The reflex effects of hepatic low-pressure baroreceptors on renal and cardiopulmonary sympathetic efferent nerve activity were studied in mongrel dogs anesthetized with pentobarbital sodium. Systemic blood pressure, central venous pressure, hepatic, renal, and portal venous pressures were all measured during occlusion of the thoracic vena cava above the diaphragm, below the liver, and during occlusion of the portal vein. Renal and cardiopulmonary sympathetic efferent nerve activity was continuously recorded along with the hepatic efferent nerve activity during the caval occlusions. Hepatic baroreceptor excitation resulted in marked increases in hepatic afferent nerve activity and reflex increases in renal and cardiopulmonary sympathetic efferent nerve activity without a change in heart rate. Section of the anterior hepatic nerves eliminated the reflex increase in renal efferent nerve activity, but did not eliminate the increase in cardiopulmonary sympathetic efferent nerve activity. Carotid sinus denervation, bilateral cervical vagotomy, and phrenectomy did not alter the reflex responses to hepatic baroreceptor excitation. These hepatorenal and hepatocardiopulmonary reflexes may be important reflex mechanisms that are activated during congestive heart failure and cirrhosis of the liver.

Pericardial mechanoreceptors with afferents in the phrenic nerves were studied in anesthetized dogs. The specific aims determined 1) if pericardial receptors with phrenic afferents exist in the dog; 2) the stimuli needed to activate these receptors; 3) the anatomic distribution of these pericardial receptors; and 4) which pericardial layer contains the receptors. Afferent activity was recorded from the phrenic nerves while the pericardium was probed. In 15 of 18 animals, pericardial receptors were found on the right side. In 12 of 18 animals pericardial receptors were located on the left side. Most of the mechanoreceptors were found in a band that paralleled the pericardiophrenic attachment, in the fibrous layer of the pericardium, overlying the atria and atrioventricular grooves. Some receptors had a cardiac rhythm, whereas others were stimulated by the inflating lung. None of the receptors were chemosensitive to capsaicin, bradykinin, or saline. This study is the first to demonstrate that the pericardium of the dog contains mechanosensitive receptors which are innervated by the phrenic nerve.

Dogs were anesthetized with pentobarbital sodium and placed on positive-pressure ventilation. The right phrenic nerve and/or its C5 branch were prepared for afferent recording. The hepatic veins, hepatic parenchyma, diaphragm, and inferior vena cava were studied for mechanoreceptors using light pressure and stroking as the stimuli. Mechanosensitive areas were found in the hepatic veins, hepatic parenchyma of the right medial lobe, and inferior vena cava. The hepatic vein and inferior vena caval receptors are located in the same 1- to 2-cm region as the sphincters that are found in these vessels. This study presents the first experimental evidence for the existence of hepatic vein receptors, hepatic parenchymal receptors, and inferior vena caval mechanoreceptors with phrenic afferents in the dog. These sensory areas of the circulation may be involved in the neural control of venous return as well as mediating changes in intrahepatic and portal venous blood pressure during normal respiration.