Exercise tachycardia not due to blood-borne agents in canine cardiac denervation

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Abstract
Ten dogs with chronic cardiac denervation were exercised (5.5 km/hr, 21% grade) before and after treatment with the beta adrenergic blocking drug propranolol. Cardiac acceleration (mean, 34 beats/min) persisted after adrenergic blockade. Chemical blockade of the cardiac autonomic system was effected by atropine and propranolol in normal dogs. The cardiac acceleration during exercise after chemical blockade was similar to that seen in dogs with surgical denervation of the heart. Six dogs with cardiac denervation were studied during continuous work of increasing severity before and after propranolol administration. The data indicated that circulating norepinephrine was required for the consistent performance of the most severe grade of work. Normal dogs and dogs with cardiac denervation served as blood donors to perfuse 17 normal and 6 chronically denervated isolated hearts (Langendorf technique) during exercise of the blood donor dog. The isolated hearts showed a tachycardia that was proportional to the work done by the donor dog and which was abolished by propranolol.