Enhancement of coronary vasodilator action of adenosine triphosphate by dipyridamole.

It has been reported that previously administered dipyridamole intensifies the coronary vasodilator action of adenosine compounds. In the present study, a combination of dipyridamole and ATP at doses that alone are ineffective was examined for its effect on the coronary sinus blood flow. In 10 anesthetized dogs, heart rate, arterial blood pressure, cardiac output, and coronary sinus blood flow were measured before and during a 20-min constant-rate infusion of (a) ATP alone, 1 mg/min; (b) a combination of ATP, 1 mg/min, and dipyridamole, 0.005 mg/kg/min; and (c) dipyridamole alone, 0.005 mg/kg/ min. Coronary sinus flow was measured by a newly developed thermodilution flowmeter. Consistently during the infusion of ATP or dipyridamole alone no changes in the measured parameters occurred, whereas during infusion of the combination a very marked and sustained elevation (+493$) of coronary flow occurred, associated with a moderate increase in cardiac rate (+37$) and output (+42$) and a decrease in arterial blood pressure (—17$). In 7 other dogs, coronary vasodilator responses to ATP were determined before and 1 hour after a single 10-mg dose of dipyridamole. After dipyridamole, the coronary vasodilator action of ATP increased 5to 100-fold. In a third group of 3 dogs, dipyridamole did not enhance the coronary vasodilator effects of nitroglycerin, bradykinin, or acetylcholine. ADDITIONAL