Role of tachykinin NK2-receptor activation in the allergen-induced late asthmatic reaction, airway hyperreactivity and airway inflammatory cell influx in conscious, unrestrained guinea-pigs

Abstract

1. In a guinea-pig model of allergic asthma, we investigated the involvement of the tachykinin NK2 receptors in allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions and inflammatory cell influx in the airways, using the selective non-peptide NK2 receptor antagonist SR48968. 2. On two different occasions, separated by a 1 week interval, ovalbumin (OA)-sensitized guinea-pigs inhaled either vehicle (3 min) or SR48968 (100 nM, 3 min) at 30 min before as well as at 5.5 h after OA provocation (between the EAR and LAR) in a random crossover design. 3. SR48968 had no significant effect on the EAR, but significantly attenuated the LAR by 44.2+/-16.4% (P<0.05) compared to saline control. 4. The NK2 receptor antagonist did not affect the OA-induced AHR to histamine after the EAR at 5 h after OA challenge (3.59+/-0.59 fold increase in histamine reactivity vs 3.79+/-0.61 fold increase in the controls, NS), but significantly reduced the AHR after the LAR at 23 h after OA challenge (1.59+/-0.24 fold increase vs 1.93+/-0.15 fold increase, respectively, P<0.05). 5. Bronchoalveolar lavage studies performed at 25 h after the second OA provocation showed that SR48968 significantly inhibited the allergen-induced infiltration of neutrophils (P<0.05) and lymphocytes (P<0.01) in the airways. 6. These results indicate that NK2 receptor activation is importantly involved in the development of the allergen-induced late (but not early) asthmatic reaction and late (but not early) AHR to histamine, and that NK2 receptor-mediated infiltration of neutrophils and lymphocytes in the airways may contribute to these effects.

Figure 1

Effect of inhalations (3 min) of the selective NK₂ receptor antagonist SR48968 on the vagally-induced eNANC bronchoconstriction in OA-sensitized guinea-pigs. A nerve stimulation-response curve was performed before (control) and 30 min after inhalation of various concentrations of SR48968. Data represent mean values±s.e.mean of six animals. Statistical analysis by two-way repeated measures ANOVA followed by a Newman-Keuls test, ^*P<0.05, ^***P<0.001.

Figure 2

Effect of inhalations (3 min) of vehicle and the selective NK₂ receptor antagonist SR48968 (100 nM) on basal airway reactivity to histamine. Two subsequent histamine PC₁₀₀-measurements were performed 30 min before and 30 min after vehicle or SR48968 inhalation. Data represent mean values±s.e.mean of 7–9 animals. No statistical differences were found between groups (one-way ANOVA).

Figure 3

Effects of inhalations of the selective NK₂ receptor antagonist SR48968 (100 nM, 3 min) (A) and vehicle (B) on ovalbumin (OA)-induced airway hyperreactivity to histamine after the allergen-induced early (EAR) and late (LAR) asthmatic reactions. (A) Vehicle (control) or SR48968 were inhaled at 30 min before and 5.5 h after OA provocation on two subsequent occasions with 1 week interval. (B) Vehicle was inhaled at 30 min before and 5.5 h after OA provocation in both week 1 and week 2. Data represent mean values±s.e.mean of 7–9 animals. Statistical analysis by one-way ANOVA followed by a Newman-Keuls test: ^*P<0.05, ^**P<0.01.

Figure 4

Bronchoalveolar lavage cell counts at 25 h after inhalation of saline (control) or ovalbumin (OA). The OA-challenged animals received vehicle (3 min) at 30 min before and 5.5 h after OA challenge in week 1, and either vehicle (3 min) or SR48968 (100 nM, 3 min) at 30 min and 5.5 h after OA challenge in week 2. (A) Effects on total cells, eosinophils and macrophages; (B) Effects on lymphocytes, neutrophils and epithelial cells. Data represent mean values±s.e.mean of 5–7 animals. Statistical analysis by Kruskal-Wallis one way ANOVA, followed by a Mann-Whitney U-test: ^*P<0.05, ^**P<0.01, †P=0.10.