THE EFFECTS OF DIPYRIDAMOLE AND NITROGLYCERIN ON CORONARY BLOOD FLOW, MEAN ARTERIAL PRESSURE, AND HEART RATE IN DOGS

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Abstract
The effects of the coronary dilators dipyridamole and nitroglycerin were studied in 21 dogs, either under conditions of constant pulmonary artery inflow (constant PAI experiments) or under conditions of constant arterial pressure as well (constant PAI and AP experiments). The two drugs had different effects on coronary flow in the constant PAI experiments, although both reduced peripheral arterial pressure. Nitroglycerin caused a brief biphasic response, consisting of a peak increase followed by a fall below control, whereas dipyridamole maintained coronary flow above control levels and for a much longer period.In the constant PAI and AP experiments, the biphasic response after nitroglycerin was not observed, and a significant increase in the peak flow over that noted in the constant PAI experiments occurred. With dipyridamole the peak coronary flow was not significantly changed by holding the arterial pressure constant.The implication from the significantly greater coronary flow response after nitroglycerin in the constant PAI and AP experiments compared with that in the constant PAI experiments is that in the latter experiments reduced coronary resistance secondary to nitroglycerin would seem to have been masked by the rapid fall in peripheral pressure. Dipyridamole caused a progressive increase in coronary flow in the face of a reduction in peripheral pressure.

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