Changes in Splanchnic Hemodynamics Contribute to the Cardiovascular Responses Following Activation of Bradykinin‐Sensitive Pericardial Afferents

Sympathetic drive is a major controller of cardiovascular function. The heart performs an important sensory function via a variety of cardiac receptors that modulate cardiovascular responses by both neural and humoral reflexes. Bradykinin‐sensitive sympathetic afferent nerves from the heart can trigger marked increases in efferent sympathetic nerve activity to some cardiovascular target organs such as the kidney, arteries and veins. We reported previously that pericardial injection of bradykinin increased venous tone and cardiac output. The splanchnic vascular compartment plays an important role in control of venous return and cardiac output. This work tested the hypothesis that activation of bradykinin‐sensitive pericardial afferents modulates splanchnic hemodynamics. Sprague Dawley rats were anesthetized with a cocktail of alpha chloralose (80 mg/kg) and urethane (800 mg/kg). Catheters were placed in the femoral artery and vein to record arterial pressure (MAP) and heart rate (HR). A PE10 catheter was placed in the pericardial space for the injection of bradykinin (BK), an agent known to stimulate cardiac sympathetic afferents. The chest was closed and the rats allowed to breathe spontaneously. The portal vein and mesenteric artery were exposed via a midline laparotomy and fitted with transit time flow probes. After stabilization, the blood pressure, heart rate, portal venous flow (PF) and mesenteric flow (MF) responses to pericardial injection of BK or vehicle were recorded. Pericardial injection of saline vehicle had little effect (MAP: 2±2 mm Hg; HR: 13±6 bpm; PF: −5±1%; MF: −3±1%). In contrast, pericardial injection of BK (10 ug/kg) increased MAP (16±3 mm Hg) and HR (28±5 bpm). After an initial transient decrease, PF (10±2%) and MF (5±2%) were increased during the plateau phase of the MAP response (60–120 seconds). We interpret these data to indicate that activation of bradykinin‐sensitive pericardial afferents increases portal venous flow. This finding is consistent with the view that activation of the cardiac sympathetic afferent reflex elicits a venoconstrictor response to increase venous return from the splanchnic compartment. Support or Funding Information Supported by NIH R01 HL136741‐03, and the Basic Biomedical Sciences program of the Sanford School of Medicine.