Parasympathetic control of right atrial pressure in anesthetized dogs

We investigated whether the intracardiac parasympathetic ganglia for sinoatrial (SA) nodal pacemaker cells control the right atrial contractility selectively and totally in the autonomically decentralized heart of the open-chest anesthetized dog. Stimulation of the intracardiac parasympathetic nerves to the SA nodal area (SAP Stim) decreased the right atrial pressure (a wave pressure) and its first pressure derivative (dP/dt) as well as the atrial rate but did not change the atrioventricular (AV) conduction time. Stimulation of right and left cervical vagosympathetic complexes (CV Stim) decreased the a wave pressure, dP/dt, and atrial rate and prolonged the AV conduction time. When SAP and CV Stim decreased the atrial rate similarly, the decreases in a wave pressure and dP/dt in response to SAP Stim were less than those to CV Stim in unpaced and paced hearts. When treatment with hexamethonium bromide or tetrodotoxin into the SAP Stim locus abolished the decreases in atrial rate evoked by SAP and CV Stim, each treatment abolished the decrease in a wave pressure response to SAP Stim but only slightly attenuated the pressure response to CV Stim. These results demonstrate that right atrial pressure is modified by efferent parasympathetic neurons, which are located in a region that differs from that of efferent parasympathetic neurons controlling heart rate.