Blood flow and norepinephrine effects on liver vascular and extravascular volumes

The relative effects of changes in hepatic blood flow and in levels of sympathetic activity on liver volumes were ascertained by use of multiple-indicator dilution studies. Portal vein-hepatic vein dilution patterns were obtained following injection of a mixture containing 51Cr-labeled red blood cells (a vascular reference) and 14C-labeled sucrose (a reference extracellular substance). Hepatic blood volume was calculated as the product of liver blood flow and red cell transit times, and interstitial space as the product of plasma flow and the difference between labeled sucrose and red cell transit times. Concentrations of norepinephrine and epinephrine were measured in aorta, portal vein, and hepatic vein. Hepatic blood volume and interstitial space increased with increased blood flow; and elevated plasma norepinephrine levels, especially in portal vein (following either exogenous infusion or activation of peripheral sympathetic fibers) selectively reduced the distending effect of hepatic inflow on the vascular volume. The data provide a description of the in vivo variation in canine liver vascular and interstitial volumes with blood flow and sympathetic activation.