Adenosine enhances antigen-induced bronchoconstriction and histamine release in rat isolated lungs

The effects of adenosine and some of its analogues on bronchoconstriction and mediator release were studied in isolated lungs of actively sensitized rats. Adenosine (ADO) and its analogues R-phenyl-iso-propyl-adenosine (R-PIA) and N-ethyl-carboxamide-adenosine (NECA), enhanced antigen-induced bronchoconstriction in a dose-dependent manner. The enhancement of anaphylactic bronchoconstriction by adenosine and its analogues was accompanied by a rise in histamine release. The observed rank order of potency for adenosine and analogues (NECA greater than or equal to R-PIA greater than ADO) did not permit an unequivocal classification of the adenosine receptor involved. Dipyridamole and S-(p-nitrobenzyl-6-thioinosine) (NBTI), both inhibitors of adenosine uptake, had no inhibitory influence on the adenosine-induced enhancement of anaphylactic bronchoconstriction. Therefore, this enhancement was likely to be mediated through an extra-cellular receptor. Theophylline inhibited the enhancement of anaphylactic bronchoconstriction by adenosine in a concentration-dependent manner, without affecting preformed mediator release.