HEPATIC STORAGE AND EXCRETION OF SULFOBROMOPHTHALEIN SODIUM IN THE DOG *

Abstract

The hepatic removal rate of sulfobromophthalein sodium (BSP) was estimated in 14 dogs by measurements of hepatic blood flow (rotameter) and splanchnic arteriovenous concentration difference. During a constant BSP infusion, hepatic BSP removal reached a constant rate at an arterial concentration of 2 to 3 mg/100 ml even when the latter continued to rise. Sudden increments in arterial concentration produced a marked transient increase in hepatic BSP removal rate and decrements produced a transient reduction. Hepatic removal rate was higher during continuously rising than during constant arterial BSP concentrations. Hepatic excretion of BSP apparently depends upon a rate-limited transport mechanism and the quantity of BSP stored in the liver parenchyma depends directly upon the concentration in the surrounding plasma. A method for calculating the excretory transport maximum (Tm) and the relative storage capacity (S) was presented, based on observations during 2 different constant rates of BSP infusion. The calculated values of storage capacity indicate that BSP in the hepatic storage compartment is maintained at a concentration more than 8 times that in the plasma. In the range of plasma concentrations studied there was no evidence of "saturation" of the storage compartment. Extrahepatic removal rate of BSP is low enough so that Tm and S may be reasonably estimated from observations of peripheral plasma BSP concentrations during different rates of constant infusion, without resort to hepatic venous sampling or hepatic blood flow measurements.