Changes in hepatic blood volume on galactose and indocyanine green uptake by cat liver

The liver has important functions as a blood volume reserve and in uptake and metabolism of many substrates. This study examines whether changes in hepatic blood volume modify the uptakes of model substrates galactose and indocyanine green (ICG) in cats anesthetized with pentobarbital sodium. A hepatic venous long-circuit technique with an extracorporeal reservoir was used to control hepatic flow and venous pressure and to allow repeated sampling of arterial, portal, and hepatic venous blood without depletion of the cat's blood volume. Hepatic blood volume was measured by plethysmography. Galactose and ICG were infused intravenously at constant rates for 200 min in each of three series of experiments. The first series were time controls. In the second series, hepatic blood volume was increased by raising hepatic venous pressure. In the third series hepatic blood volume was decreased by hepatic nerve stimulation and infusions of norepinephrine and angiotensin. Hepatic congestion resulted in small increases in blood galactose levels, suggesting mild impairment of hepatic galactose metabolism. Decreases in liver blood volume did not modify hepatic galactose metabolism. Increases in hepatic blood volume facilitated while decreases inhibited ICG uptake, but the effects were small. Sinusoidal velocity and transit time have minor effects on uptake even for protein-bound substrates. In summary, large changes in hepatic blood volume had minor effects on galactose and ICG blood concentrations, suggesting that the metabolic functions of the liver are essentially independent of the blood reservoir function.