Are the anti-allergic actions of theophylline due to antagonism at the adenosine receptor

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Abstract
Adenosine potentiated anaphylactic histamine release from isolated rat mast cells in a dose-dependent manner between 10−8 and 10−5 M. Adenosine was found to be present during a normal incubation of mast cells, but the concentration was low (2×10−8 M). In rat plasma the concentration was 1.5×10−7 M. The effect of 10−5 M adenosine was dose-dependently inhibited by theophylline. 50% inhibition was found at 3×10−5 M theophylline. Cyclic nucleotide phosphodiesterase inhibition required much higher concentrations (IC50∼10−3 M). It is suggested that some of the anti-allergic actions of theophylline (clinical concentration range: 10−5–10−4 M) does not involve cyclic nucleotides but may be due to inhibition of the effects of endogenous adenosine.