BLOOD MOBILIZATION FROM THE LIVER OF THE ANESTHETIZED DOG

The abdominal circulation contains a high proportion of the total bloo d volume and this can change either passively in response to changes i n vascular distending pressure or actively (termed a capacitance respo nse) to changes in sympathetic nervous activity. The liver is the larg est abdominal organ and this study was designed to evaluate its potent ial contribution to overall vascular capacitance and compliance. In ch loralose anaesthetized dogs, the liver was vascularly isolated, perfus ed through the portal vein and hepatic artery at either constant press ures or constant flows and drained from the hepatic veins at constant pressure. Changes in vascular resistance were assessed from changes in inflow pressures or flows and hepatic blood volume was determined by differences between net inflow and outflow. During constant flow perfu sion the change in hepatic volume (capacitance change) in response to supramaximal stimulation of sympathetic nerves at 16 Hz was (mean +/- S.E.M.) -2.40 +/- 0.61 ml (kg body weight)(-1). This response was not significantly different during constant pressure perfusion. The change s in portal venous and hepatic arterial pressures during stimulation a t constant flow perfusion were +0.67 +/- 0.13 and +4.92 +/- 0.67 kPa, respectively. The compliance of the liver, assessed as the change in v olume to a change in hepatic venous pressure, was +5.44 +/- 0.18 ml kg (-1) kPa(-1). These results indicate that the liver has a major capaci tance role, comparable to that of the canine spleen and, in addition, is highly compliant. No evidence was found to suggest that a sphincter on the hepatic outflow exists. Assuming similar responses occur in hu mans, who do not possess a large contractile spleen, the liver would b e the most important controllable blood reservoir in the body.