Omalizumab can inhibit respiratory reaction during aspirin desensitization.

BACKGROUND: Aspirin desensitization has been associated with benefit in management of aspirin-exacerbated respiratory disease (AERD). An intervention that would encourage aspirin desensitization to be performed more frequently has substantial potential for improving outcomes and quality of life in patients with AERD. OBJECTIVE: We investigated whether omalizumab administration would be associated with attenuation of aspirin-provoked bronchospasm in patients with AERD undergoing aspirin desensitization. METHODS: We carried out a randomized, double-blind, placebo-controlled study in which subjects with AERD who fulfilled label criteria for omalizumab received omalizumab or placebo for 16 weeks, and then underwent aspirin desensitization. RESULTS: Eleven subjects completed aspirin desensitization. Of the 7 who were randomized to omalizumab, 5 had no respiratory reaction during aspirin desensitization. Compared with placebo, omalizumab was associated with a significantly greater likelihood for subjects with AERD to have no respiratory reaction during desensitization (P = .04, Fisher exact test). There was an overall difference in urinary leukotriene E4 (LTE4) levels in subjects who received omalizumab and did not have a respiratory reaction during desensitization compared with subjects randomized to placebo (P = .035, mixed model with interaction). Urinary LTE4 levels were significantly higher with respiratory reaction in placebo subjects compared with levels obtained after the 100-mg dose in AERD subjects who had no respiratory reaction (P < .001, mixed model with interaction). CONCLUSION: In atopic AERD subjects, omalizumab administration for 16 weeks was associated with "clinically silent" desensitization. Further studies to investigate the therapeutic utility of omalizumab in patients with AERD who are candidates for aspirin desensitization are warranted based on these findings. TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT00555971.

Inhibition of extracellular nucleotides hydrolysis intensifies the allergic bronchospasm. A novel protective role of ectonucleotidases.

BACKGROUND: Nucleotides released to the extracellular space stimulate purinergic receptors, and their effects are modulated by ectonucleotidases. The role of ATP in the allergic bronchospasm has been scantly studied. METHODS: We used several techniques (plethysmography, organ baths, confocal microscopy, RT-PCR, ATP measurement) to explore the role of nucleotides and ectonucleotidases in the allergic bronchospasm in guinea pigs. RESULTS: While allergenic challenge with a low-dose ovalbumin (OVA) only produced a small bronchospasm (~2-fold the basal lung resistance), previous inhibition of ectonucleotidases by ARL-67156 greatly intensified this response (~11-fold the basal lung resistance, with 44% mortality). Bronchoalveolar lavage fluid obtained during this bronchospasm contained increased ATP concentration. This potentiation was abolished by antagonism of purinergic receptors (suramin+RB2) or TXA2 receptor (SQ29548), or by intratracheal apyrase. In tracheal rings and lung parenchyma strips, OVA caused a concentration-dependent contraction. Suramin+RB2 or levamisole produced a significant rightward displacement of this response, and ARL-67156 did not modify it. Platelets stimulated with OVA released ATP. Confocal images of nonsensitized tracheas showed slight fluorescence for P2Y6 receptors in epithelium and none for P2Y4 . Sensitized animals showed strong fluorescence to both receptors and to alkaline phosphatase in the airway epithelium. This correlated with a large increment in mRNA for P2Y4 and P2Y6 receptors in sensitized animals. CONCLUSIONS: Nucleotides greatly potentiate the allergic bronchospasm when ectonucleotidases activity is diminished, and this effect is probably favored by the upregulation of P2Y4 and P2Y6 receptors in airway epithelium during sensitization. These results prompt for further research on these mechanisms in human asthma.

Exhaled RANTES and interleukin 4 levels after exercise challenge in children with asthma.

BACKGROUND: Despite the universality and clinical significance of exercise-induced bronchospasm (EIB), the mechanisms responsible for it are incompletely understood. OBJECTIVE: To investigate the role of exhaled RANTES (regulated on activation, normal T-cell expressed and secreted) and interleukin (IL) 4 in EIB in children with asthma. METHODS: Fifty-six children with asthma were evaluated with exercise challenge and exhaled RANTES and IL-4 levels. Exhaled breath condensate was collected before and 30 minutes after exercise challenge. RANTES and IL-4 concentrations were determined using a specific immunoassay kit. RESULTS: A significant increase was found in RANTES levels after exercise challenge in the asthmatic children (P<.001). A statistically significant increase in RANTES levels was noted after exercise challenge in both the asthmatic children with EIB (n=25, P=.007) and in the non-EIB asthmatic group (n=31, P=.005). Our study revealed that exhaled RANTES level correlates significantly well with percentage of forced expiratory volume in 1 second (FEV1), exacerbation frequency, serum IgE, and body mass index. No statistically significant increase was found in IL-4 levels after exercise challenge. The maximal postexercise decrease in FEV1 strongly correlated with total eosinophil count (P<.001, r = -0.61) and baseline ratio of FEV1 to forced vital capacity (FVC) (P=.002, r=0.40). Results from multivariate regression analysis adjusted for age, sex, and atopy as covariates showed that eosinophil count and FEV1/FVC ratio were significantly associated with EIB. CONCLUSION: We found that exercise challenge, leading to hyperosmolar stimulus, may increase exhaled RANTES levels in children with asthma. In addition, exhaled RANTES levels correlate well with serum IgE, severity of asthma, FEV1/FVC ratio, and body mass index. RANTES and IL-4 may not be independent predictors for EIB. Furthermore, eosinophil count and FEV1/FVC ratio may predict the presence and severity of EIB in asthmatic children.

Suspected recurrent anaphylaxis in different forms during general anesthesia.

We report on a patient who presented with recurrent severe shock during general anesthesia. The patient was a man scheduled for lung surgery whose first attack was a coronary spasm, which was followed by a second shock with severe bronchospasm and hypotension 4 weeks later. An elevated serum tryptase concentration was observed, and subsequent skin testing revealed negative reactions to some drugs administered in this case. This case serves to alert anesthetists to the possibility of some different forms of allergy and highlights the importance of rigorous investigation of all the reagents and phenomena.

Is intrinsic asthma synonymous with infection?

Rackemann described the 'intrinsic asthma' population over 50 years ago as a unique subgroup that was characterized by onset of progressive loss of lung function beginning later in life, possibly after a respiratory infection. It has also been associated with a female predominance, aspirin-sensitive bronchospasm, and nasal polyposis. While the aetiology is not understood, we propose that persistent respiratory infections play a central role in the development of intrinsic asthma.

Influence of brain and behavior on the immune system.

It has been shown experimentally that psychosocial processes influence the susceptibility to some infections, to some neoplastic processes, and to some aspects of humoral and cell-mediated immune responses. These psychosocial effects may be related to hypothalamic activity. Reviewing the mechanisms that may be involved in the role of the hypothalamus in immune responses indicates that there is no single mediating factor. Various processes may participate, including the autonomic nervous system and neuroendocrine activity. The research reviewed has been limited primarily to a consideration of the effect of hypothalamic lesions on humoral immune responses. There is some evidence (45, 80) indicating that hypothalamic lesions also modify cell-mediated immune responses. Further research is required to evaluate the effect of the hypothalamus on cell-mediated immunity.

Depletion of OX-8 lymphocytes from the blood and airways using monoclonal antibodies enhances the late airway response in rats.

Recent evidence supports a role for T lymphocytes in allergic airway responses. We hypothesized that reducing blood T suppressor cells (Ts) might increase the late airway response (LR). Sprague-Dawley (SD) rats were sensitized with ovalbumin (OA). On days 8, 10, and 12, post-sensitization test SD (n = 14) received monoclonal antibody intravenously (OX-8; 1 mg) specific to rat Ts. Controls received saline (n = 7) or mouse ascites IgG (n = 7). On day 14, animals were challenged with OA aerosol (5% wt/vol) for 5 min, lung resistance was recorded for 8 h (n = 18) and bronchoalveolar lavage was performed. The LR was determined from the area under the lung resistance vs time curve from 75 to 480 min after challenge. In the remaining 10 rats, airway lymphocyte subsets were measured 8 h after OA aerosol challenge in minced and digested lungs. A decrease in percentage of blood and airway Ts, respectively, in test animals was observed vs controls (blood: 6.27 +/- 0.84 vs 32.95 +/- 1.94, P < 0.001); (airway: 5.05 +/- 0.66 vs 24.5 +/- 3.05, P < 0.02). Blood and airway helper T lymphocytes did not differ between test and control animals. The LR was significantly increased in test (22.89 +/- 3.92) vs controls (4.22 +/- 2.18, P < 0.001). Bronchoalveolar lavage macrophages, neutrophils and lymphocytes, and serum OA-specific IgE were also significantly elevated (P < 0.05) in test animals. We conclude that Ts play an important role in attenuating the LR in SD rats.

Experience of correcting endothelial dysfunction in children-residents of radioactively contaminated areas by nitric oxide potential donator citrulline. / DOSVID KOREKTsIÏ ENDOTELIAL'NOÏ DYSFUNKTsIÏ U DITEY̆, MEShKANTsIV RADIOAKTYVNO ZABRUDNENYKh TERYTORIY̆, ZA DOPOMOGOIu POTENTsIY̆NOGO DONATORA OKSYDU AZOTU ­ TsYTRULINU.

OBJECTIVE: to determine the effectiveness of citrulline use for correcting endothelial dysfunction in children resi dents of radioactively contaminated areas. MATERIALS AND METHODS: A group of children residents of radioactively contaminated areas with the presence of clinical and paraclinical signs of endothelial dysfunction was selected to assess the effectiveness of correcting endothelial dysfunction by the usage of NO potential donator - citrulline according to the data of selective screen ing. There were determined the biochemical parameters of the content of NO stable metabolites, L arginine, lipid peroxidation, antioxidant enzymes in the blood serum; the indices of cellular and humoral immunity; the instrumen tal indices of vascular endothelium dependent reaction on occlusion test, the lung ventilation capacity, the bioelec tric activity of the myocardium, the autonomic regulation of the cardiovascular system.Examined children were received a course of citrulline malate. RESULTS AND CONCLUSIONS: An increased content of serum L arginine, nitrite, and amounts of NO metabolites was established in children with endothelial dysfunction who were received a course of citrulline malate. Bronchospasm elimination was noted in the significant part of examined patients after the drug use. Decreased recovery period and increased period of hypercompensation for thermographic circulation index in the test with post occlusion reac tive hyperemia were detected by an evaluation of indicators for vascular endothelium dependent vasodilatation using thermographic method indicating an increased endothelial vasomotor capacity. There was tendency to improve the processes of autonomic regulation of the heart rhythm and repolarization of the heart muscle. The antioxidant effect of used citrulline malate course was determined as: decreased content of serum LPO end products that react with thiobarbituric acid under elevated activity of antioxidant - catalase. An increase in the percentage of T lymphocyte, normalization of their subpopulation composition was noted in dynamics of citrulline malate application.

Effects of drug treatment on inflammation and hyperreactivity of airways and on immune variables in cats with experimentally induced asthma.

OBJECTIVE: To compare the effects of an orally administered corticosteroid (prednisone), an inhaled corticosteroid (flunisolide), a leukotriene-receptor antagonist (zafirlukast), an antiserotonergic drug (cyproheptadine), and a control substance on the asthmatic phenotype in cats with experimentally induced asthma. ANIMALS: 6 cats with asthma experimentally induced by the use of Bermuda grass allergen (BGA). PROCEDURES: A randomized, crossover design was used to assess changes in the percentage of eosinophils in bronchoalveolar lavage fluid (BALF); airway hyperresponsiveness; blood lymphocyte phenotype determined by use of flow cytometry; and serum and BALF content of BGA-specific IgE, IgG, and IgA determined by use of ELISAs. RESULTS: Mean +/- SE eosinophil percentages in BALF when cats were administered prednisone (5.0 +/- 2.3%) and flunisolide (2.5 +/- 1.7%) were significantly lower than for the control treatment (33.7 +/- 11.1%). We did not detect significant differences in airway hyperresponsiveness or lymphocyte surface markers among treatments. Content of BGA-specific IgE in serum was significantly lower when cats were treated with prednisone (25.5 +/- 5.4%), compared with values for the control treatment (63.6 +/- 12.9%); no other significant differences were observed in content of BGA-specific immunoglobulins among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Orally administered and inhaled corticosteroids decreased eosinophilic inflammation in airways of cats with experimentally induced asthma. Only oral administration of prednisone decreased the content of BGA-specific IgE in serum; no other significant local or systemic immunologic effects were detected among treatments. Inhaled corticosteroids can be considered as an alternate method for decreasing airway inflammation in cats with asthma.

[Analysis of intracellular cytokines IFN-gamma and IL-4 in peripheral blood T cells in children with bronchospastic reaction]. / Ocena wewnatrzcytoplazmatycznych receptorów cytokinowych IFN-gamma i IL-4 u dzieci z odczynami bronchospastycznymi.

UNLABELLED: In the epidemiological study there was suggested that respiratory tract infections--were a strong risk factors for the beginning and development of bronchial asthma. The aim of the study was the evaluation of intracellular cytokine IL-4 and IFN-gamma on peripheral blood T subsets in children with atopic asthma (AA) and recurrent respiratory tract infection with bronchospasm (RRTI). METHOD: Peripheral blood T cells were stained with fluorescence-labelled antibodies specific for intracellular cytokines IFN-gamma and IL-4 and cell surface markers CD3, CD4 and CD8, and were subjected to flow-cytometric analysis. RESULTS: Comparing peripheral blood lymphocytes of atopic asthma patients with those of recurrent infections we found significantly more cells positive for IL-4 in asthma patients than in recurrent infection patients, both in the CD3+ subsets (p<0.03) and CD4+ subset (p<0.01). We have also found that percentage of CD4+ was significantly lower (p<0.007) and percentage of CD8+ cells was significantly higher (p<0.05) in RRTI group comparing to atopic asthma patients. In AA group there was a significant increase intracellular expression of IL-4 among the CD3+ (p<0.03) and CD4+ (p<0.01) subsets and no significant differences among CD8+ subset. In AA group there was a significant decrease ratio of IFN-gamma/IL-4 among all of the evaluated subsets. CONCLUSION: Basing oneself on these results we conclude that markers of atopy are: increased intracellular expression of IL-4 among CD4+ cells and decreased IFN-gamma.

Synthesis of 3,4-dihydro-4-oxothieno[2,3-d]pyrimidine-2-carboxylates, a new series of orally active antiallergy agents.

A series of novel 3,4-dihydro-4-oxothieno[2,3-d]pyrimidine-2-carboxylic acid derivatives has been prepared and tested for antiallergenic activity. Members of the series, including both carboxylic acid salts and esters, have been found to exhibit oral activity in the rat passive cutaneous anaphylaxis (PCA) test. Activity is optimized by H or CH3 substitution at the 5 position and lower alkyl groups at the 6 position. Ethyl 6-ethyl-3,4-dihydro-4-oxothieno-[2,3-d]pyrimidine-2-carboxylate and 3,4-dihydro-5-methyl-6-(2-methylpropyl)-4-oxothieno[2,3-d]pyrimidine-2-carboxylic acid dipotassium salt were the most potent of the esters and salts, respectively. Such compounds have been shown to have a duration of action of up to 4 h in the PCA test and to inhibit both histamine release from rat peritoneal mast cells in vitro and allergen-induced bronchospasm in the rat lung.

New antihistaminic theophylline or theobromine derivatives.

A series of 3,4-dihydro-1,3-dimethyl-7-[3-(4-substituted-piperazin-1-yl)- substituted-alkyl]-1H-purine-2,6-diones and 3,7-dihydro-3,7-dimethyl-1-[3-(4-substituted-piperazin-1-yl)- substituted-alkyl]-1H-purine-2,6-diones was synthesized and evaluated for antihistaminic activity. Some of them displayed good inhibition of both histamine-induced bronchospasm in the anesthetized guinea pig at 10 micrograms/kg by the intravenous route and of passive cutaneous anaphylaxis in the rat at 10 mg/kg by the oral route. Comparison of the two most active compounds revealed a higher antihistaminic activity with the compounds containing a (phenylthio)propyl group (1 and 2) as compared with that containing a phenoxy group. Compound 2 [RS-49014, 3,4-dihydro-1,3-dimethyl-7-[3-[4-[3-(phenylthio)propyl]piperazin-1 -yl]- 2-hydroxypropyl]-1H-purine-2,6-dione] was selected for clinical trials on the basis of a comparative pharmacological study with chlorpheniramine, ketotifen, promethazine, and theophylline.

Antiallergy activity of substituted 11-oxo-11 H-pyrido[2,1-b]quinazoline-8-carboxylic acids.

A series of substituted 11-oxo-11H-pyrido[2,1-b]quinazoline-8-carboxylic acids were prepared and evaluated as antiallergy agents. Several analogues were orally active. 2-Methyl-11-oxo-11H-pyrido[2,1-b]quinoazoline-8-carboxylic acid (6) was superior to cromolyn sodium and doxantrazole orally and intravenously in the rat PCA test and a rat allergic bronchospasm model.

Antianaphylactic agents. 1. 2-(Acylamino)oxazoles.

The synthesis and biological properties of 35 2-(acylamino)oxazoles are described. The majority of the compounds inhibit the release of slow-reacting substance of anaphylaxis (SRS-A) in vitro from sensitized guinea pig chopped lung. In addition, several of the compounds inhibited the release of SRS-A from passively sensitized human chopped lung and protected guinea pigs from the effects of anaphylaxis in a modified Herxheimer test.

An in vivo model for measuring antigen-induced SRS-A-mediated bronchoconstriction and plasma SRS-A levels in the guinea-pig.

1 Pharmacological modulation of antigen-induced anaphylaxis in actively sensitized guinea-pigs with intravenously administered indomethacin (10 mg/kg), pyrilamine (2.0 mg/kg) and propranolol (0.1 mg/kg) resulted in a delayed onset, slowly developing bronchoconstriction indicative of a slow-reacting substance of anaphylaxis (SRS-A) response. 2 Measurements of pulmonary mechanics on the drug-pretreated animals challenged with ovalbumin demonstrated a more prominent effect on dynamic compliance than resistance. This is consistent with the more potent effects of SRS-A on peripheral rather than central airways. 3 The slowly developing bronchoconstriction obtained after treatment with indomethacin, pyrilamine and propranolol was inhibited by the standard SRS-A antagonist, FPL 55712 and the SRS-A synthesis inhibitors, phenidone, BW 755C and nordihydroguaiaretic acid. 4 Plasma SRS-A levels were determined in guinea-pigs following antigen challenge. The appearance of SRS-A in the plasma preceded the onset of bronchoconstriction and SRS-A levels remained elevated throughout its development. Coincident with the inhibition of bronchoconstriction by the SRS-A synthesis inhibitor, phenidone, was a dose-dependent reduction in plasma SRS-A. The intravenous ED50 in each case was 4 mg/kg. 5 This model of antigen-induced SRS-A-mediated bronchoconstriction should prove useful for the in vivo evaluation and development of therapeutics which regulate the synthesis of SRS-A.

Mechanisms of Forssman-induced bronchospasm and their inhibition.

1 The bronchospasm induced in the guinea-pig by the injection of Forssman antiserum was biphasic in nature in both the sublethal and the lethal reaction. 2 The development of both phases of the bronchospasm in the sublethal reaction was dependent upon the presence of the intact complement system and circulating platelets. In the lethal reaction the phase II bronchospasm did not appear to depend on these factors. 3 The compounds used in this study inhibited phase I bronchospasm of the sublethal reaction in the order, methysergide greater than indomethacin greater than aspirin = sulphinpyrazone and phase II in the order, indomethacin greater than sulphinpyrazone greater than aspirin. Methysergide was inactive. 4 Aspirin, indomethacin and sodium salicylate all prevented the inhibitory action of sulphinpyrazone in reducing the phase II bronchospasm of the sublethal reaction in the order, indomethacin greater than sodium salicylate greater than aspirin, when the drugs were administered prior to sulphinpyrazone. 5 The inhibitory action of aspirin on the sulphinpyrazone effect could be prevented by administering sulphinpyrazone before aspirin. All drug-induced inhibitions of sulphinpyrazone by aspirin, indomethacin and sodium salicylate were dose-dependent.

Effects of theophylline and rolipram on antigen-induced airway responses in neonatally immunized rabbits.

1. The effects of the xanthine, theophylline, a non-selective phosphodiesterase (PDE) inhibitor, and the phosphodiesterase type 4 (PDE 4) inhibitor, rolipram, were evaluated in a model of antigen-induced airway responses in the allergic rabbit. 2. Adult litter-matched NZW rabbits (2.5-3.9 kg), immunized within 24 h of birth with Alternaria tenuis antigen, were pretreated twice daily for 3 days with theophylline (3 mg kg-1, i.p) or rolipram (1 mg kg-1, i.p) prior to antigen challenge (Alternaria tenuis). For each drug-treated group, a parallel group of rabbits were pretreated with the appropriate vehicle. In all groups airway responsiveness to inhaled histamine and bronchoalveolar lavage (BAL) was performed 24 h before and after antigen-challenge. 3. Basal lung function in terms of resistance (RL, cmH2O 1(-1)s-1) and dynamic compliance (Cdyn, ml cmH2O-1) were unaltered by pretreatment with theophylline or rolipram compared to their respective vehicles 24 h prior to or post antigen challenge. 4. The acute bronchoconstriction induced by inhaled Alternaria tenuis aerosol was unaffected by pretreatment with theophylline or rolipram. 5. Airway hyperresponsiveness to inhaled histamine was indicated by reduced RL PC50 (2.4-3.5 fold) and Cdyn PC35 (2.5-2.6 fold) values 24 h after antigen challenge. Treatment with rolipram, but not theophylline, prevented the increase in responsiveness to inhaled histamine 24 h after antigen challenge. 6. Total cells per ml of BAL fluid increased 24 h after antigen challenge due to the recruitment of neutrophils and eosinophils. Antigen-induced increases in pulmonary neutrophils were unaffected; however, eosinophils were reduced 57.5% in theophylline and 82% in rolipram-treated rabbits. 7. Inhalation of Alternaria tenuis aerosol elicits an acute bronchoconstriction, followed 24 h later by an increased responsiveness to inhaled histamine and pulmonary neutrophil and eosinophil recruitment in the immunized rabbit. With the dosing regimes used, both rolipram and theophylline inhibited eosinophil recruitment, whilst only rolipram prevented the development of airway hyperresponsiveness. Neither agent inhibited the acute bronchoconstriction due to inhaled antigen.

Airway hyper- or hyporeactivity to inhaled spasmogens 24 h after ovalbumin challenge of sensitized guinea-pigs.

1. The aim of this study was to determine whether an inhalation of ovalbumin (OA, 10 or 20 mg ml-1) by conscious OA-sensitized guinea-pigs leads to airway hyperreactivity to spasmogens 24 h later. In contrast to most previous studies, the spasmogens (5-HT, methacholine (MCh), U-46619 and adenosine) were administered by inhalation and airway function was measured in conscious guinea-pigs. 2. Guinea-pigs were sensitized by i.p. injection of 10 micrograms OA and 100 mg aluminium hydroxide in 1 ml normal saline; 14-21 days later they were exposed to an inhalation of 5-HT, MCh, U-46619 or adenosine. Specific airway conductance (sGaw) was measured in conscious animals by whole body plethysmography. The spasmogens caused bronchoconstriction, measured as a reduction in sGaw from the pre-inhalation basal values. Dose-related bronchoconstrictions were observed with 5-HT, MCh and U-46619. 3. The effect of an ovalbumin macroshock challenge upon the responses to each spasmogen were examined by giving an inhalation of aerosolized OA at 24 h (or 7 days in the cause of adenosine) after an initial spasmogen challenge. Eighteen to twenty-four hours after the OA macroshock, the same guinea-pigs were exposed to a repeated inhalation of 5-HT, MCh, U-46619 or adenosine. 4. U-46619 was the only spasmogen to demonstrate hyperresponsiveness, the peak change in sGaw being increased from -12.3 +/- 9.9 to -38.8 +/- 5.0% by 10 mg ml-1 OA challenge. In contrast, the ovalbumin challenge (20 mg ml-1) inhibited the bronchoconstrictions to 5-HT (50 micrograms ml-1) and MCh (100 micrograms ml-1). Adenosine demonstrated bronchoconstriction in sensitized guinea-pigs but no significant change in the response was observed after an OA challenge. 5. All results were compared with a control group of sensitized guinea-pigs receiving a NaCl challenge. The bronchoconstrictor responses to 5-HT, MCh, U-46619 or adenosine did not differ significantly before and after the saline challenge, indicating reproducibility of the responses. 6. In further experiments, guinea-pigs were exposed to inhalation of 5-HT (50 micrograms ml-1) or MCh (300 micrograms ml-1) 24 h before atropine (10 micrograms, 100 micrograms or 1 mg ml-1) and again at 0.5 to 1.5 h afterwards. Atropine, antagonized the 5-HT- and MCh-induced bronchoconstrictions over the same antagonist dose-range. This suggests that the bronchoconstriction induced in the conscious guinea-pig by 5-HT is mediated primarily via muscarinic receptors, possibly by a vagal reflex. The inhibition of the responses to 5-HT and MCh by OA challenge would therefore appear to be related to interference with a common cholinergic pathway for these spasmogens. 7. In summary, airway hyperresponsiveness was evident at 24 h after OA challenge as measured by an enhanced bronchoconstrictor response to inhaled U-46619. When 5-HT or MCh were used as the spasmogens, an opposing decrease in responsiveness was observed. This was presumed to be due to an inhibition of cholinergic pathways by the OA challenge. Adenosine caused a bronchoconstriction in the sensitized animals but this was not enhanced by the OA challenge.