Evidence that allergen-induced contraction of guinea pig bronchi is mediated in part by the release of tachykinins.

Abstract

To study the role of tachykinins in allergic responses in the airways of guinea pigs sensitized to ovalbumin (OVA), we examined the bronchial contractile response to allergen in the presence or absence of the tachykinin antagonist FK224 in vitro. Because neutral endopeptidase (NEP) effectively cleaves tachykinins, we incubated bronchial tissues with the NEP inhibitor phosphoramidon (10(-5) M) to maintain the activity of endogenously released tachykinins. Then we added 10(-5)% (10 microns/ml) OVA in the presence or absence of FK224 (10(-5) M). FK224 significantly inhibited OVA-induced contraction plateaued and began to relax, we added 10(-5) M phosphoramidon. In the tissue without FK224, phosphoramidon blocked the relaxation and enhanced the contraction. In contrast, in the tissues treated with FK224, phosphoramidon did not enhance the OVA-induced contraction. The enhancement of the contraction induced by phosphoramidon was not inhibited by the sodium channel blocker tetrodotoxin. These results suggest that (1) allergic response causes release of tachykinin-like substances to induce bronchial contraction in part, (2) these responses are blocked by tachykinin antagonist FK224 and (3) nerve conduction is not necessary for the release of tachykinin-like substances induced by allergic response in the guinea pig bronchus.