Cholinergic Mechanisms in the Sinus Node

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Abstract
Acetylcholine is directly perfused into the canine sinus node in vivo through its cannulated nutrient artery. After atropinization, the chronotropic action from intranodal administration of acetylcholine was identical to that of control injections of Ringer's solution alone. Eserine produced only a negative chronotropic action before, and no significant action after, atropinization. Direct perfusion of the sinus node with hemicholinium (1 mg/ml) completely blocked the response to vagal stimulation but had no effect on the response to stimulation of the stellate ganglion. The evidence is interpreted as indicating that acetylcholine has only a negative chronotropic action in the canine sinus node and that it neither releases significant amounts of local nodal norepinephrine nor is necessary to the normal response of the sinus node to stellate ganglion stimulation.

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