Specific antagonism of adenosine‐induced bronchoconstriction in asthma by oral theophylline.

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Abstract
The airway response to increasing concentrations of inhaled adenosine and histamine after oral theophylline or matched placebo was studied in 9 asthmatic subjects. Changes in airway caliber were followed as sGaw [specific airways conductance] and FEV1 [forced expiratory volume in 1 s] and concentration-response curves constructed. Inhaled adenosine caused concentration-related bronchoconstriction and was 4-5 times less potent than inhaled histamine. Theophylline, which achieved a mean plasma level of 15.9 and 16.6 .mu.g/ml on the histamine and adenosine study days, respectively, caused significant increases in FEV1 (17%) and sGaw (41-53%) whereas placebo had no effect. Theophylline also protected the airways against histamine- and adenosine-induced bronchoconstriction. Theophylline had a greater protective effect against adenosine (concentration-ratio 17.4 for FEV1 and 12.8 for sGaw) than against histamine (concentration ratio 5.6 for FEV1 and 5.4 for sGaw (P < 0.05)). At therapeutic concentrations theophylline is a specific antagonist of the airway effects of adenosine in addition to being a bronchodilator and a functional antagonist.