Tachyphylaxis to repeated challenges with inhaled adenosine in asthmatic subjects.

Adenosine, when administered as an aerosol to asthmatic subjects, provokes a prompt dose-dependent bronchoconstriction. The aim of this study was to establish whether tachyphylaxis in response to repeated inhalations with adenosine occurs in asthmatic subjects. Eight asthmatic patients were studied on three separate days (days A, B, and C) at the same time of day for each subject. Three inhalation tests were performed, separated by one hour, on each study day. The study was conducted in a double-blind fashion and performed in random order. On day A, three adenosine inhalation tests were performed to assess adenosine tachyphylaxis. On day B, a saline inhalation test was carried out between two adenosine challenges to assess the time course of the adenosine tachyphylaxis. On day C, three methacholine inhalation tests were performed to confirm that tachyphylaxis does not occur to methacholine. Repeated inhalation with adenosine, but not methacholine, produced a progressive loss of responsiveness to the nucleoside, which was particularly manifest with the third challenge.