Flow and pressure responses of coronary arteries and veins to vasodilating agents

The response to a bolus injection of nitroglycerine, adenosine, nifedipine, and dipyridamole of the canine systemic as well as coronary artery and venous circulations was observed and contrasted. Particular attention was paid to the time of change of pressures and flows and to changes in oxygen extraction by the myocardium induced by the pharmacological agents. The dosages of vasodilators used were selected so that no significant change in aortic blood flow occurred. Nitroglycerine and adenosine caused a rapid and similar vasodilation in the coronary circulation. Oxygen extraction was not altered by nitroglycerine, but was decreased by adenosine. The onset time of the vasodilation produced by either nifedipine or dipyridamole was similar, but the time to peak action was much slower for dipyridamole. As well, the effect of dipyridamole on intramyocardial and left intraventricular pressures was more delayed than that following the injection of the other agents. Oxygen extraction was reduced by nifedipine and dipyridamole. These results indicate that pharmacological vasodilating agents can affect coronary arteries, coronary veins, and myocardial oxygen extraction differently.