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.     

Methylprednisolone restores sensitivity to beta-adrenergic agonists in Basenji-Greyhound dogs.

This study investigated the effect of chronic methylprednisolone treatment on the ability of albuterol and aminophylline to inhibit methacholine-induced airway constriction in Basenji-Greyhound (BG) dogs in vivo. Pulmonary responsiveness to methacholine was measured in five untreated BG dogs and in the same dogs pretreated with albuterol or aminophylline (which has been shown in this model to release endogenous catecholamines). Each dog was studied before, during, and after daily subcutaneous methylprednisolone for 6 wk. Changes in pulmonary resistance and dynamic compliance with methacholine aerosol challenge were measured. Neither baseline pulmonary function nor pulmonary responsiveness to aerosolized methacholine was significantly altered by albuterol, aminophylline, or chronic methylprednisolone administration alone. However, pretreatment with albuterol or aminophylline significantly attenuated airway responses to methacholine in BG dogs chronically receiving methylprednisolone. Because the reduced sensitivity to albuterol and aminophylline was restored by chronic methylprednisolone treatment, we conclude that at least part of the beneficial effects of corticosteroids on airways in BG dogs is through modulation of beta-adrenergic function.     

Airway responses in offspring of dogs with and without airway hyperreactivity

We examined airway responsiveness to aerosols of Ascaris suum, citric acid, and methacholine chloride in the offspring of two highly allergic breeds of dogs: Basenji-greyhounds (BG) and Basenjis (B). The BG parents had airway hyperresponsiveness to citric acid and methacholine, whereas the B parents did not. Both BG and B offspring were allergic as measured by many positive skin tests. BG offspring, like their parents, were hyperresponsive to citric acid and methacholine, whereas B offspring were not. We conclude that familial rather than environmental factors are important for the development of nonspecific airway hyperresponsiveness as well as allergy in the BG dog model of asthma. Allergic asthma in these animals represents a combination of two discrete processes: allergy and nonspecific airway hyperresponsiveness.     

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.     

O3-induced change in bronchial reactivity to methacholine and airway inflammation in humans

The increase in airway responsiveness induced by O3 exposure in dogs is associated with airway epithelial inflammation, as evidenced by an increase in the number of neutrophils (polymorphonuclear leukocytes) found in epithelial biopsies and in bronchoalveolar lavage fluid. We investigated in 10 healthy, human subjects whether O3-induced hyperresponsiveness was similarly associated with airway inflammation by examining changes in the types of cells recovered in bronchoalveolar lavage fluid obtained after exposure to air or to O3 (0.4 or 0.6 ppm). We also measured the concentrations of cyclooxygenase and lipoxygenase metabolites of arachidonic acid in lavage fluid. We measured airway responsiveness to inhaled methacholine aerosol before and after each exposure and performed bronchoalveolar lavage 3 h later. We found more neutrophils in the lavage fluid from O3-exposed subjects, especially in those in whom O3 exposure produced an increase in airway responsiveness. We also found significant increases in the concentrations of prostaglandins E2, F2 alpha, and thromboxane B2 in lavage fluid from O3-exposed subjects. These results show that in human subjects O3-induced hyperresponsiveness to methacholine is associated with an influx of neutrophils into the airways and with changes in the levels of some cyclooxygenase metabolites of arachidonic acid.     

Antigen challenge of sensitized rats increases airway responsiveness to methacholine

We measured airway responsiveness to methacholine (MCh) of highly inbred rats before and after six inhalational challenges with antigen. Ten Brown-Norway rats (130-216 g) that were actively sensitized to ovalbumin (OA) received six challenges with OA at 5-day intervals beginning 19 days after sensitization. An aerosol of OA (5% wt/vol) was inhaled for 1, 2, 5, and 10 min or until pulmonary resistance (RL) increased by at least 50%. Challenges with aerosolized MCh were performed immediately before and 14 days after sensitization, 2 days after the 3rd OA exposure, and 2, 7, 12, and 17 days after the 6th OA challenge. Four unsensitized rats underwent inhalational challenges with MCh over an equivalent time period. Responsiveness to MCh was calculated as the concentration of MCh required to increase RL to 200% of the control value (EC200RL). Seven out of 10 rats in the experimental group reacted to the first OA challenge with an immediate increase in RL of greater than 50% of control (range 70-550%). Three animals were unreactive to OA. Base-line EC200RL for all rats undergoing sensitization was 2.13 mg/ml (geometric mean), and it did not change significantly after sensitization (2.05 mg/ml). However, EC200RL of the rats that reacted to OA (n = 7) decreased significantly after 3 (1.11 mg/ml; P less than 0.005) and 6 OA exposures (0.96 mg/ml; P less than 0.005). The increase in responsiveness to inhaled MCh was present 17 days after the last OA exposure (EC200RL = 1.40 mg/ml; P less than 0.05). EC200RL of neither the unreactive sensitized rats (n = 3) nor the control rats (n = 4) changed after OA challenges.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

Mechanisms of airway hypercontractility in basenji-greyhound dogs

The comparative effects of contractile agonists and physiological stimulation of the tracheal and bronchial smooth muscle (BSM) response were studied isometrically in situ in five Basenji-greyhound (BG) and six mongrel dogs. Frequency-response curves generated by bilateral stimulation of the vagus nerves (0-20 Hz, 15-20 V, 2-ms duration) elicited greater maximal contraction in mongrel trachea (36.8 +/- 8.1 vs. 26.9 +/- 4.0 g/cm; P less than 0.02) and exhibited greater responsiveness in mongrel BSM (half-maximal response to electrical stimulation 3.0 +/- 1.1 vs. 7.0 +/- 0.5 Hz; P less than 0.05) compared with BG dogs. However, muscarinic sensitivity to intravenous methacholine (MCh) was substantially greater in BG dogs; MCh caused contraction greater than 1.5 g/cm at a mean dose of 3.0 X 10(-10) mol/kg for BG dogs compared with 5.1 X 10(-9) mol/kg for mongrel controls (P less than 0.03, Mann-Whitney rank-sum test). In contrast to the muscarinic response, the contractile response elicited by intravenous norepinephrine after beta-adrenergic blockade was similar in trachea and bronchus for both mongrel and BG dogs. Our data confirm previous in vitro demonstration of tracheal hyporesponsiveness in BG dogs and demonstrate that the contraction resulting from efferent parasympathetic stimulation is less in the BG than mongrel dogs. However, postsynaptic muscarinic responsiveness of BG BSM is substantially increased. We conclude that a component of airway responsiveness in BG dogs depends directly on contractile forces generated postsynaptically that are nongeometry dependent, postjunctional, and agonist specific.     

Calcium chelators increase airway responsiveness

To test the effect of calcium chelation on airway responsiveness to methacholine, purebred Basenji dogs were pretreated with a calcium-chelating aerosol (edetate disodium, Na2EDTA) or a placebo aerosol (saline or CaNa2-EDTA) and then challenged with methacholine bromide aerosols. The lowest dose of methacholine (0.15 mg/ml) produced no change in pulmonary resistance (RL) following pretreatment with the placebo aerosols, but RL increased (P less than 0.05) by 5.1 +/- 1.2 (SE) cmH2O X l-1 X s following pretreatment with Na2EDTA. The highest dose of methacholine (1.5 mg/ml) increased RL in all animals, but the increase was greater (P less than 0.01) following pretreatment with Na2EDTA (9.5 +/- 1.9 cm H2O X l-1 X s) than following pretreatment with a placebo aerosol (6.4 +/- 1.5 cmH2O X l-1 X s). These studies show that calcium-chelating aerosols significantly increase airway responsiveness and suggest that a localized calcium deficit may contribute to hyperresponsive airway disease.     

Effect of normobaric hyperoxia on airways of normal subjects

Airway responsiveness to inhaled cholinergic agonist during the early stage of pulmonary O2 toxicity was examined to determine whether normobaric hyperoxia alters airway function. Eight healthy nonsmoking males with moderate base-line methacholine responsiveness breathed normobaric O2 (greater than or equal to 95%) over 12 h and on another occasion breathed air in an identical protocol. Vital capacity, expiratory flow, airway responsiveness to methacholine, and respiratory symptoms were measured at 0, 4, 8, and 12 h while subjects breathed O2 and 12 h afterwards. After 12 h, forced vital capacity was significantly decreased with O2 breathing but not with air breathing. At 4, 8, or 12 h of exposure and 12 h after exposure, there was no difference in methacholine sensitivity or reactivity between O2 and air-exposure trials. The earliest manifestations of pulmonary normobaric O2 toxicity in normal adults include diminished vital capacity and the onset of respiratory symptoms, but early O2 toxicity does not produce altered responsiveness to inhaled methacholine.     

Reduced sensitivity to beta-adrenergic agonists in Basenji-Greyhound dogs

To investigate the inhibitory effects of beta-adrenergic agonists and aminophylline on pulmonary responsiveness, we evaluated the ability of albuterol and aminophylline to attenuate pulmonary responses to aerosol challenge with methacholine and histamine in intact Basenji-Greyhound (BG) and selected mongrel dogs. Pulmonary responses were measured in untreated dogs and in dogs pretreated with albuterol (1 and 2.5 micrograms/kg) or aminophylline. Before aerosol challenge, baseline pulmonary resistance (RL) and dynamic compliance (Cdyn) were not significantly different between the BGs and the mongrels. In the untreated dogs, pulmonary responses to methacholine and histamine aerosols were not different between the BGs and the mongrels. Pretreatment with albuterol (1 microgram/kg) or aminophylline significantly attenuated the pulmonary response to methacholine in the mongrels but was without effect in the BGs. Albuterol (2.5 micrograms/kg) significantly attenuated the pulmonary response to methacholine in the BGs and the mongrels; however, this attenuation was significantly greater (P less than 0.05) in the mongrels than in the BGs. In response to histamine challenge, no differences were seen between the BGs and the mongrels in the control state (no pretreatment) or after pretreatment with albuterol or aminophylline. This study demonstrates that in BGs pulmonary responsiveness to methacholine but not histamine is resistant to inhibition by beta-adrenergic agonists. This may result from a qualitative or quantitative defect in either the cholinergic or beta-adrenergic receptor or to an abnormality distal to the receptors in the signal transduction mechanism at a site where the two signals interact.     

Tidal midexpiratory flow as a measure of airway hyperresponsiveness in allergic mice

A method for the noninvasive measurement of airway responsiveness was validated in allergic BALB/c mice. With head-out body plethysmography and the decrease in tidal midexpiratory flow (EF(50)) as an indicator of airway obstruction, responses to inhaled methacholine (MCh) and the allergen ovalbumin were measured in conscious mice. Allergen-sensitized and -challenged mice developed airway hyperresponsiveness as measured by EF(50) to aerosolized MCh compared with that in control animals. This response was associated with increased allergen-specific IgE and IgG1 production, increased levels of interleukin-4 and interleukin-5 in bronchoalveolar lavage fluid and eosinophilic lung inflammation. Ovalbumin aerosol challenge elicited no acute bronchoconstriction but resulted in a significant decline in EF(50) baseline values 24 h after challenge in allergic mice. The decline in EF(50) to MCh challenge correlated closely with simultaneous decreases in pulmonary conductance and dynamic compliance. The decrease in EF(50) was partly inhibited by pretreatment with the inhaled beta(2)-agonist salbutamol. We conclude that measurement of EF(50) to inhaled bronchoconstrictors by head-out body plethysmography is a valid measure of airway hyperresponsiveness in mice.     

Inhaled Lead Exposure Affects Tracheal Responsiveness and Lung Inflammation in Guinea Pigs During Sensitization

Total and differential white blood cells (WBC), and cytokines, levels in serum were examined in guinea pigs exposed to inhaled lead acetate. Different groups of guinea pigs including: control (group C), sensitized group (group S), and exposed animals to aerosol of three lead concentrations during sensitization (n?=?6 for each group) were studied. Total and differential WBC counts of lung lavage, serum cytokine (IFNγ and IL-4), levels and tracheal responsiveness to methacholine and ovalbumin were measured. All measured values were significantly increased except for IFNγ/IL-4 ratio which was significantly decreased in nonexposed sensitized and those exposed to all lead concentrations compared to control group (p?<?0.05 to p?<?0.001). Most measured values in animals exposed to higher lead concentration were also significantly higher than group S except for tracheal responsiveness to methacholine and lymphocyte count. Lead concentration significantly increased in lung tissues of animals exposed to all three lead concentrations (p?<?0.001 for all cases). These results showed that lead exposure during sensitization can induce greater increase in tracheal responsiveness, total WBC, eosinophil, neutrophil, and basophil counts as well as serum level of IL-4. It can also cause a decrease in lymphocyte count, IFNγ level, and IFNγ/IL-4 ratio especially in its high concentration. Therefore inhaled lead exposure may cause increased severity of asthma during development of the disease.     

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.     

Transfer of the enhancing effect of respiratory syncytial virus infection on subsequent allergic airway sensitization by T lymphocytes.

In mice, respiratory syncytial virus (RSV) infection enhances allergic airway sensitization, resulting in lung eosinophilia and in airway hyperresponsiveness (AHR). The mechanisms by which RSV contributes to development of asthma and its effects on allergic airway sensitization in mice are not known. We tested whether these consequences of RSV infection can be adoptively transferred by T cells and whether depletion of T cell subsets prevents the effects of RSV infection on subsequent airway sensitization. Mononuclear cells, T lymphocytes, or CD4 or CD8 T cells from peribronchial lymph nodes (PBLN) of RSV-infected mice were transferred into naive BALB/c mice which were then exposed to OVA via the airways. Additionally, RSV-infected mice were depleted of CD4 or CD8 T cells following acute RSV infection but prior to airway sensitization. Following sensitization, airway responsiveness to inhaled methacholine, numbers of lung eosinophils, and levels of IFN-gamma, IL-4, and IL-5 in PBLN cell cultures were monitored. Transfer of T cells from RSV-infected mice resulted in increased eosinophil influx into the lungs, increased IL-5 production, and development of AHR following airway sensitization to allergen. Transfer of CD8 but not CD4 T cells from the PBLN of RSV-infected mice also resulted in AHR following 10 days of OVA exposure. Further, depletion of CD8 T cells prevented these consequences of RSV infection while CD4 T cell depletion reduced them. We conclude that T cells, in particular CD8 T cells, are critical in mediating RSV-induced development of lung eosinophilia and AHR following allergic airway sensitization.     

Tolerance induced by chronic inhaled antigen in a murine asthma model is not mediated by endotoxin

Ovalbumin (OVA)-sensitized wildtype (WT) and endotoxin-resistant (ER) mice developed similar degrees of airways eosinophilia and serum OVA-specific IgE levels after acute aerosolized OVA challenge. WT mice demonstrated methacholine hyperreactivity, whereas ER mice showed no change in responsiveness. With chronic aerosolized OVA challenge, both WT and ER mice developed local tolerance, with resolution of airway eosinophilia but persistence of anti-OVA IgE in serum. Thus, the development of local tolerance with chronic aerosol exposure to OVA is independent of any potential effects of endotoxin in the OVA aerosol solution.     

Systemic pilocarpine increases deposition of and decreases responsiveness to inhaled carbachol in sheep.

The purpose of this study was to determine whether excessive airway secretions could serve as a barrier function against inhaled particulate matter. To increase airway secretions, six conscious sheep were treated with pilocarpine (0.8 mg/kg i.v.). Pilocarpine increased pulmonary resistance (RL) and total aerosol deposition within five breaths (AD5) as determined by the rebreathing of an inert monodisperse aerosol. When RL had returned to baseline, AD5 remained elevated [21 +/- 2% (SE), P < 0.05] and tracheal secretions were increased (237 +/- 77%, P < 0.05) above the values before pilocarpine administration. A carbachol aerosol dose-response curve was carried out at this time and compared with a control carbachol dose-response curve by calculating the dose of carbachol required to increase RL by 400% (PD400). Mean PD400 was increased postpilocarpine by 53 +/- 18 (P < 0.05) and 85 +/- 25% (P < 0.05) when normalized for increased aerosol deposition. Thus, pilocarpine decreased airway responsiveness to inhaled carbachol despite increasing aerosol deposition. The pilocarpine-induced airway hyporesponsiveness to inhaled carbachol is consistent with the hypothesis that excessive secretions have a protective role in the airways.     

Airway hyperresponsiveness and remodeling in antigen-challenged guinea pigs

Airway hyperresponsiveness (AHR) is the main feature of allergic subjects/animals, and its underlying mechanism is not clear. We explored whether antigen-induced AHR is associated with cytokine generation, inflammatory cell infiltration, and/or remodeling of airway smooth muscle. Guinea pigs were divided into three groups: control-1, control-2, and ovalbumin (OA). Animals in the control-1 group were not sensitized, while those in the control-2 and the OA group were sensitized with OA. Forty to forty-two days after the initial sensitization or equivalent time, animals in the control-2 group inhaled saline aerosol and those in the OA group inhaled OA aerosol for 30 min. Twenty-four h after OA challenge or equivalent time, animals in each group were further divided into two subgroups: methacholine and hyperventilation. Functional tests were carried out before and after the methacholine or hyperventilation treatment. Immediately after the functional study, bronchoalveolar lavage fluid was collected for determination of inflammatory cells and tumor necrosis factor-alpha (TNF-alpha. The trachea was then removed to determine smooth muscle mass. In both the methacholine and hyperventilation subgroups, significantly more severe airway constriction was found in the OA group, indicating OA-induced AHR. Eosinophil accumulation increased in the control-2 group and this increase was further augmented in the OA group. In addition, TNF-alpha level and smooth muscle mass significantly increased in the OA group. These results suggest that OA challenge-induced AHR is associated with increases in TNF-alpha level, cellular infiltration, and airway smooth muscle mass.     

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.