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

Summary 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 HCO₃^–). 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 K_d was 3×10^–6 M and 4×10^–6 M, while B_max 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.This work was supported by HL27339