The effects of dipyridamole on the myocardial vasodilator actions of noradrenaline, isoprenaline and adenosine.

1. In anaesthetized cats, intravenous adenosine infusions decreased resistance to blood flow in the myocardial vascular bed. This effect of adenosine was augmented during the 60 min following the intravenous injection of dipyridamole (1 mg/kg).2. In different experiments, intravenous infusions of noradrenaline caused either a slight increase or a slight decrease in myocardial vascular resistance. The dilator component of the action of noradrenaline was not augmented by dipyridamole.3. Isoprenaline infusions decreased the resistance of the myocardial bed. This effect was unaltered after dipyridamole.4. These results do not support the hypothesis that part of the effect of catecholamines on myocardial vascular resistance involves the release of adenosine from hypoxic myocardial cells.