Simultaneous blood and biliary sampling of esculetin by microdialysis in the rat

Biliary excretion and intestinal reabsorption in enterohepatic circulation play major dispositional roles for some drugs. To circumvent multiple blood sampling and interruption of enterohepatic circulation in conventional biliary cannulation, the present study utilized the minimally invasive sampling technique of microdialysis in pharmacokinetics and biliary excretion studies. Microdialysis probes were inserted into the jugular vein and bile duct in the anesthetized rat for simultaneous and continuous sampling following intravenous administration of esculetin, a bioactive coumarin derivative. Placements of the microdialysis probes were designed to minimize obstruction to normal flows of the body fluids. Separation and quantitation of esculetin in the dialysates were achieved using high performance liquid chromatography (HPLC) coupled to UV detection. The results indicated higher drug concentrations in the bile than in the blood, suggesting active biliary excretion. The study also provided an example of successful application of in vivo microdialysis as an interesting and feasible alternative for pharmacokinetics and biliary drug excretion studies.