COMPARATIVE AIRWAY RESPONSE TO INHALED BRADYKININ, KALLIDIN, AND [DES-ARG9]BRADYKININ IN NORMAL AND ASTHMATIC SUBJECTS

Bradykinin, kallidin (lys-bradykinin), and [des-Arg9] bradykinin are oligopeptides that may contribute as mediators in the pathogenesis of asthma by interacting with specific receptors designated B1 and B2. In this study, we have investigated the airway response to inhaled bradykinin, kallidin, and [des-Arg9]bradykinin in normal and asthmatic subjects. Changes in airway caliber were followed as maximum expiratory flow at 30% of the vital capacity (Vp30) and as forced expiratory volume in 1 s (FEV1). Only one of the six normal subjects responded to bradykinin at the maximum cumulative concentration (5.33 mg/ml). Neither kallidin nor [des-Arg9]bradykinin had any measurable bronchoconstrictor effect in the normal subjects whether airway caliber was measured as Vp30 or FEV1. In the 10 subjects with asthma, bradykinin and kallidin, but not [des-Arg9]bradykinin, produced a concentration-related fall in FEV1. The geometric mean provocation concentrations of inhaled agonist reducing FEV1 by 20% of baseline were 0.03, 0.08, and 0.44 mg/ml for bradykinin, kallidin, and histamine, respectively. Bronchoconstriction produced by bradykinin and kallidin was maximal within 3 to 5 min with recovery occurring over 30 to 45 min. Because bradykinin and kallidin are agonists of B2 receptors and [des-Arg9]bradykinin is an agonist for B1 receptors, these in vivo structure activity studies suggest that asthmatic, but not normal, airways are hyperresponsive to kinins when compared to histamine and that this potent bronchoconstrictor action is a specific pharmacologic effect compatible with the stimulation of B2 receptors or a variant of these.