Transfer of oestrone glucuronide to the medium in an isolated rat liver perfusion system
Watanabe, H.; Menzies, J.A.
Journal of Pharmacy and Pharmacology 29(11): 695-696
1977
ISSN/ISBN: 0022-3573 PMID: 22605 Document Number: 116903
Estrogens are excreted predominantly via the biliary route in the rat and undergo an extensive enterohepatic circulation. While investigating the mechanism of estrone glucuronide transfer to bile in an isolated liver perfusion system, it became apparent that there was considerable transfer of the steroid in the direction of the perfusing medium. Recent studies have suggested that various organic compounds may be absorbed into the systemic circulation from the rat biliary tree. A study was undertaken to determine whether a similar absorptive process for the estrogen could account for its observed transfer to the medium. Even where the distended capacity was not exceeded, there was a measurable absorption of both erythritol and estrone glucuronide from the biliary tree. Recoveries in bile showed that the extent of absorption was similar for both compounds. In the case of the estrogen, however, hepatocellular binding appeared to hinder its transfer to the circulation. That portion which was retained in the liver was presumably more susceptible to transfer back to the bile, thus limiting net absorption from the biliary tree.