Preferential Distribution of Inhibitory Cardiac Receptors with Vagal Afferents to the Inferoposterior Wall of the Left Ventricle Activated during Coronary Occlusion in the Dog

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The purpose of this study was to determine the relative magnitudes of the reflex effects mediated by cardiac receptors during anterior as opposed to inferoposterior ischemia of the left ventricle of the dog. Cessation of perfusion (coronary ‘occlusion’) of the circumflex coronary artery (Cx) in 29 chloralose-anesthetized dogs with common carotids ligated (group I) resulted in significant bradycardia and hypotension, but in no significant change in perfusion pressure in the gracilis muscle perfused at constant flow. Occlusion of the left anterior descending coronary artery (LAD) produced less hypotension, no change in heart rate, and vasoconstriction in the gracilis. After vagotomy and aortic nerve section, no significant change in heart rate or gracilis perfusion pressure was observed during LAD or Cx occlusion, and the blood pressure responses to LAD and Cx occlusion were not different. In nine dogs with sinoaortic denervation (group II), brief Cx occlusion resulted in bradycardia, hypotension, and vasodilation in the gracilis muscle. LAD occlusion in group II dogs caused less hypotension and no change in heart rate or gracilis perfusion pressure. After vagotomy, the bradycardia and vasodilation resulting from Cx occlusion were abolished and the blood pressure responses to LAD and Cx occlusion were not different. The weights of left ventricle perfused by each occluded vessel were not different. These data show that left ventricular receptors with vagal afferents which are activated during coronary occlusion and which mediate cardioinhibitory and vasodepressor responses are located mainly in the inferoposterior left ventricle of the dog heart.

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