Localization of quantitative changes in pulmonary beta-receptors in ovalbumin-sensitized guinea pigs

Association of asthma with beta(2)-adrenergic receptor gene polymorphism and cigarette smoking

Recent studies have suggested that two polymorphisms of the beta(2)-adrenergic receptor (beta(2)AR) gene at codons 16 (arginine to glycine) and 27 (glutamine to glutamate) affect an individual's airway responsiveness, or response to acute or chronic beta(2)-agonist therapy but are not risk factors for asthma. We hypothesize that there is an interaction effect on asthma between the beta(2)AR gene polymorphisms and cigarette smoking. A case-control study was conducted in 128 asthma cases and 136 control individuals identified from 10,014 studied subjects in rural Anqing, China. Allele-specific polymerase chain reaction (PCR) was used to genotype beta(2)AR gene polymorphisms. Multiple logistic regression was used to adjust for potential confounding factors. We found a marginally significant interaction between cigarette smoking and beta(2)AR-16 genotype after adjusting for important confounding factors (p = 0.06). Specifically, we found that compared with never-smoking Gly-16 homozygotes, those ever-smokers who are Arg-16 homozygotes had a significantly increased risk of asthma (odds ratio [OR] = 7.81; 95% confidence interval [CI]: 2.07 to 29.5). This association showed a clear dose-response relationship with the number of cigarettes smoked. However, there was no significant association of asthma with polymorphisms of the beta(2)AR at position 27 (OR = 1.38; 95% CI: 0.69 to 2.73). Our study suggests a gene-environment interaction between the Arg-16 genotype and ever cigarette smoking with respect to the susceptibility of an individual to asthma.

Intratracheally applied rSP-C surfactant exhibits no anaphylactic shock reactions in a guinea pig model of acute lung hypersensitivity

The effect of the intratracheal administration of the recombinant SP-C surfactant apoprotein (rSP-C) with phospholipids (PL) in comparison to an ovalbumin induced anaphylactic shock reaction was studied in guinea pigs lungs. Narcotized guinea pigs were challenged by intratracheal administration on test day 24/25 once with a suspension of rSP-C/PL (reconstituted suspension). These animals were priorily sensitized on test day 1, 3 and 5 intraperitoneally with rSP-C/PL suspension or with Ovalbumin (OV) respectively. The following groups were used to assess the anaphylactic lung shock symptoms: group 1: positive control, 1 mg/kg OV protein, 2 ml/kg application volume, (Appl. vol.), N: 5 animals; group 2: 1 mg rSP-C/50 mg PL/0.5 ml/kg Appl. vol., N: 10; group 3: 2 mg rSP-C/100 mg PL/1.0 ml/kg Appl. vol., N: 10; group 4: 4 mg rSP-C/200 mg PL/2.0 ml/kg Appl. vol., N: 10. Clinical signs, mortality, lung weights and histopathological changes were evaluated. Additionally the lungs were investigated immunohistologically with polyclonal antibodies against rSP-C to determine the pulmonary distribution of the intratracheal applied rSP-C. In the OV-treated positive control group, all animals died within 4 minutes after intratracheal challenge, while only 1 animal of group 4 died probably due to an narcosis related respiratory arrest. In the rSP-C/PL treated groups, the lung weights showed a dose-related increase, but nevertheless all these rSP-C-treated groups showed a significant lower lung weight in comparison to the OV treated positive control group. The histopathology assessment of the lungs in the OV-treated animals revealed a severe generalised bronchoconstriction and a hyperemia in connection with a slight interstitial edema in all five animals. The rSP-C/PL-treated animals, which were sacrificed after 3 days, showed no bronchoconstriction but a slight increase in the severity of bronchus-associated infiltration with eosinophilic granulocytes and in the formation of peripheral emphysema, but with no dose-dependency. A slight dose-dependent increase in the deposition of peribronchiolar eosinophilic foreign material was evident. In contrast to this, the number of lipid-laden alveolar macrophages seemed to decrease with increasing doses of rSP-C/PL. The immunohistological investigation with a polyclonal antibody against rSP-C showed an intraalveolar distribution of the intratracheally applied rSP-C which is mainly located in the peribronchiolar alveolar parenchyma. A rSP-C-positive staining was visible within the cytoplasm of alveolar histiocytes, type II pneumocytes and also as an extracellularly rim along the alveolar walls. The polyclonal antibody showed no cross reaction with natural occuring SP-C-protein of the guinea pigs. We conclude that the intratracheal application of the rSP-C surfactant containing phospholipids (PL) exhibits no significant risk of an anaphylactic shock reaction in this guinea pig lung hypersensitivity model. The immunohistological investigation with polyclonal antibodies against rSP-C demonstrated clearly the distribution of intratracheal applied material in this toxicological animal model.

Effect of beta 2-agonists on histamine-induced airway microvascular leakage in ozone-exposed guinea pigs

beta 2-adrenergic agonists exhibit antipermeability effects in the airways. However, it is not known whether beta 2-agonists have this beneficial effect in airway mucosa that is already inflamed. We evaluated the effects of two inhaled beta 2-agonists, salbutamol and formoterol, on the histamine-induced bronchoconstriction and plasma extravasation in the airways of guinea pigs with or without ozone exposure. Total pulmonary resistance (RL) was measured before and after histamine inhalation in anesthetized animals that were pretreated with inhaled salbutamol, formoterol, or saline. Plasma extravasation in the airways was measured using Evans blue dye. In the control animals not exposed to ozone, salbutamol and formoterol each significantly reduced both the histamine-induced bronchoconstriction and the plasma extravasation in the trachea and main bronchi. In the ozone-exposed animals, the increase in RL after histamine was greater than that in control animals. Salbutamol and formoterol each significantly reduced histamine-induced bronchoconstriction, even in the ozone-exposed animals. Salbutamol did not affect the histamine-induced plasma extravasation, whereas formoterol reduced the plasma extravasation in the main bronchi, but not in the trachea, of the animals exposed to ozone. These results suggest that the anti-inflammatory properties of formoterol in inflamed airways may contribute to the beneficial effects in the treatment of airway inflammation.

Acute bacterial pneumonia in rats increases alveolar epithelial fluid clearance by a tumor necrosis factor-alpha-dependent mechanism

To study the rate and regulation of alveolar fluid clearance in acute pneumonia, we created a model of Pseudomonas aeruginosa pneumonia in rats. To measure alveolar liquid and protein clearance, we instilled into the airspaces a 5% bovine albumin solution with 1.5 microCi of 125I-human albumin, 24 h after intratracheal instillation of bacteria. The concentration of unlabeled and labeled protein in the distal airspaces over 1 h was used as an index of net alveolar fluid clearance. Since there was histologic evidence of alveolar epithelial injury, several methods were used to measure alveolar fluid clearance, including the use of experiments in rats with blood flow and the use of experiments in rats without blood flow, so that movement across the epithelial barrier would be minimized in the latter group. The results with each method were identical. We found that P. aeruginosa pneumonia increased alveolar liquid clearance over 1 h by 48% in studies with blood flow, and by 43% in rats without blood flow, compared with respective controls (P < 0.05). In both studies, this increase was inhibited with amiloride. However, propranolol had no inhibitory effect, thus ruling out a catecholamine-dependent mechanism to explain the increase in alveolar fluid clearance. An antitumor necrosis factor-alpha neutralizing antibody, instilled into the lung 5 min before bacteria, prevented the increase in alveolar liquid clearance in rats with pneumonia (P < 0.05). Also, TNFalpha (5 microg) instilled in normal rats increased alveolar liquid clearance by 43% over 1 h compared with control rats (P < 0.05). In normal rats instilled with TNFalpha, propranolol had no inhibitory effect. In conclusion, gram-negative pneumonia markedly upregulates net alveolar epithelial fluid clearance, in part by a TNFalpha-dependent mechanism. This finding provides a novel mechanism for the upregulation of alveolar epithelial sodium and fluid transport from the distal airspaces of the lung.

Effects of in vitro mast cell degranulation on human lung beta-receptor binding parameters

BACKGROUND

Numerous studies have demonstrated that subjects with allergic asthma have beta-adrenergic hyporesponsiveness, predisposing these individuals toward bronchospasm, mucous production, and mast cell degranulation. Since sympathetic innervation of the human respiratory tract is sparse, reduced beta-responsiveness probably results from alterations at or beyond the receptor level.

OBJECTIVE

We therefore examined whether anaphylaxis of human lung tissue acutely modulated the human lung beta-receptor system in ways that might lead to decreased beta-adrenergic responsiveness.

METHODS

Fresh thoracotomy peripheral lung samples from 26 patients were incubated with (anaphylaxis) or without (control) anti-IgE (1:100) for up to 90 minutes and histamine release was documented. Lung fragments were quick frozen at various times after anti-IgE for analyses of beta-receptor binding parameters. Antagonist Kd (dissociation constant) and receptor concentration values were determined using (-)[125I]pindolol and agonist IC50 values were determined using isoproterenol.

RESULTS

In comparison with time O, neither anaphylaxis nor control samples had differences in receptor binding parameters with time. There were also no differences between anaphylaxis and control lung samples at any time point, and ratios of log control binding parameter/log anaphylaxis binding parameter ranged from 0.96 to 1.01.

CONCLUSIONS

Anaphylaxis of lung does not lead to acute changes in antagonist or agonist affinity for beta-receptors or changes in receptor concentration. Under the conditions studied, lung mast cell degranulation does not acutely alter the human lung beta-receptor system in ways that might account for the beta-adrenergic hyporesponsiveness found in allergic asthma.

Acetylcholine-induced bronchoconstriction modified by noise exposure in normal but not in sensitized guinea-pigs

1. The acute (6h) exposure of guinea-pigs to white noise (110 dB) as a stress stimulus, reduced bronchial reactivity to acetylcholine (Ach) (3-1000 micrograms kg-1 i.v.) in anaesthetized animals. 2. The hyporesponsiveness to Ach in stressed animals was not confirmed in vitro on tracheal preparations (Ach 1 x 10(-9)-1 x 10(-4) g ml-1) and disappeared in vivo when the animals were sensitized with ovalbumin (OA, 100 mg kg-1 i.p. + 100 mg kg-1 s.c.). The hyporesponsiveness was also absent in ovalbumin sensitized guinea-pigs exposed to an aerosol of ovalbumin 60 min before testing with Ach. 3. In non-sensitized guinea-pigs, pretreatment with butoxamine (1 mg kg-1 i.v.) or with theophylline (25 mg kg-1 i.v.), completely abolished the effect of noise-exposure. In contrast, pretreatment with L-NG-nitro-arginine methyl ester (L-NAME, 10 mg kg-1 i.v.), alpha-chymotrypsin (2 U kg-1 i.v.) or with enprofylline (10 mg kg-1 i.v.), did not affect it. 4. In conclusion, our experiments reveal inhibitory mechanisms upon Ach-induced bronchoconstriction activated by a stress stimulus and this is absent in sensitized animals. These mechanisms seem to be linked to the adrenergic beta 2-receptors and a role for the purinergic system (via A-receptors) may also be present.

Beta-adrenoceptor regulation and functional responses in the guinea-pig following chronic administration of the long-acting beta 2-adrenoceptor agonist formoterol

Formoterol is a long acting beta 2-adrenoceptor agonist designed for the alleviation of the symptoms of asthma. This study examined the effects of 14 day administration of formoterol (200 micrograms/kg/day i.p.) on beta 1- and beta 2-adrenoceptors in guinea-pig cardiac and lung tissue. Quantitative autoradiography was used to measure changes in receptor density and organ bath studies determined alterations in functional response. Formoterol treatment produced marked reductions of between 43% and 77% in beta 2-adrenoceptor density in all regions of the heart (atrioventricular node, bundle of His, right and left bundle branches, interventricular and interatrial septa, right and left atria, ventricles and apex) and lung (bronchial and vascular smooth muscle and parenchyma) (P < 0.01, n = 6). beta 1-Adrenoceptor density remained unchanged in all cardiac and lung regions. In functional studies (-)-isoprenaline was 4 fold less potent at causing relaxation of carbachol (1 microM) precontracted tracheal smooth muscle (pD2: control 8.49 +/- 0.03, formoterol 7.91 +/- 0.10, P < 0.001, n = 4), but formoterol treatment did not change the ability of (-)-isoprenaline to elicit a maximum response. The pKB values for ICI 118,551, 7.33 +/- 0.08 in the control and 7.20 +/- 0.01 in formoterol treated animals, were between those expected for beta 1- and beta 2-adrenoceptors suggesting involvement of both subtypes in the response. In spontaneously beating right atria and electrically paced left atria, tissues in which responses are largely mediated by beta 1-adrenoceptors, there was no significant change in responses to (-)-isoprenaline (right atria pD2: control 8.45 +/- 0.02; formoterol 8.42 +/- 0.11; P = 0.77, n = 4) (left atria pD2: control 8.25 +/- 0.03; formoterol 8.47 +/- 0.08; P = 0.09, n = 4). In the presence of CGP 20712A (100 nM) the pKB values did not change with formoterol treatment (left atria: control 9.59 +/- 0.12, formoterol 9.66 +/- 0.12; P = 0.70, n = 4) (right atria: control 8.93 +/- 0.11, formoterol 9.11 +/- 0.07; P = 0.25, n = 4). The doses and route of administration of formoterol used in this study differs from those used clinically. However, this study demonstrates that chronic formoterol administration produces selective down-regulation of beta 2-adrenoceptors in the lung and heart. The changes in the lung are accompanied by a shift to the right in the concentration-response curve to beta-agonist stimulation with no change in the maximum response.

High affinity [3H]formoterol binding sites in lung: characterization and autoradiographic mapping

Agonist binding to the beta 2-adrenoceptors and its mapping were studied using the newly developed radioligand [3H]formoterol. The results of [3H]formoterol saturation binding and formoterol inhibition of [3H]formoterol binding were consistent with binding to a single class of receptors (Kd = 1.34 +/- 0.15 nM, Bmax = 154.9 +/- 8.0 fmol/mg protein in guinea pig lung membranes, n = 8; Kd = 1.05 +/- 0.17 nM, Bmax = 67.8 +/- 8.1 fmol/mg protein in human lung membranes, n = 5) and competition assays with other agonists and antagonists disclosed only a single class of site. The nonhydrolyzable GTP analogue GTP gamma S caused a reduction in both Kd and Bmax, indicating that the receptors labelled by [3H]formoterol are coupled to a guanine nucleotide binding regulatory protein. Receptor mapping of [3H]formoterol binding sites shows that beta 2-adrenoceptors were widely distributed in both guinea pig and human lung, with dense labelling over airway epithelium and uniformly over alveolar walls, and sparse labelling of airway and vascular smooth muscle. In addition, submucosal glands were also sparsely labelled in human bronchus. The distribution of beta 2-adrenoceptors was similar to the pattern previously described with non-selective radiolabelled antagonists in the presence of selective beta 1-adrenoceptor antagonists.

Genetic polymorphism of the beta-2 adrenergic receptor in atopic and non-atopic subjects

To investigate a possible genetic basis for reported differences in beta-2 receptor expression in atopic subjects, DNA from 42 atopic children (22 asthmatics and 22 with allergic rhinitis) and 30 non-atopic subjects was Southern blotted and Ban-1 restriction fragment polymorphisms (RFLPS) were studied using a 2.6 kb probe of the human beta-2 receptor gene. Two alleles 3.1 kb and 2.9 kb were identified. Homozygotes and heterozygotes for the two alleles were found with equal frequency in the atopic patients who had asthma and in those who had allergic rhinitis only. The gene frequencies for the upper and lower alleles were 0.45 and 0.55 respectively. Our studies do not provide evidence for an association between a particular polymorphic form of the human beta-2 receptor gene and atopy.

Mutations in the gene encoding for the beta 2-adrenergic receptor in normal and asthmatic subjects

It has long been hypothesized that a defective beta 2-adrenergic receptor (beta 2AR) may be a pathogenic factor in bronchial asthma. We examined the gene encoding the beta 2AR to assess the frequency of polymorphisms in 51 patients with moderate to severe asthma and 56 normal subjects. Nine different point mutations were found in both heterozygous and homozygous forms at nucleic acid residues 46, 79, 100, 252, 491, 523, 1053, 1098, and 1239. No mutations resulting in large deletions or frame shifts were detected. Of these nine polymorphisms, four were found to cause changes in the encoded amino acids at residues 16, 27, 34, and 164. The most frequent polymorphisms were arginine 16 to glycine (Arg16-->Gly) and glutamine 27 to glutamic acid (Gln27-->Glu). The other two polymorphisms, valine 34 to methionine, and threonine 164 to isoleucine, occurred in only four subjects. The incidence of beta 2AR homozygous polymorphisms was no greater in asthmatic patients as compared with controls (Arg16-->Gly: 53% versus 59%, Gln27-->Glu: 24% versus 29%, respectively; P = NS). Some subjects were found to have both of these polymorphisms simultaneously, but there was no difference in incidence between the two groups, with 23% of asthmatics and 28% of normal subjects being homozygous for both polymorphisms. The apparently normal subjects with both polymorphisms did not have subclinical hyperreactive airways disease as determined by methacholine challenge testing. In the asthma group, one mutation (Arg16-->Gly) identified a subset of patients with a distinct clinical profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenoceptors and the epithelial layer in airways

As an inflammatory disorder of the respiratory system, asthma is characterized by bronchial hyper-responsiveness that appears to involve alterations of the bronchial epithelium. The existence of epithelial beta-receptors is of particular importance to respiratory function, and epithelial dysfunction in asthma may impair beta-adrenoceptor function and lead to bronchial hyper-responsiveness. After reviewing the structure and function of the respiratory epithelium and the role of epithelial beta-adrenoceptors, an in vitro model allowing the detailed study of the regulation of airway smooth muscle by epithelial cells is described. Studies with this model have demonstrated that epithelial beta-adrenoceptors participate in modulating the tone of bronchial smooth muscle cells. Activation of these beta-adrenoceptors leads to bronchial myorelaxation, probably mediated by one or more inhibitory substances generated within the epithelium. In addition, beta-adrenoceptor activity may affect smooth muscle tone indirectly by regulating mucociliary clearance and the paracellular exchange of inflammatory mediators. Since some respiratory diseases seem to be associated with beta-adrenoceptor dysfunction, therapy with beta-agonists may be beneficial by acting on beta-adrenoceptors located both on smooth muscle cells and on epithelial cells.

Localization of beta 2-adrenoceptor messenger RNA in human and rat lung using in situ hybridization: correlation with receptor autoradiography

We have used in situ hybridization to study the localization of mRNA encoding the beta 2-adrenoceptor in tissue sections of the human and rat lung and compared this with the distribution of beta 2-receptor binding sites using receptor autoradiography. To localize beta 2-receptor mRNA, a [32P]labeled antisense RNA probe (riboprobe) was generated from human or rat beta 2-receptor cDNA. A similar distribution of beta 2-receptor mRNA was identified in both species. The highest intensity of beta 2-receptor mRNA was detected in smooth muscle of small airways, airway epithelium and pulmonary blood vessels. Lower intensity of beta 2-receptor mRNA was identified in smooth muscle of large airways, and alveolar epithelium (presumably type I and type II pneumocytes). No significant hybridization signal was detected in interstitial tissue. The specificity of the hybridization signal was confirmed with a sense probe (having identical sequence to the mRNA) and preincubation with RNase A, and by Northern blot analysis which revealed a single band of mRNA of 2.2 kb. There was a correspondence between mRNA localization and the distribution of beta 2-receptors visualized by [125I]iodocyanopindolol autoradiographically in the presence of CGP 20712 (a beta 1-selective antagonist). However, alveolar walls that showed a high beta 2-receptor density had relatively low levels of mRNA. This cellular heterogeneity may reflect differences in RNA stability or transcription rate in different lung cells. This approach opens up new options in the investigation of the regulation of pulmonary beta 2-receptor gene expression in health and disease.

Effect of sensitization and aerosol antigen challenge in guinea-pigs--studies of airway receptor function and characteristics

Immunological sensitization of guinea-pigs and subsequent antigen inhalation challenge has provided an animal model which has several features in common with human asthma. Impairment of beta-adrenoceptor-mediated function and mechanisms have been postulated to contribute to the hyperreactivity to contractile agonists demonstrated in vivo and in vitro in these animals. Functional and receptor radioligand binding studies were carried out on airway tissue from: non-sensitized; sensitized; sensitized saline challenged; sensitized antigen challenged guinea-pigs. Sensitization did not alter responsiveness of airway tissue to carbachol, although subsequent antigen challenge did increase carbachol sensitivity of peripheral airway tissue six-fold. Neither sensitization itself nor subsequent antigen challenge altered binding characteristics of the muscarinic cholinoceptor ligand [3H]quinuclidinyl benzilate ([3H]QNB) to peripheral airway tissue, suggesting that mechanisms responsible for increases in carbachol sensitivity are distal to these receptors. Relaxation of airway preparations to isoprenaline was not altered by sensitization or further antigen challenge of the animals. However, sensitization significantly reduced affinity but not the total number of binding sites in peripheral airway tissue for the beta-adrenoceptor ligand [3H]dihydroalprenolol ([3H]DHA). Antigen challenge of the animals did not further alter beta-adrenoceptor ligand binding characteristics. These results suggest that airway hyperreactivity in this model is not a function of alteration in receptor characteristics, or impairment of relaxation mechanisms.

Photoaffinity labeling of the guinea pig pulmonary mast cell beta-adrenergic receptor

Beta-adrenergic agonists can prevent mediator release from guinea pig pulmonary mast cells. By pharmacologic characterization, this response is mediated through a beta-2 receptor. Structural characterization of this receptor on the lung mast cell, however, has been limited by methods for isolation of this pulmonary cell. In this study, the guinea pig lung mast cell was isolated to greater than 90% purity, and its beta-adrenergic receptor identified by photoaffinity labeling with [125I]iodoazidobenzylpindolol (125IABP) and separation of membrane proteins by SDS-PAGE. We found the guinea pig pulmonary mast cell beta-adrenergic receptor to electrophorese as a heterogeneous protein between 68 and 116 kD. Photoaffinity labeling with 125IABP was protectable by alprenolol and isoproterenol but not by phentolamine and norepinephrine. Using subtype-selective compounds, the pulmonary mast cell receptor was established to be of a beta-2 subtype. This is the first report of the structural identification of a lung mast cell beta-adrenergic receptor and the first report of a beta-adrenergic receptor of approximately 100 kD in mass. This mast cell receptor is considerably larger than the 65 kD beta-adrenergic receptors that have been identified in whole lung and other tissues. Data we have obtained using Northern blot analysis of mast cell RNA suggest a protein message of 45 kD for this beta-adrenergic receptor and a high degree of glycosylation most likely accounts for the large molecular size observed.

Autoradiographic localization of changes in pulmonary beta-adrenoceptors in an animal model of atopy

Vaccination of guinea pigs with Haemophilus influenzae leads to an impairment of beta-adrenoceptor function in lung. We have used an autoradiographic technique to study the distribution of changes in lung beta-adrenoceptor density. H. influenzae induced a decrease in beta-adrenoceptors in peripheral lung membranes of 22 +/- 5% (mean +/- S.E.M., n = 7), while the affinity of binding was unaffected. Tracheal beta-adrenoceptor binding was not influenced by H. influenzae. Autoradiography revealed a 27% reduction in beta-adrenergic binding sites on alveolar septa. Bronchial epithelial beta-adrenoceptors were decreased for 36%, and vascular smooth muscle and endothelial beta-adrenoceptors were also reduced. beta-Adrenoceptors on airway smooth muscle were unaffected. H. influenzae affected both the beta 1- and beta 2-subtypes of receptors. It is concluded that in this animal model of atopy beta-adrenoceptors may be decreased on several different cell types within the lungs, which may influence overall airway and vascular reactivity.

Immediate anaphylactic bronchoconstriction induces airway hyperreactivity in anaesthetized guinea-pigs

1. The possible acute occurrence of airway hyperreactivity after immediate-type bronchial anaphylaxis has been investigated in anaesthetized guinea-pigs actively sensitized to ovalbumin (OA). 2. Aerosol challenge (OA 10 mg ml-1, 5 s) provoked immediate bronchoconstriction which was substantially, although incompletely, reversed by isoprenaline (Iso) infusion (1 microgram kg-1 min-1) for 10 min). 3. Bronchoconstrictor responses to 5-hydroxytryptamine (5-HT) were enhanced in challenged animals when compared to those in non-challenged animals that had also received Iso. This was seen as a leftward shift in the location of the dose-response curve for the bronchoconstrictor effect of 5-HT (dose-ratio 2.45, 95% confidence limits 1.77-3.38; P less than 0.01). This phenomenon was associated with pulmonary infiltration of polymorphonuclear leukocytes, which was not modified by Iso treatment. 4. Iso infusion alone caused a slight enhancement of airway reactivity seen as a small leftward shift of the dose-response curve for the bronchoconstrictor effect of 5-HT (dose-ratio 1.51, 95% confidence limits 1.07-2.13; P less than 0.05). 5. These results support a causal relationship between acute pulmonary inflammation and airway hyperreactivity in an animal model of human allergic asthma.