EFFECTS OF INOSINE ON ADENOSINE-INDUCED CORONARY VASODILATION IN THE OPEN-CHEST DOG

The effects of inosine (CAS 58-63-9) on adenosine-induced coronary vas odilation were studied in open-chest dogs. Inosine and hypoxanthine we re infused into the coronary artery at a rate to obtain respective cal culated coronary plasma concentrations of 10(-5) mol/l, and the dose-c oronary flow response of adenosine was recorded with and without inosi ne or hypoxanthine infusion. When the maximum coronary dilation was ob tained, 10 ml of 2 x 10(-3) mol/l 8-phenyltheophylline (8-PT) solution was injected into the femoral vein. Additionally, adenosine deaminase activity was measured in vitro in the presence of various concentrati ons of either inosine or hypoxanthine. It was found that inosine, but not hypoxanthine, intensified the coronary vasodilatory effect of aden osine, which was abolished by 8-PT injection: EC50 of adenosine was re duced from 10(-5.43) mol/l to 10(-5.90) mol/l by inosine. Inosine and hypoxanthine did not affect adenosine deaminase activity at concentrat ions of 10(-4) mol/l or less. These findings indicate that inosine int ensifies the coronary vasoactivity of adenosine, independent of inhibi tion of adenosine deaminase activity.