Comparison of the potency of 8−phenyltheophylline as an antagonist at A1 and A2 adenosine receptors in atria and aorta from the guinea-pig

Abstract

Abstract The potency of 8−phenyltheophylline as an antagonist at A, adenosine receptors in guinea-pig atria and at A2 adenosine receptors in the guinea-pig aorta has been investigated. 8-Phenyltheophylfine was an apparently competitive antagonist of the negative chronotropic effect of adenosine, 2-chloroadenosine, L- N6 -phenyl-isopropyl adenosine (L-PIA) and 5′- N-ethylcarboxamide adenosine (NECA) on atria and of the relaxant effect of adenosine, 2−chloroadenosine and NECA on the aorta. The pA2 values for 8−phenyltheophylline ranged from 6.4 to 6.6 and were not significantly different, irrespective of the agonist or tissue used. These results indicate that 8−phenyltheophylline is a relatively potent antagonist at adenosine receptors but does not exhibit selectivity for either of the putative sub-types in isolated tissues.