Characterization of adenosine receptors involved in adenosine-induced bronchoconstriction in allergic rabbits

1 Recent work has suggested that adenosine may be involved in asthma via the activation of A(1) receptors. However, the role of the recently cloned A(3) receptor in airways is largely unknown. In the present study, we have investigated the role of the A(3) receptor in adenosine-induced bronchoconstriction in allergic rabbits. 2 Aerosol challenge of antigen (Ag) immunized rabbits with the adenosine precursor, adenosine 5'-monophosphate (AMP), resulted in a dose-dependent fall in dynamic compliance (C-dyn) The maximum fall in C-dyn in these rabbits was significantly greater than that in litter matched, sham immunized animals (P<0.05). However, there was no significant difference in the maximum increase in airways resistance (R(L)) between Ag and sham immunized rabbits (P>0.05). 3 Aerosol challenge of Ag immunized rabbits with cyclopentyl-adenosine (CPA) (A(1)-receptor agonist) elicited a dose-dependent fall in C-dyn ill Ag immunized rabbits and the maximum fall in C-dyn in these rabbits was significantly greater than that observed in sham immunized rabbits (P<0.05). Similarly, CPA induced dose-dependent increases in R(L) in Ag immunized rabbits whereas sham immunized rabbits failed to respond to CPA within the same dose range. The maximum increase in R(L) in Ag immunized rabbits was significantly greater than that of sham immunized rabbits (P<0.05). 4 Aerosol challenge of either Ag or sham immunized rabbits with the A(3) agonist aminophenylethyladenosine (APNEA) did not elicit dose-dependent changes in either R(L) or C-dyn Moreover, there was no significant difference in the maximum response, measured by either parameter, between the two animal groups (P>0.05). 5 These data provide further evidence for a role of the A(1) receptor in the airways, but do not support a role for the Ag receptor in adenosine-induced bronchoconstriction in the allergic rabbit.