensitive BG dogs showing airway responses to AA aerosol challenge exhibited an antigen dose-dependent release of leukocyte histamine, with total leukocyte histamine ranging from 68 to 123 ng/10(7) cells. Airway response to inhaled antigen more closely correlated with antigen dose releasing 50% total leukocyte histamine (RL, r = 0.94); Cdyn, r = 0.82), than with circulating levels of antigen-specific IgE (RL, r = 0.68; Cdyn, r = 0.69). We conclude that the airway response of sensitized BG dogs to AA inhalations is more dependent on factors affecting mediator release from pulmonary sources than circulating specific reaginic antibody.     

Antigen sensitization and methacholine responses in dogs with hyperreactive airways

Antigen sensitization was induced in six Basenji-Greyhound (BG) dogs by weekly aerosol exposure to Ascaris suum. The effects on airway responsiveness to inhaled methacholine were studied before and at least 2 wk following Ascaris sensitization. All dogs developed detectable serum levels of Ascaris-specific immunoglobulin E (IgE), and five out of six dogs developed airway responsiveness to antigen over the 4- to 6-mo period. This was accompanied by a decrease rather than an increase in airway responsiveness to inhaled methacholine. When dogs were challenged with methacholine 30 min after Ascaris antigen aerosol challenge, however, dogs reactive to Ascaris became hyperresponsive to methacholine. The magnitude of the response to antigen correlated (r = 0.85) inversely with the dose of methacholine increasing pulmonary resistance 200%. These data show that in BG dogs airway responsiveness to methacholine is increased by acute antigen exposure but that sensitization of previously unsensitized dogs does not increase nonspecific airway responsiveness.     

Immunologic mast cell-mediated responses and histamine release are attenuated by heparin.

Heparin has been shown to act as a competitive inhibitor of inositol 1,4,5-triphosphate (InsP3) receptors in various cell types. Because InsP3 is one of the second messengers involved in stimulus-secretion coupling in mast cells, it is possible that heparin may inhibit mast cell-mediated reactions. Therefore, in allergic sheep, we tested this hypothesis in two mast cell-mediated reactions induced by immunologic and nonimmunologic stimuli: immediate cutaneous reaction (ICR) and acute bronchoconstrictor response (ABR). In 12 sheep allergic to Ascaris suum antigen, the surface area of the skin wheal was determined 20 min after intradermal injection (0.05 ml) of increasing concentrations of specific antigen, compound 48/80, and histamine, without and after pretreatment with heparin (100, 300, or 1,000 U/kg i.v.). Antigen, compound 48/80, and histamine produced concentration-dependent increases in ICR. Heparin "partially" inhibited the ICR to antigen and compound 48/80 in a dose-dependent manner without modifying the ICR to histamine. The heparin preservative benzyl alcohol was ineffective. In 11 additional sheep, specific lung resistance was measured before and after inhalation challenges with antigen, compound 48/80, and histamine without and with aerosol heparin pretreatment (1,000 U/kg). Heparin blocked the antigen- and compound 48/80-induced bronchoconstriction without modifying the airway effects of histamine. In isolated human uterine mast cells, heparin inhibited the anti-immunoglobulin E- but not the calcium ionophore- (A23187) induced histamine release. These data suggest that heparin inhibits the ICR and ABR induced by stimuli that produce immunologic and nonimmunologic mast cell degranulation without attenuating the effects of histamine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Airway responses to inhaled ouabain and histamine in conscious guinea pigs

Tracheal Na+-K+-ATPase activity is positively correlated with in vivo airway responsiveness to histamine. We wondered whether this were a chance association or whether it was directly related to the mechanism of hyperreactivity. Therefore, we obtained dose-response curves to aerosols of histamine and ouabain in guinea pigs to determine whether an in vivo relationship existed between the excitatory effects of histamine and the enzyme-inhibiting effect of ouabain. Airway responsiveness to ouabain was measured as the ouabain concentration producing a 30% decrease in specific airway conductance (ED30) or that producing a half-maximal response (ED50). Responsiveness to histamine was measured either as ED30 or as ED50. Significant positive correlations were noted between the log ED50 of ouabain and log histamine ED30 or ED50 (r = 0.81 and 0.83, respectively; P less than 0.001), and between log ouabain ED30 and log histamine ED30 and ED50 (r = 0.76 and 0.77, respectively; P less than 0.002). Pretreatment with ouabain increased airway responsiveness to histamine (P less than 0.05). We suggest that in hyperreactive airways Na+-K+-ATPase serves a homeostatic function of preventing Na+ and Ca2+ loading of the cell and that it is not directly responsible for the hyperreactivity.     

Effects of granulocyte depletion on pulmonary responsiveness to aerosol histamine

The effects of granulocyte depletion with hydroxyurea on pulmonary responsiveness to aerosol histamine were studied in 10 chronically instrumented unanesthetized sheep. Sheep were studied when granulocyte counts were normal (B), after 3 days of hydroxyurea but before granulocyte counts had dropped below 700 cells/mm3 (H), and after granulocyte counts had fallen below 200 cells/mm3 (D). Hydroxyurea itself had no effect on aerosol histamine responsiveness and the results were unaffected by the order of experimentation. All 10 sheep were less responsive (P less than 0.05) to aerosol histamine when granulocyte depleted effective dose of histamine that caused a reduction to 65% of control dynamic compliance (ED65Cdyn = 23.98 +/- 4.70 mg/ml) compared with base line (ED65Cdyn = 7.06 +/- 1.86 mg/ml). Those sheep initially most responsive to aerosol histamine had the greatest attenuation in their airway responsiveness to aerosol histamine (P less than 0.05). There was a significant negative correlation between absolute granulocyte counts in peripheral blood and pulmonary responsiveness to aerosol histamine during base-line (B) condition (r = -0.74, P less than 0.05) and for the data as a whole [r = -0.69, P less than 0.05 (B + H + D)]. Circulating granulocytes and/or pulmonary inflammation may contribute to pulmonary responsiveness to bronchial 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.     

Potentiation of histamine release by sodium cromoglycate.

Human lung slices passively sensitized with allergic serum released histamine when incubated with specific antigen and anti-IgE but anti-IgG had no effect. Sodium cromoglycate (SCG) inhibited antigen induced histamine release but the dose-response curve was bell-shaped. Inhibition of anti-IgE induced release was linearly related to dose, whereas that induced by anti-IgG was potentiated by increasing doses of SCG. After sensitization with allergic serum in which IgE had been inactivated by heating, specific antigen released little or no histamine but this was potentiated by SCG. It is concluded that SCG inhibits IgE mediated but potentiates IgG mediated allregic reactions thus explaining its characteristic dose-response curve $\text{in vitro}$.     

Release of epithelium-derived relaxing factor after ozone inhalation in dogs

Airway epithelium has been reported to release epithelium-derived relaxing factor (EpDRF), which inhibits contraction of airway smooth muscle. This study tested the hypothesis that airway hyperresponsiveness after inhalation of ozone in dogs results from an inability to produce EpDRF. Two groups of five dogs each were studied; one group inhaled ozone, the other dry room air. Ozone-treated dogs developed airway hyperresponsiveness, whereas the control group did not. The acetylcholine provocative concentration decreased from 4.17 (%SE 1.35) to 0.56 mg/ml (%SE 1.24) (P = 0.0006) in the ozone-treated dogs and was 18.76 (%SE 2.04) and 29.77 mg/ml (%SE 2.07) in the air-treated dogs (P = 0.47). In vitro the presence of airway epithelium reduced the constrictor responses to acetylcholine, histamine, serotonin, and KCl in trachealis strips from the control dogs. This effect of epithelium was still present in trachealis strips from dogs with airway hyperresponsiveness. These results demonstrate that EpDRF is released from canine tracheal epithelium, that this function is not impaired in dogs with airway hyperresponsiveness after inhaled ozone, and that loss of EpDRF is not responsible for the development of airway hyperresponsiveness after inhaled ozone in dogs.     

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.     

Late phase bronchial obstruction following nonimmunologic mast cell degranulation

Immunologic degranulation of airway mast cells after antigen inhalation produces early and late airway obstructions in allergic sheep. In this study we determined whether nonimmunologic degranulation of airway mast cells by inhalation of compound 48/80 had similar effects. In five sheep, pulmonary flow resistance (RL), thoracic gas volume (Vtg), and arterial O2 tension (Pao2) were determined prior to and at predetermined times after inhalation of 48/80 aerosol. Immediately after challenge mean specific lung resistance (sRL = RL X Vtg) increased by 259% and mean Pao2 decreased by 29%. All values returned to normal by 3 h. By 5-h postchallenge sRL again increased significantly; this second increase in sRL (92% above base line) was maximal at 7 h and was accompanied by a 17% drop in Pao2. In these same sheep inhalation of Ascaris suum antigen produced comparable early changes in sRL, but the onset of the late response was somewhat delayed and more pronounced. In a second group of sheep (n = 5), pretreatment with the mast cell stabilizer cromolyn sodium prevented both early and late responses by compound 48/80. Pretreatment with the histamine H1-antagonist chlorpheniramine had no significant effect on either response, whereas pretreatment with FPL 55712, an antagonist of slow-reacting substance of anaphylaxis (SRS-A), slightly but not significantly attenuated the early response and completely prevented the late response. We conclude that, like immunologic stimuli, nonimmunologic mast cell degranulation produces early and late bronchial obstructions in allergic sheep; that these responses are mediator dependent; and that while histamine and SRS-A contribute to the early response, it is the early appearance of SRS-A which is an important prerequisite for the late response.     

Airway hyperresponsiveness to bronchoconstrictor challenge after wood smoke exposure in guinea pigs.

Prior airway exposure to wood smoke induces an increase in airway responsiveness to subsequent smoke inhalation in guinea pigs (Life Sci. 63: 1513, 1998; 66: 971, 2000). To further characterize this airway hyperreactivity, we investigated and compared the airway responsiveness to bronchoconstrictor challenge before and 30 min after sham air exposure or wood smoke exposure in anesthetized and artificially ventilated guinea pigs. Various doses of substance P (0.8-6.4 microg/kg), capsaicin (0.2-3.2 microg/kg), prostaglandin F2alpha (30-3000 microg/kg), histamine (1-8 microg/kg), or acetylcholine (5-20 microg/kg) were intravenously injected at 2-min intervals in successively increasing doses to obtain the dose required to provoke a 200% increase in baseline total lung resistance (ED200). Wood smoke exposure significantly lowered the ED200 of substance P, capsaicin, and prostaglandin F2alpha whereas sham air exposure failed to do so. Furthermore, wood smoke exposure did not significantly alter the ED200 of histamine or acetylcholine. Pretreatment with phosphoramidon (2 mg/kg), an inhibitor of the neutral endopeptidase (the major degradation enzyme of substance P), before smoke exposure did not significantly affect the smoke-induced reduction in ED200 of substance P. Sectioning both cervical vagi before smoke exposure did not significantly alter the smoke-induced reduction in ED200 of capsaicin or prostaglandin F2alpha. These results suggest that airway exposure to wood smoke acutely produces airway hyperresponsiveness to substance P, capsaicin, and prostaglandin F2alpha, but not to histamine or acetylcholine. Since the combination of phosphoramidon and wood smoke exposure did not result in an additive potentiation of smoke-induced airway hyperresponsiveness to substance P, it is suggested that an inhibition of the degradation enzyme of substance P may contribute to this increase in airway reactivity. Furthermore, vagally-mediated bronchoconstriction does not play a vital role in enhanced airway responsiveness to capsaicin or prostaglandin F2alpha.     

Evidence for platelet-activating factor secretion during immune activation in dogs

To elucidate the potential physiological significance of platelet-activating factor (PAF) in acute bronchoconstriction, we studied the effect of Ascaris suum antigen on the tachyphylactic response to PAF in 15 natively allergic mongrel dogs in vivo. Active bronchial tension was measured isometrically, and mediator secretion was measured as the arteriovenous difference (AVd) in plasma concentration across the lungs. Administration of PAF into the bronchial artery caused dose-related contraction in five control dogs (maximal active tension = 11.8 +/- 1.68 g/cm) that paralleled the increase in the AVd for serotonin (4,188 +/- 175 pg/ml) but not histamine (maximal AVd less than 6.0 ng/ml). The response to PAF was highly tachyphylactic. In contrast to PAF, 1:10 concentration of intra-arterial antigen caused substantial release of histamine (AVd = 308 +/- 57.1 ng/ml; P less than 0.001 vs. PAF). Diminished responsiveness (2-log shift in threshold and maximal contraction; P less than 0.001) to PAF was demonstrated in five dogs after 1:10 antigen, compatible with endogenous release of PAF during prior immune challenge in the same animals. Administration of Ascaris antigen caused a leftward shift in the dose-response curve to serotonin and only mild tachyphylaxis to the maximal response to histamine. Our data are compatible with physiological participation of PAF in eliciting bronchial smooth muscle contraction during the acute phase of immune activation caused by A. suum antigen.     

Inhibition of allergic late airway responses by inhaled heparin-derived oligosaccharides.

Inhaled heparin has been shown to inhibit allergic bronchoconstriction in sheep that develop only acute responses to antigen (acute responders) but was ineffective in sheep that develop both acute and late airway responses (LAR) (dual responders). Because the antiallergic activity of heparin is molecular-weight dependent, we hypothesized that heparin-derived oligosaccharides (<2, 500) with potential anti-inflammatory activity may attenuate the LAR in the dual-responder sheep. Specific lung resistance was measured in 24 dual-responder sheep before and serially for 8 h after challenge with Ascaris suum antigen for demonstration of early airway response (EAR) and LAR, without and after treatment with inhaled medium-, low-, and ultralow-molecular-weight (ULMW) heparins and "non-anticoagulant" fractions (NAF) of heparin. Airway responsiveness was estimated before and 24 h postantigen as the cumulative provocating dose of carbachol that increased specific lung resistance by 400%. Only ULMW heparins caused a dose-dependent inhibition of antigen-induced EAR and LAR and postantigen airway hyperresponsiveness (AHR), whereas low- and medium-molecular-weight heparins were ineffective. The effects of ULMW heparin and ULMW NAF-heparin were comparable and inhibited the LAR and AHR even when administered "after" the antigen challenge. The ULMW NAF-heparin failed to inhibit the bronchoconstrictor response to histamine, carbachol, and leukotriene D(4), excluding a direct effect on airway smooth muscle. In six sheep, segmental antigen challenge caused a marked increase in bronchoalveolar lavage histamine, which was not prevented by inhaled ULMW NAF-heparin. The results of this study in the dual-responder sheep demonstrate that 1) the antiallergic activity of inhaled "fractionated" heparins is molecular-weight dependent, 2) only ULMW heparins inhibit the antigen-induced EAR and LAR and postantigen AHR, and 3) the antiallergic activity is mediated by nonanticoagulant fractions and resides in the ULMW chains of <2,500.     

Mast cell heterogeneity in higher animals: a comparison of the properties of autologous lung and intestinal mast cells from nonhuman primates

The issue of mast cell heterogeneity has been investigated in nonhuman primates by a comparative examination of lung and intestinal mast cells. These cells were obtained in parallel from the respective tissues of individual monkeys by an identical enzymatic dispersion technique. Mast cells derived from the lungs differed from those derived from the intestine in that the majority of the former cell type could be stained with toluidine blue at pH 4 to 5, whereas the intestinal mast cells in the dispersed preparations required a more acidic pH (less than 1) to display metachromasia. In addition, the lung cells exhibited an increased content of the mast cell mediator histamine. Nonhuman primate lung mast cells were also quantitatively more responsive to an immunologic challenge than their intestinal counterparts in that they released a higher percentage of cellular histamine and generated more leukotriene C4 on stimulation. Considerable inter-animal variation was observed between the magnitude of mediator release from both mast cell types after anaphylactic activation, but evidence for the presence in nonhuman primates of the phenomenon of releasability was not obtained. The responsiveness of both cell types to a range of potential nonimmunologic secretagogues and anti-allergic agents, including compound 48/80, substance P, theophylline, and isoprenaline, was essentially similar. We conclude that mast cell heterogeneity in higher animals may be reflected more by cytochemical rather than by functional differences between mast cell classes.     

Effect of age on lung mechanics and airway reactivity in lambs

We studied airway reactivity (AR) to aerosolized histamine, carbachol, and citric acid in lambs 1 mo of age to adulthood. Awake lambs were intubated and studied in a plethysmograph that measured dynamic compliance (Cdyn), resistance of the lung (RL), and functional residual capacity (FRC). Pleural pressure was measured using a Silastic balloon in the pleural space, and airway opening pressure (Pao) was measured using a catheter placed 1-2 cm distal to the nasotracheal tube. At the ages of 1, 3, 5, and 7 mo and adulthood, measurements of Cdyn, RL, and FRC were obtained in 46 sheep (22 males, 24 females). AR to carbachol, histamine, and citric acid was measured in each sheep in randomized order on three separate days by giving increasing concentrations of the drug in a noncumulative fashion. The dose that would have caused a 35% reduction in Cdyn (ED65Cdyn), a doubling of RL (ED200RL), or a 50% increase in FRC (ED150FRC) was calculated. In both males and females, base-line Cdyn increased (r = 0.81, P less than 0.01) with age, as did FRC (r = 0.87, P less than 0.01). There was no significant change in RL in either sex with age or in the group as a whole. There was a significant increase in AR to both histamine and carbachol with increasing age as measured by a decrease in ED65Cdyn (P less than 0.01 and P less than 0.05, respectively) with age. There was no significant change in AR with age as measured by RL or FRC for any of the three bronchoconstrictors tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological characterization of airway smooth muscle responses to antigen in ascaris-sensitive dogs

The dog model of ascaris airway sensitivity was chosen because of its frequency and its immunologic similarity to the human atopic asthmatic state. We studied the mediators of the antigen-induced airway response in vitro and the alterations in the in vivo and in vitro responsiveness to spasmogens evoked by antigen challenge. A myogenic basis of altered reactivity was suggested by the following: tetrodotoxin-insensitive spontaneous active tone; phasic contractions of airway smooth muscle; and responsiveness to leukotrienes C4 and D4. The pharmacologic characteristics of the antigen-induced airway smooth muscle contraction in vitro were similar to those induced by arachidonic acid and the leukotrienes only in some respects but were clearly different from those induced by compound 48/80. This suggested a predominant role for arachidonate lipoxygenase products. Histamine appeared to play a minor role in the antigen response. Comparisons were made between antigen-induced responses of actively and passively sensitized airways tissues. In the latter, histamine release appeared to contribute to the initial antigen-induced contraction and, unlike in actively sensitized airways, the responses were easily desensitized to repeated challenge. Alterations of airway responsiveness were demonstrated in vivo to acetylcholine and 5-HT following antigen challenge of highly ascaris-sensitive dogs. In vitro studies of passively sensitized muscle showed selectively enhanced response to 5-HT following antigen challenge. These studies support the presence of altered myogenic properties of airway smooth muscle and nonspecific increased airway responsiveness in this animal model.     

Repeated antigen inhalation results in a prolonged airway eosinophilia and airway hyperresponsiveness in primates

The effects of repeated antigen inhalation on airway cellular composition and airway responsiveness were examined in primates. Airway cellular composition was assessed by bronchoalveolar lavage (BAL), and airway responsiveness was measured as the bronchoconstrictor response to cumulative methacholine dose-response determinations over the course of a 10-wk study. Control animals, exposed to repeated vehicle inhalation challenges, were tested in parallel with the antigen-challenged group. Repeated antigen inhalation resulted in a prolonged inflammatory reaction characterized by a large increase in airway eosinophils (3 +/- 1 to 59 +/- 15%, P less than 0.01). Airway eosinophilia was associated with an increase in airway responsiveness as indicated by a leftward shift in the methacholine dose-response curves, an increase in the slope of the dose-response curves, and a decrease in PC100 values (the dose of methacholine required to cause a 100% increase in lung resistance). The number of BAL eosinophils and the level of eosinophil major basic protein in BAL correlated significantly with methacholine PC100 values (r = 0.61, P less than 0.01 and r = 0.64, P less than 0.01, respectively). Histological examination of lung biopsy samples taken at week 10 of the study demonstrated a striking infiltration of eosinophils in the antigen-challenged animals. These results support earlier observations that demonstrated an association between increases in airway eosinophils and increases in airway responsiveness and suggest that eosinophils are involved in the pathogenesis of hyperresponsive airways.     

Tachyphylaxis to inhaled aerosolized histamine in anesthetized dogs

Three consecutive dose-response curves to inhaled aerosolized histamine, separated by 1-h intervals, were obtained in 20 anesthetized mongrel dogs. In general, successive histamine dose-response curves shifted progressively rightward. Changes in pulmonary resistance (RL) and dynamic compliance (Cdyn) in response to low concentrations of histamine were reproducible, but responses to high concentrations (sufficient to at least double RL or decrease Cdyn by at least 30%) decreased on successive dose-response curves. The concentration of histamine required to double RL increased significantly (P less than 0.05) from 1.01 mg/ml on the first to 1.62 and 2.02 mg/ml on the second and third dose-response curves. In contrast, consecutive methacholine dose-response curves were not significantly different. Indomethacin pretreatment (5 mg/kg iv) prevented histamine tachyphylaxis, whereas atropine (4 mg iv) did not. However, indomethacin did not alter base-line pulmonary mechanics or histamine responsiveness as measured on the first dose-response curve. We conclude that tachyphylaxis to inhaled aerosolized histamine occurs in anesthetized dogs. Our results are consistent with an important role for endogenous prostaglandins in modulating the airway responses to repeated histamine exposures.     

Airway smooth muscle responsiveness from dogs with airway hyperresponsiveness after O3 inhalation

Airway hyperresponsiveness occurs after inhalation of O3 in dogs. The purpose of this study was to examine the responsiveness of trachealis smooth muscle in vitro to electrical field stimulation, exogenous acetylcholine, and potassium chloride from dogs with airway hyperresponsiveness after inhaled O3 in vivo and to compare this with the responsiveness of trachealis muscle from control dogs. In addition, excitatory junction potentials were measured with the use of single and double sucrose gap techniques in both groups of dogs to determine whether inhaled O3 affects the release of acetylcholine from parasympathetic nerves in trachealis muscle. Airway hyperresponsiveness developed in all dogs after inhaled O3 (3 ppm for 30 min). The acetylcholine provocative concentration decreased from 4.11 mg/ml before O3 inhalation to 0.66 mg/ml after O3 (P less than 0.0001). The acetylcholine provocative concentration increased slightly after control inhalation of dry room air. Airway smooth muscle showed increased responses to both electrical field stimulation and exogenous acetylcholine but not to potassium chloride in preparations from dogs with airway hyperresponsiveness in vivo. The increased response to electrical field stimulation was not associated with a change in excitatory junctional potentials. These results suggest that a postjunctional alteration in trachealis muscle function occurs after inhaled O3 in dogs, which may account for airway hyperresponsiveness after O3 in vivo.     

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.