The mechanisms responsible for the development of airway hyperresponsiveness in asthma are poorly understood. Adenosine levels are high in the lungs of patients with asthma, but a role for adenosine in the development of this cardinal feature of asthma has not been previously reported.

To determine the capacity of adenosine to induce airway hyperresponsiveness, and to investigate the mechanisms behind these effects of adenosine on airway physiology.

Wild-type C57BL/6 mice were exposed to aerosolized adenosine analog adenosine-5′ N-ethylcarboxamide (NECA), and subsequent hyperresponsiveness to methacholine was investigated by measuring airway mechanics after anesthesia and tracheostomy. Similar experiments were conducted with A₁-deficient, A₃-deficient, and mast cell–deficient mice, as well as with mast cell–deficient mice engrafted with wild-type (wt) or A₃^–/– mast cells. The effect of NECA on methacholine-induced tension development in ex vivo tracheal rings was also examined.

Exposure of wt mice to NECA resulted in the robust induction of airway hyperresponsiveness. NECA failed to induce hyperresponsiveness to methacholine in tracheal ring preps ex vivo, and NECA-induced airway hyperresponsiveness in vivo was not affected by the genetic inactivation of the A₁ adenosine receptor. In contrast, NECA-induced airway hyperresponsiveness was abolished in A₃ adenosine receptor-deficient mice and in mice deficient in mast cells. Reconstitution of mast cell–deficient mice with wt mast cells restored hyperresponsiveness, whereas reconstitution with A₃ receptor–deficient mast cells did not.

Adenosine induces airway hyperresponsiveness indirectly by activating A₃ receptors on mast cells.