Neurokinin A‐LI release after antigen challenge in guinea‐pig bronchial tubes: influence of histamine and bradykinin

1 Our aim was to determine if antigen challenge stimulates sensory nerves and provokes the release of tachykinins. The involvement of histamine and bradykinin was studied by using specific receptor antagonists. Capsaicin‐induced responses were also examined. Experiments were performed in vitro on tracheal and bronchial preparations from ovalbumin‐sensitized guinea‐pigs. 2 Characterization of ovalbumin‐induced contraction, with regard to histamine and bradykinin, was carried out on airway ring preparations in the presence of phosphoramidon. The histamine H 1 receptor antagonist pyrilamine reduced allergen‐induced bronchial contractions by about 30%, whereas the bradykinin B 2 receptor antagonist icatibant (Hoe 140) did not significantly affect the response. Combined treatment with pyrilamine (1 μ M ) and icatibant (0.1 μ M ) reduced the contractions by about 80%, indicating a synergistic inhibitory action. Tracheal preparations were not significantly affected by treatments, neither were capsaicin‐induced contractions. 3 To study the outflow of tachykinins, we used a perfused bronchial‐tube preparation, allowing simultaneous measurement of smooth muscle tension and mediator release. Neurokinin A‐like immunoreactivity (NKA‐LI) and substance P‐like immunoreactivity (SP‐LI) were determined by radioimmunoassay. 4 The results of the perfusion study showed an increased outflow of NKA‐LI into the perfusate in response to ovalbumin (127% of basal) challenge. SP‐LI determined in some of the samples showed a much lower amount (40 to 70 times lower) of SP‐LI than NKA‐LI. Treatment with icatibant and pyrilamine, separately and in combination, significantly reduced the ovalbumin‐induced NKA‐LI outflow by 38%, 26% and 22%, respectively. 5 Capsaicin‐induced outflow (124% of basal) was not significantly affected by treatments (icatibant 121%, pyrilamine 107% and combined treatment 111% of basal). However, when pyrilamine was present the increased outflow was not statistically significant. 6 In conclusion, we found that allergen provocation of guinea‐pig bronchi caused an increased outflow of NKA‐LI that was reduced by treatment with both pyrilamine and icatibant. These findings demonstrate that the allergen‐induced release of histamine and bradykinin stimulate sensory nerves and thereby increase outflow of tachykinins that contribute to the allergic reaction.British Journal of Pharmacology (1997) 122 , 417–422; doi: 10.1038/sj.bjp.0701382