Separation of cardioaccelerator and coronary vasomotor fibers in the dog

In the dog the preganglionic ‘B’ fibers in the accelerator nerve that synapse with intracardiac adrenergic or cholinergic neurons are the vasomotor fibers of the coronaries. Stimulation of the coronary constrictors produces a reduction of flow, but the O 2 consumption of the heart does not change. The A-V O 2 difference and the A-V lactate difference increase proportionately indicating that no change takes place in the metabolic pattern. Stimulation of the postganglionic cardioaccelerator fibers increases blood pressure, coronary flow and O 2 consumption, the A-V lactate difference increases or decreases. The metabolic pattern is also altered. A true vasomotor dilatation (no change in the metabolic pattern) can also be induced in the dog. These fibers are cholinergic in nature. The vagus plays no role in the innervation of the coronaries in the dog.