Studies of Sulfobromophthalein Sodium (BSP) Metabolism in Man. III. Demonstration of a Transport Maximum (Tm) for Biliary Excretion of BSP*

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Abstract
Direct evidence was presented supporting the concept of a transport rate maximum (Tm) for biliary excretion of BSP in man. The Tm for BSP determined colorimetrically in bile was 86% of the Tm estimated by the method of Wheeler et al from serum BSP concentrations during continuous infusions of the dye. Of infused BSP, 92% was recovered or accounted for. Whether there are separate Tin''s for free BSP and BSP conjugates has not been determined. Infusion of BSP at the theoretical Tm resulted in a steady state of serum BSP concentration while colorimetrically determined maximal biliary excretion remained constant. The constant Tm was not altered by sudden increase of serum BSP, indicating accumulation of BSP in the liver, and was likewise unchanged by sudden decrease of serum BSP, indicating depletion of stored dye.