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

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 x 10(-8) M). In rat plasma the concentration was 1.5 x 10(-7) M. The effect of 10(-5) M adenosine was dose-dependently inhibited by theophylline. 50% inhibition was found at 3 x 10(-5) M theophylline. Cyclic nucleotide phosphodiesterase inhibition required much higher concentrations (IC50 approximately 10(-3) M). It is suggested that some of the anti-allergic actions of theophylline (clinical concentration range: 10(-5) M) does not involve cyclic nucleotides but may be due to inhibition of the effects of endogenous adenosine.