Blockade of Cardiac Nerves by Intrapericardial Local Anaesthetics in the Conscious Rabbit

Local anaesthetic drugs were instilled into the pericardial sac of conscious rabbits through a chronically implanted catheter. Twenty mg of procaine HCl always caused complete blockade of cardiac vagal and sympathetic efferent nerves, tested by eliciting the baroreceptor-heart rate reflex, and abolished the reflex depression of renal sympathetic nerve activity elicited by impeding left ventricular outflow. It also slowed heart rate by a direct effect on the sinoatrial pacemaker. When the same dose of procaine was given intravenously there were only transient changes in blood pressure, heart rate and the baroreceptor-heart rate reflex. Lignocaine HCl and bupivacaine HCl were relatively less effective in blocking cardiac sympathetic efferent nerves. Intrapericardial procaine can be used in conscious animals to elucidate the part played by the cardiac receptor reflexes in control of the circulation.