Effect of adenosine on the relaxation of coronary arteries at varying pH values.

The efficiency of adenosine to relax the bovine coronary arterial strips increased significantly by lowering the bath pH from 7.4 to 6.8 (CO2 or HCO-3). The large vessels (3-4 mm O.D.) relaxed with greater significance at higher concentrations of adenosine, whereas small vessels (0.5-0.7 mm O.D.) relaxed better at low concentrations of adenosine. Theophylline and 8-phenyltheophylline competitively inhibited the effect of adenosine. 8-phenyltheophylline was found to be a better antagonist than theophylline. Furthermore, binding assays with 2-3H adenosine displayed a single species of binding sites. The Kd was 3 X 10(-6) M and 4 X 10(-6) M, while Bmax was 48 and 19 pmoles/mg protein for small and large vessels, respectively. The antagonistic effect of theophylline and 8-phenyltheophylline was not affected by pH variations. It is concluded that relaxation of coronary arteries by adenosine is affected by pH variations.