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Role of neurokinin‐A in recurrent airway obstruction

Airway hyper‐reactivity (AH) is the hall mark of recurrent airway obstruction (RAO) in horses. Of several inflammatory mediators responsible for AH, neurokinin‐A (NKA) has played a role in human and guinea pig AH. NKA causes severe bronchoconstriction by binding to neurokinin‐2 (NK‐2) receptors. Since the effects of NKA have not been examined in horses, the objectives of the study were to compare the in vitro responses of bronchial rings of healthy and RAO‐affected horses to NKA; and to determine and compare the expressions of NK‐2 receptors in the lungs between the groups. Bronchial rings, 4 mm wide, from each group were mounted in organ baths and attached to force transducers interfaced with a polygraph. Cumulative concentration‐response relationships to graded concentrations of NK‐A (10−7 M to 10−4 M) were determined. The expression of protein receptors was determined by Western blot and was compared by desitometric analysis. The results showed that NKA caused significantly greater contraction in RAO‐affected horses than those of healthy horses. The expression of the NK‐2 receptor protein was greater in RAO than the healthy horses. These findings indicate NKA plays an important role through NK‐2 receptors in the increased AH seen RAO horses.