Suitability criteria for compartmental analysis of the plasma clearance curve of exogenous cholephils. 131I Rose Bengal fulfils these criteria.

Hepatic clearance of exogenous cholephils involves at least three transfers : uptake by the liver, reflux from hepatocytes into the plasma, and intracellular transport followed by active secretion in bile. Compartmental analysis may be applied to the plasma disappearance curve in order to calculate the fractional transfer rates. The 131I Rose Bengal (131I RB) fills the requirements of such an analysis, contrary to bromsulphalein and indocyanine green, which have been used until now. 131I RB does not undergo enterophepatic cycle and is not metabolized by the liver. It behaves, in the preparation used, like a homogeneous substance, remains stable in the serum as long as 25 hours after its injection and may be bound completely with human albumin in vitro prior to administration : under these conditions, the material which is cleared by the liver is homogeneous. The use of tracer instead of loading doses, avoid any toxic effects on transport systems and results in plasma and liver concentrations which are negligeable in comparison with the Km of membrane transport, and are compatible with first order kinetics.