Characterization of adenosine receptors involved in adenosine-induced contraction in sensitized guinea pig isolated trachea

The adenosine receptor responsible for the bronchoconstriction seen in asthmatic patients is not yet known, moreover the physiological function and the role of the A3 receptor in adenosine induced bronchoconstriction has not established. In the present study, we investigated in ovalbumin sensitized guinea pig isolated trachea the role of the A3 receptor in mediating adenosine induced bronchoconstriction by using adenosine (ADO), N6- cyclopentyladenosine (CPA), a selective A1 adenosine receptor agonist, 2- chloro-N6(3-iodobenzyl)adenosine-5'-N-methyluronamide(CI-IB-MECA), a selective A3 receptor agonist and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective A1 adenosine receptor antagonist. Our data show that CPA concentration effect curves, in sensitized guinea pig isolated trachea, causes contraction of airway smooth muscle and a 30 min pretreatment with DPCPX shifted to the right these concentration effect curves. Moreover, in the same experimental conditions administration of CI-IB-MECA did not show responses. In view of the inability of CI-IB-MECA to elicit a response in our allergic guinea pig model in terms of airway constriction, and the ability of DPCPX to shift to the right the concentration effect curves of ADO and CPA, these data provide further evidence for a role of the A1 receptors in adenosine induced contraction of sensitized guinea pig isolated trachea but don't support a role for the A3 receptor.