AUTONOMIC INTERACTIONS FOR CONTROL OF ATRIAL RATE ARE MAINTAINED AFTER SA NODAL PARASYMPATHECTOMY

Autonomic control of atrial rate was evaluated in anesthetized dogs by electrical stimulation of stellate ganglia and/or cervical vagi befor e and after the intrinsic cardiac right atrial ganglionated plexus (RA GP) was injected with the nicotinic blocker hexamethonium or the membr ane stabilizing chemical lidocaine, or the RAGP was surgically removed . Injections of lidocaine or hexamethonium into or surgical removal of the RAGP eliminated the bradycardia elicited by vagal stimulation wit hout reducing the tachycardia induced by stellate stimulation. Yet, af ter surgical ablation of the RAGP, the tachycardia induced by sympathe tic stimulation was still reduced by 94% by parasympathetic stimulatio n. After injections of hexamethonium or lidocaine into the RAGP were a dministered, the sympathetically induced tachycardia was reduced by 39 and 85%, respectively, by parasympathetic stimulation. After RAGP abl ation, when atrial rate was increased by infusion of beta-adrenergic a gonists, parasympathetic stimulation reduced atrial rate by 13%. Sinoa trial (SA) nodal parasympathectomy, produced by disrupting the RAGP, e liminates direct vagal control of the SA node while leaving prejunctio nal parasympathetic projections to sympathetic efferents innervating t he SA node intact.