Source of intrinsic innervation of canine ventricles: a functional study

Recently it has been suggested that the parasympathetic innervation of the ventricles is by way of postganglionic axones that emanate from ganglion cells in the atria, reaching the ventricles by traversing the atrioventricular (AV) groove. We designed a series of experiments to test this hypothesis. Phenol (89%) was applied to the AV groove and surrounding 5 mm of epicardium in 21 dogs on cardiopulmonary bypass. The effects of intracoronary acetylcholine (ACh; 1-5 micrograms) and intracoronary nicotine (NIC; 25-100 micrograms) on cardiac isovolumic pressures were evaluated after beta-blockade. In another series of experiments, eight dogs were exposed to phenol in the same way and allowed to recover for 7-10 days. Atrial and ventricular responses to NIC were unaffected by phenol application to the AV groove in the acute animals when compared with application of saline alone. However, in the chronic animals, pretreatment with phenol 7-10 days previously reduced the ventricular responses to NIC by 70% while leaving the atrial responses intact. These data indicate that the intrinsic cardiac nerves (ICN) of the canine ventricles consist primarily of postganglionic parasympathetic axones which arise from supraventricular ganglia and cross the AV groove.