INTER‐RELATIONS BETWEEN THE ACTIONS OF DIPYRIDAMOLE, ADENOSINE, AMINOPHYLLINE AND PROPRANOLOL ON THE CORONARY CIRCULATION OF THE TRANSPLANTED DOG HEART
Summary: To study the effects of certain vasodilator drugs on the coronary vasculature of the transplanted heart, dog hearts were Implanted into the necks of recipient dogs and connected to the circulation so that coronary blood flow and coronary vascular resistance could be measured continuously. During the first six hours close arterial injections of adenosine and dipyridamole produced marked increases in coronary blood flow and reduced coronary vascular resistance in the transplanted heart; dipyridamole greatly potentiated the vasodilator actions of adenosine. Propranolol, in a beta adrenergic blocking dose, did not alter coronary blood flow or coronary vascular resistance or influence the actions of dipyridamole or adenosine. Low dose infusions of aminophylline uniformly reduced coronary blood flow and increased coronary vascular resistance and also blocked the actions of dipyridamole and adenosine. The blocking effect was similar with higher doses of aminophylline which temporarily increased coronary blood flow. The findings show that coronary vascular reactivity to dipyridamole and adenosine is maintained up to at least six hours after transplantation, and suggest that dipyridamole acts largely through aderosine. Propranolol does not increase coronary vascular resistance in the denervated heart. The aminophylline‐mediated increase in coronary vascular resistance could result from a blocking of the vasodilator effects of adenosine locally produced in non‐ischaemic myocardium.