Adenosine receptors: promising targets for the development of novel therapeutics and diagnostics for asthma.

Interest in the role of adenosine in asthma has escalated considerably since the early observation of its powerful bronchoconstrictor effects in asthmatic but not normal airways. A growing body of evidence has emerged in support of a proinflammatory and immunomodulatory role for the purine nucleoside adenosine in the pathogenic mechanisms of chronic inflammatory disorders of the airways such as asthma. The fact that adenosine enhances mast cell allergen-dependent activation, that elevated levels of adenosine are present in chronically inflamed airways, and that adenosine given by inhalation cause dose-dependent bronchoconstriction in subjects with asthma emphasizes the importance of adenosine in the initiation, persistence and progression of these common inflammatory disorders of the airways. These distinctive features of adenosine have been recently exploited in the clinical and research setting to identify innovative diagnostic applications for asthma. In addition, because adenosine exerts its multiple biological activities by interacting with four adenosine receptor subtypes, selective activation or blockade of these receptors may lead to the development of novel therapies for asthma.