Vasomotor Responses to Acute Coronary Occlusion in the Dog

Abstract

The acute circulatory effects of ligation of the anterior descending branch of the left coronary artery were studied in 26 anesthetized dogs. Changes in vasomotor tone were assayed by comparing pressure-flow relationships in a hind leg during control and exptl. periods. A simple exponential relationship was observed between control pressure and flow in the majority of expts. In approx. 1/4 of the expts. no significant change in vasomotor tone was observed, and yet blood pressure returned to or toward control following occlusion. In these cases, compensation must have been largely cardiac in origin. In most of the remaining expts. a significant degree of vasocon-striction occurred following production of myocardial ischemia, or ventricular fibrillation developed before the vasomotor response could be ascertained. In not a single case did an appreciable degree of vasodilatation appear, nor did mean arterial pressure ever return toward control levels following bilateral vagotomy. Therefore, the decline in blood pressure resulting from acute coronary occlusion in these expts. was not due to any reflex mechanism originating in ischemic myocardial tissue. The only possible physiol. counterpart of the veratrinic reflex observed in our expts. was the decrease in heart rate obtained in two experiments following coronary ligation. The fact that this relative bradycardia was abolished by vagal section is compatible with this possibility, but the afferent limb of this reflex could not be established.