PARASYMPATHETIC CONTROL OF RIGHT ATRIAL PRESSURE IN ANESTHETIZED DOGS

We investigated whether the intracardiac parasympathetic ganglia for s inoatrial (SA) nodal pacemaker cells control the right atrial contract ility selectively and totally in the autonomically decentralized heart of the open-chest anesthetized dog. Stimulation of the intracardiac p arasympathetic nerves to the SA nodal area (SAP Stim) decreased the ri ght atrial pressure (a wave pressure) and its first pressure derivativ e (dP/dt) as well as the atrial rate but did not change the atrioventr icular (AV) conduction time. Stimulation of right and left cervical va gosympathetic complexes (CV Stim) decreased the a wave pressure, dP/dt , and atrial rate and prolonged the AV conduction time. When SAP and C V Stim decreased the atrial rate similarly, the decreases in a wave pr essure and dP/dt in response to SAP Stim were less than those to CV St im in unpaced and paced hearts. When treatment with hexamethonium brom ide or tetrodotoxin into the SAP Stim locus abolished the decreases in atrial rate evoked by SAP and CV Stim, each treatment abolished the d ecrease in a wave pressure response to SAP Stim but only slightly atte nuated the pressure response to CV Stim. These results demonstrate tha t right atrial pressure is modified by efferent parasympathetic neuron s, which are located in a region that differs from that of efferent pa rasympathetic neurons controlling heart rate.