Pharmacological characterization of mediators and vagal influence in the acute allergic bronchoconstriction in guinea pigs

Effect of vagotomy on airway hyperreactivity to endogenously released neurotransmitters at 18-24 h after inhaled antigen

Airway reactivity was examined in anaesthetized guinea-pigs 18-24 h after inhalation challenge of ovalbumin-sensitized animals with ovalbumin. Bronchoconstrictor responses were measured from the increases in pulmonary inflation pressure. The study was undertaken to examine whether ovalbumin challenge induced airway hyperreactivity to neurotransmitters released endogenously by vagal nerve stimulation. Stimulation parameters were selected to cause release of either acetylcholine (0.3 ms pulse width for 3 s, 20 V, 2-40 Hz), both acetylcholine and neuropeptide (5 ms pulse width for 15 s, 20 V, 0.5-8 Hz) or neuropeptide only, using the latter parameters in the presence of atropine. The vagi were paired for stimulation and in some experiments were cut central to the stimulation point. Frequency-response curves for acetylcholine- and neuropeptide-mediated bronchoconstrictor responses to vagal stimulation when the nerves were intact revealed no airway hyperreactivity after ovalbumin challenge. The presence of atropine failed to reveal airway hyperreactivity. However, when the vagi were cut, the frequency-response curves were displaced to the left after ovalbumin challenge compared with saline challenged animals, indicating airway hyperreactivity. This airway hyperreactivity was significant after atropine and suggests an increase in sensitivity to endogenously released neuropeptides rather than acetylcholine. It also indicates that the airway hyperreactivity is dependent on removal of the afferent vagal pathways. Frequency-response curves for cholinergic stimulation (0.3 ms) with intact vagi revealed no airway hyperreactivity after antigen challenge. Comparisons of exogenously administered 5-hydroxytryptamine (5-HT, 300 ng/100 g i.v.) and a single vagal stimulation of 0.3 ms pulse width (cholinergic) revealed no airway hyperreactivity to either stimulus after ovalbumin challenge. However if the vagi were cut, airway hyperreactivity was observed, again suggesting that removal of afferent pathways is important for revealing airway hyperreactivity in the anaesthetized guinea-pig. Ovalbumin challenge caused significant increases in the bronchoconstrictor responses to a single dose of capsaicin (50 microg/100 g i.v.) or dose-response curves to bradykinin. Since these agents release neuropeptides from sensory C-fibres, this is further support for a raised sensitivity to endogenously released neuropeptides.

Neural reflex-mediated tracheal response during bronchoconstriction induced by ovalbumin antigen in guinea pigs

1. The biphasic reflex tracheal response (constriction followed by dilatation) occurred during bronchoconstriction induced by inhalation of ovalbumin antigen (OA) in sensitized guinea pigs. 2. The reflex tracheal constriction was largely reduced by atropine, and the dilatation was inhibited by propranolol and N omega-nitro-L-arginine methyl ester (L-NAME). The noradrenaline, adrenaline, cyclic AMP, and cyclic GMP contents in the tracheal segment were significantly higher during reflex tracheal dilatation. 3. These findings suggest that cholinergic nerves may mediate reflex tracheal constriction and that adrenergic and NOergic nerves may mediate the ensuing reflex tracheal dilatation.

Inhaled Bordetella pertussis vaccine decreases airway responsiveness in guinea pigs

Bordetella pertussis (BP) has been used as adjuvant for experimental animal immunization, but its effects on airway responsiveness are uncertain. Three groups of guinea pigs were used: animals with a single exposure to inhaled BP vaccine (strain 134, total dose 1.24 x 10(12) germs), animals submitted to a sensitization procedure through inhalation of ovalbumin plus BP, and healthy control animals. Four weeks after inhalation of BP or after the beginning of sensitization, dose- or concentration-response curves to histamine were constructed in vivo and in vitro (tracheal and parenchymal preparations). We found that BP alone produced lower responses to histamine than control guinea pigs in vivo (insufflation pressure, p = 0.0003) and in tracheal tissues (p = 0.04), but not in parenchymal preparations. Sensitization did not modify the responsiveness compared with their respective controls. These results suggest that some BP component(s), probably pertussis toxin, causes a long lasting airway hyporesponsiveness in guinea pigs.

Effect of ozone exposure on antigen-induced airway hyperresponsiveness in guinea pigs

Airway hyperresponsiveness can be induced by several stimuli including antigen and ozone, both of which may be present in the air of polluted cities. Though the effect of ozone on the bronchoconstrictor response to antigen has been well described, the combined effect of these stimuli on airway hyperresponsiveness has not yet been studied. Sensitized guinea pigs with or without ozone exposure for 1 h at 3 ppm, 18 h prior to study, were challenged with a dose-response curve to histamine (0.01-1.8 micrograms/kg, iv) followed by an antigen challenge (ovalbumin, 50 micrograms/kg, iv), and then by a second histamine dose-response curve 1 h later. Airway responses were measured as the increase in pulmonary insufflation pressure. In sensitized guinea pigs, the histamine ED50 significantly decreased after antigen challenge, demonstrating the development of airway hyperresponsiveness. Sensitized guinea pigs exposed to ozone showed airway hyperresponsiveness to histamine when compared with nonexposed animals, and such hyperresponsiveness was further enhanced after antigen challenge. We conclude that in this guinea pig model of acute allergic bronchoconstriction both antigen challenge and ozone induce airway hyperresponsiveness, while ozone exposure does not modify the development of antigen-induced hyperresponsiveness.

Immediate inhibitory effect of methylprednisolone suleptanate (U-67590A) on antigen-induced cutaneous and airway anaphylactic responses in guinea-pigs

1. Inhibitory effects of water-soluble glucocorticoids administered intravenously were examined on skin and airway reactions caused by antigen challenge or chemical mediators in guinea-pigs. 2. Methylprednisolone suleptanate (U-67590A) which is an analogue of methylprednisolone, produced immediate inhibition of 3-h and 7-day homologous passive cutaneous anaphylaxis (PCA) reactions, but not of histamine- or bradykinin-induced cutaneous vascular permeability, when administered 10 min before antigen challenge. In contrast, methylprednisolone succinate (MP) or dexamethasone (DXM) administered 10 min before antigen challenge failed to show an immediate inhibitory effect on the PCA or mediator-induced reactions. When administered 1 to 5 h before antigen challenge, all the steroids used in this study reduced both PCA and mediator-induced reactions. 3. Pretreatment with cycloheximide almost completely abolished the late inhibition of 3-h PCA and histamine reactions produced by U-67590A or MP, but it did not affect the immediate inhibition of 3-h PCA produced by U-67590A. 4. U-67590A also demonstrated immediate inhibitory effects on antigen-induced bronchoconstriction in guinea-pigs actively sensitized with ovalbumin even when administered 10 min before antigen challenge, whereas MP and DXM failed to show the immediate inhibitory effect. When administered 3 h before antigen challenge, all the steroids used in this study reduced the response to antigen. 5. The late inhibitory effect of U-67590A administered 3 h before antigen challenge was almost completely abolished by treatment with cycloheximide or 17 alpha-methyltestosterone, whereas the immediate inhibition produced by U-67590A administered 10 min before challenge was not affected by this treatment. 6. U-67590A administered 10 min or 3 h before challenge did not affect the bronchoconstriction induced by histamine or leukotriene D4.7. Release of histamine from lung fragments of sensitized guinea-pigs in vitro was inhibited by U-67590A.8. The present experiments indicate that U-67590A demonstrated dual, immediate and late, inhibitory effects. The former are independent of protein synthesis and may be associated with non-genomic direct action on the mediator-releasing process without affecting mediator-induced reactions. The latter share common inhibitory actions with other glucocorticoids which are dependent on protein synthesis through gene expression.

Pharmacologic modulation of antigen-induced pulmonary responses in the perfused guinea pig lung

The effect of various enzyme inhibitors and receptor antagonists on antigen (ovalbumin)-induced changes in pulmonary hemodynamics (arterial pressure, capillary pressure, and arterial and venous resistance), fluid filtration, and airway reactivity were monitored for 60 min in recirculating Ringer's-perfused, actively sensitized lungs. Bolus ovalbumin (30 micrograms) injection into the pulmonary artery produced initial (3 min postovalbumin) increases in pulmonary arterial pressure of 68 +/- 9% above baseline, which were followed by secondary increases (143 +/- 45% above baseline) at 30 min postovalbumin. Ovalbumin challenge also caused initial increases in pulmonary capillary pressure, arterial resistance, and venous resistance within 3 min after administration (100 +/- 34%, 51 +/- 10%, and 221 +/- 77% above baseline, respectively), which were further elevated at the end of the 60-min experimental period (292 +/- 74%, 66 +/- 29%, and 559 +/- 61% above baseline, respectively). Ovalbumin-induced increases in intratracheal pressure (771 +/- 142% above baseline) peaked at 3 min postchallenge and gradually returned towards baseline. Ovalbumin-induced changes in lung weight increased gradually over the perfusion period (3.5 +/- 1.0 g above baseline at 60 min postovalbumin). Antigen-induced changes in pulmonary arterial pressure, intratracheal pressure, and lung weight were abolished by pretreatment with the histamine1-receptor antagonist, pyrilamine (1 microM). The cyclooxygenase inhibitor, indomethacin (1 microM), potentiated antigen-induced secondary increases in pulmonary arterial pressure, intratracheal pressure, and lung weight.(ABSTRACT TRUNCATED AT 250 WORDS)