Hyperresponsiveness to adenosine in sensitized Wistar rats over-expressing A1 receptor

Airway hyperreactivity is characterized by increased responsiveness to bronchoconstrictor stimuli and it is hallmark of asthma. Adenosine is an ubiquitous signaling nucleoside resulting from ATP catabolism, whose extracellular levels increase following cellular damage or stress. Adenosine plays a role in asthma; asthmatics, but not normal subjects, present bronchoconstriction following inhalation of adenosine or of its precursor, adenosine-5′-monophosphate, most likely via adenosine A2B receptor on mast cells. However, the mechanism underling the increased airway smooth muscle sensitivity to adenosine in asthmatics remains to be elucidated. Early experimental studies suggested the involvement of A1 receptor; this hypothesis has been confirmed by more recent studies on guinea pigs and is corroborated by the finding of an increased adenosine A1 expression on asthmatic bronchial tissues. Brown Norway rats, the strain usually used to assess asthma models, develop hyperresponsiveness to adenosine 3 h following allergen challenge, but not 24 h thereafter, without involvement of A1 receptor. Here, we investigated the role of adenosine A1 receptor in sensitized Wistar rats showing airway hyperresponsiveness 24 h following allergen challenge. We found that on bronchi of sensitized Wistar rats challenged with allergen there is an increased adenosine A1 receptor expression on smooth muscle that is responsible for hyperresponsiveness to adenosine and ovalbumin.