This study is undertaken to demonstrate that the shunt microdialysis probe is a valuable tool for profiling analytes in the rat bile duct while preserving enterohepatic circulation (EHC). Phenolphthalein (PT) is well known to be efficiently converted to its glucuronide adduct and enterohepatically cycled. Phenolphthalein glucuronide (PTG) has been used as marker to study both liver function and EHC. Using a microdialysis shunt probe, the concentration of PTG in the bile can be monitored. In this study, the PTG profiles were obtained in anesthetized rats with the bile flow either diverted or intact.Characterization of the PTG extraction efficiency (EE) using microdialysis showed that the in vitro EE of PTG was affected by the presence of bile salts, whereas the bile salts have no effect on the EE of caffeine. In addition, it was shown that the bile salt concentration must be balanced on both sides of the membrane in order to obtain the expected flow rate through the perfusion channel of the probe. A 2% solution of bile salts in Ringer's (BSR) was sufficient as the perfusate against rat bile in the shunt. With BSR as the perfusate, consistent in vitro EE results (by both recovery and delivery experiments) for PTG were obtained. These in vitro results compared favorably with EE values determined in vivo. Copyright (C) 1999 Elsevier Science B.V.
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