Evidence for reversible sequestration of morphine in rat liver

Transport of fluorescent bile acids by the isolated perfused rat liver: kinetics, sequestration, and mobilization

Hepatocyte transport of six fluorescent bile acids containing nitrobenzoxadiazolyl (NBD) or a fluorescein derivative on the side chain was compared with that of natural bile acids using the single-pass perfused rat liver. Compounds were infused at 40 nmol/g liver min for 15 minutes; hepatic uptake and biliary recovery were measured; fractional extraction, intrinsic basolateral clearance, and sequestration (nonrecovery after 45 minutes of additional perfusion) were calculated. Fluorescent bile acids were efficiently extracted during the first 3 minutes (70%-97%), but net extraction decreased with time mostly because of regurgitation into the perfusate. For cholylglycine and ursodeoxycholylglycine (UDC-glycine), extraction was 94% to 99%, and regurgitation did not occur. Intrinsic hepatic clearance of fluorescent bile acids (2-7 mL/g liver x min) was lower than that of cholylglycine (9.0 +/- 0.6; mean +/- SD) and UDC-glycine (21.4 +/- 0.4). Sequestration at 60 minutes was 8% to 26% for fluorescent bile acids with a cholyl moiety (cholylglycylaminofluorescein [CGamF], cholyllysylfluorescein [C-L-F], cholyl-[N epsilon-NBD]-lysine [C-L-NBD], and cholylaminofluorescein [CamF]), 32% for ursodeoxycholylaminofluorescein (UDCamF), and 88% for ursodeoxycholyl-(N epsilon-NBD)lysine (UDC-L-NBD). Cholylglycine and UDC-glycine had <3% retention. Biliary secretion of sequestered UDCamF, but not of UDC-L-NBD, was induced by adding dibutyryl cyclic adenosine monophosphate (DBcAMP) to the perfusate, possibly by translocation to the canaliculus of pericanalicular vesicles containing fluorescent bile acids. Biliary secretion of UDC-L-NBD, but not of UDCamF, was induced by adding cholyltaurine or UDC-taurine, possibly by inhibition of binding to intracellular constituents or of transport into organelles. It is concluded that fluorescent bile acids are efficiently transported across the basolateral membrane, but in contrast to natural conjugated bile acids, are sequestered in the hepatocyte (UDC derivatives > cholyl derivatives). Two modes of hepatic sequestration of fluorescent bile acids were identified. Fluorescent bile acids may be useful to characterize sequestration processes during bile acid transport through the hepatocyte.

A priming dose of propranolol reduces the availability of a subsequent dose in the isolated perfused rat liver preparation

1. A 50 microL bolus dose containing (+/-)-propranolol hydrochloride (200 microg) and [14C]-sucrose, or antipyrine (2 mg) and [14C]-sucrose, or [14C]-taurocholate sodium was injected into the portal vein of the isolated perfused rat liver preparation and perfusate outflow samples were collected frequently for the next 30 min. After a 20 min washout period this procedure was repeated. 2. [14C]-Sucrose, antipyrine and [14C]-taurocholate each eluted as a single peak at 18, 31 and 28 s, respectively, after each dose. In contrast, propranolol eluted with two peaks at approximately 18 and 128 s after dosing. 3. There was no significant difference in dose-corrected area under the outflow curve (AUC) for [14C]-sucrose, antipyrine or [14C]-taurocholate between the first and second doses whereas the mean propranolol AUC for the second dose was only 0.577+/-0.439 that for the first dose (P<0.05). 4. Unmetabolized propranolol accounted for more than 80% of the drug in hepatic tissue for the first and second doses at 18 s and greater than 50% at 128 s, and there was no significant difference in these values at each time between the first and second doses. 5. These findings suggest that for an avidly extracted drug, such as propranolol, systemic availability of orally administered drug will be highly dependent on factors that influence the hepatic tissue binding of the drug.