Key result
Acetylcholine exerts purely negative chronotropic effects in canine sinus nodes without stimulating local norepinephrine release.
Why the study?
The specific cholinergic effects of acetylcholine on the canine sinus node and its role in vagal and stellate ganglion stimulation responses were unclear.
Answers are grounded in this paper and cite their sources.
Clarifies muscarinic mediation of vagal sinus node effects in canines; leaves open translation to human autonomic regulation.
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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Thomas N. James (1966) studied Canine sinus node physiology. Acetylcholine perfusion vs. Ringer's solution was evaluated on Chronotropic action. Direct perfusion of acetylcholine demonstrated only a negative chronotropic action in the canine sinus node in vivo, without releasing significant local nodal norepinephrine.
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