Phosphodiesterase inhibitors reduce bronchial hyperreactivity and airway inflammation in unrestrained guinea pigs.

A new guinea pig model of allergic asthma was used to investigate the effects of low doses of the phosphodiesterase inhibitors, rolipram (phosphodiesterase IV selective), ORG 20241 (N-hydroxy-4-(3,4-dimethoxyphenyl)-thiazole-2-carboximidamide; dual phosphodiesterase III/IV inhibitor with some selectivity for the phosphodiesterase IV isoenzyme), and of theophylline (non-selective) on allergen-induced early and late phase asthmatic reactions, bronchial hyperreactivity to histamine inhalation, and airway inflammation. Theophylline (25 mg/kg i.p.) and ORG 20241 (5 mg/kg i.p.) did not affect histamine-induced bronchoconstriction, whereas rolipram (75 micrograms/kg i.p.) only slightly reduced the response to histamine at 7 h after administration. However, bronchial hyperreactivity after the early and after the late reaction was significantly reduced by theophylline, rolipram and ORG 20241, while bronchoalveolar lavage studies revealed a selective inhibition of airway inflammation by the phosphodiesterase inhibitors. Theophylline significantly reduced the number of eosinophils, neutrophils and macrophages; rolipram reduced the number of neutrophils and lymphocytes, and ORG 20241, the number of eosinophils and macrophages. None of the compounds at the dosage indicated reduced the early and late reaction when administered i.p. 1 h before allergen exposure to defined dual responding animals. These results indicate that non-bronchodilator doses of these phosphodiesterase inhibitors markedly reduce the allergen-induced development of bronchial hyperreactivity as well as airway inflammation, presumably by selectively inhibiting cellular migration. The results suggest that an orchestrated series of cellular interactions is involved in the development of bronchial hyperreactivity. It is concluded that phosphodiesterase inhibitors may be very useful in the treatment of bronchial asthma.

Contribution of a cholinergic reflex mechanism to allergen-induced bronchial hyperreactivity in permanently instrumented, unrestrained guinea-pigs.

1. In conscious, permanently instrumented, unrestrained, ovalbumin-sensitized guinea-pigs the development of allergen-induced bronchial hyperreactivity to histamine- and methacholine-inhalation was investigated after the early as well as after the late asthmatic response. 2. The allergen-induced increase in bronchial reactivity to histamine was significantly higher than to methacholine. 3. The muscarinic receptor antagonist, ipratropium bromide (1.0 mM, 3 min inhalation), blocked methacholine-induced bronchoconstriction and caused a significant 1.7 fold inhibition of the histamine-induced bronchoconstriction of control animals. 4. A lower dose of ipratropium bromide (0.1 mM, 3 min inhalation) had no significant effect on histamine-induced bronchoconstriction in control animals, but significantly reduced the allergen-induced increase in bronchial reactivity to histamine between the early and late asthmatic response. At 1.0 mM ipratropium bromide, no further reduction was observed. 5. These results clearly indicate that an exaggerated cholinergic reflex mechanism contributes to allergen-induced bronchial hyperreactivity to histamine.

Influence of sensitization and allergen provocation procedures on the development of allergen-induced bronchial hyperreactivity in conscious, unrestrained guinea-pigs.

The effects of different sensitization and allergen provocation regimens on the development of allergen-induced bronchial hyperreactivity (BHR) to histamine were investigated in conscious, unrestrained guinea-pigs. Similar early and late phase asthmatic reactions, BHR for inhaled histamine after the early (6 h) as well as after the late reaction (24 h), and airway inflammation were observed after a single allergen provocation in animals sensitized to produce mainly IgG or IgE antibodies, respectively. Repeating the allergen provocation in the IgE-sensitized animals after 7 days, using identical provocation conditions, resulted in a similar development of BHR to histamine inhalation. Repetition of the allergen provocation during 4 subsequent days resulted in a decreased development of BHR after each provocation, despite a significant increase in the allergen provocation dose necessary to obtain similar airway obstruction. The number of inflammatory cells in the bronchoalveolar lavage was not significantly changed after repeated provocation, when compared with a single allergen provocation. Finally, we investigated allergen-induced bronchial hyperreactivity by repetition of the sensitization procedure at day 7 and 14 (booster), followed by repeated allergen provocation twice a week for 5 weeks. Surprisingly, no BHR to histamine could be observed after either provocation, while the number of inflammatory cells in the bronchoalveolar lavage fluid after 5 weeks was enhanced compared with controls. These data indicate that both IgE and IgG sensitized guinea-pigs may develop bronchial hyperreactivity after a single allergen provocation. Repeated allergen exposure of IgE sensitized animals causes a gradual fading of the induced hyperreactivity despite the on-going presence of inflammatory cells in the airways, indicating a mechanism of reduced cellular activation.

Relationships among allergen-induced early and late phase airway obstructions, bronchial hyperreactivity, and inflammation in conscious, unrestrained guinea pigs.

The relationship among allergen-induced early asthmatic reactions (EARs) and late asthmatic reactions (LARs), early (between EAR and LAR) and late (after LAR) changes in bronchial reactivity to histamine and infiltration of inflammatory cells into the airways were investigated with a new model of chronically instrumented, unrestrained, and ovalbumin-sensitized guinea pigs. Two different provocation strategies were examined. With the use of stepwise increasing allergen concentrations, all 21 animals responded with an EAR, which in 15 animals (71%) was followed by an LAR. By inhalation of a single allergen concentration for up to 15 minutes, 11 of 14 animals showed an EAR, which in 10 animals (71%) was followed by an LAR. One animal did not respond, whereas the remaining two showed only an LAR. At 6 hours (after the EAR) and 24 hours (after the LAR) after allergen provocation, a significant bronchial hyperreactivity (BHR) toward histamine aerosol was observed in the dual responding animals (both protocols), but not significant changes were observed in animals with a single EAR or a single LAR. Significant correlations were found between the initial increase in airway obstruction after allergen provocation and the severity of the EAR and LAR, as well as the early and late BHR; in addition, a significant correlation was found between the early and late BHR. In contrast, the severity of the LAR did not correlate with the BHR at 6 hours and 24 hours. At 6 hours, there was a marked tendency to an increase in the number of eosinophils and a significant increase in the number of neutrophils in the bronchoalveolar lavage. At 24 hours after provocation, the number of eosinophils and neutrophils was significantly enhanced. These data suggest that early activation of mast cells and/or inflammatory leukocytes may determine the development of the LAR, as well as the early and late BHR, although there appears to be no causal relationship between the BHR at both time points and the severity of the LAR. The relationships among allergen-induced EAR and LAR, early and late BHR, and airway inflammation observed in this new guinea pig model are strikingly similar to those observed in patients with asthma.

Dissociation between bronchial hyperreactivity in vivo and reduced beta-adrenoceptor sensitivity in vitro in allergen-challenged guinea pigs.

In a recently developed guinea pig model of allergic asthma, we investigated the relationships between allergen-induced bronchial hyperreactivity in vivo, tracheal smooth muscle function in vitro, and the number of inflammatory cells in the bronchoalveolar lavage. At 6 h after allergen provocation (after the early asthmatic reaction) bronchial hyperreactivity to histamine aerosol was observed, which was still present, but reduced, at 24 h after the challenge (after the late asthmatic reaction). The severity of bronchial hyperreactivity at 6 h and at 24 h after each of four daily allergen provocations was progressively reduced. The contractile properties of tracheal smooth muscle preparations in response to methacholine or histamine were not changed at 6 h and 24 h after a single allergen provocation, as well as at 24 h after the fourth of the repeated provocations. However, the sensitivity to isoprenaline-induced relaxation of a half-maximal contraction obtained with methacholine or histamine was significantly reduced at 24 h after either a single or the fourth of the repeated provocations. The time course of the reduced beta-adrenoceptor sensitivity in vitro did not correlate with that of bronchial hyperreactivity in vivo. However, it was parallelled by a progressive infiltration of inflammatory cells in the airways, suggesting that mediators from these cells may decrease airway smooth muscle beta-adrenoceptor sensitivity.

Role of histamine in allergen-induced asthmatic reactions, bronchial hyperreactivity and inflammation in unrestrained guinea pigs.

In a new model using conscious, unrestrained and ovalbumin-sensitized guinea pigs, we investigated the effects of the selective histamine H1 receptor antagonist, mepyramine, on the development of allergen-induced early and late asthmatic reactions, bronchial hyperreactivity and airway inflammation, having each animal as its own control. In guinea pigs responding to a first allergen exposure with an early as well as a late asthmatic reaction (82% of the animals) a second, identical, allergen provocation was performed, in the absence (control) or presence of 1 mg/ml mepyramine aerosol, inhaled for 10 min, 1 h before provocation. The mepyramine treatment significantly reduced both early and late asthmatic reactions and prevented the development of bronchial hyperreactivity to histamine and methacholine after both reactions. Examination of the bronchoalveolar lavage fluid 24 h after the second allergen provocation revealed a general reduction of inflammatory cells after mepyramine treatment. The results indicate that histamine, released during the early asthmatic reaction, contributes to the development of the late asthmatic reaction as well as of early and late bronchial hyperreactivity, possibly via an effect on airway inflammation.