COMPARISON OF THE HEPATIC-UPTAKE CLEARANCES OF 15 DRUGS WITH A WIDE-RANGE OF MEMBRANE PERMEABILITIES IN ISOLATED RAT HEPATOCYTES AND PERFUSED RAT LIVERS

The hepatic uptake clearances of 15 ligands with a wide range of permeabilities were determined in rats using two techniques: centrifugal filtration with isolated hepatocytes and the multiple indicator dilution (MID) method with isolated perfused livers. Some of the uptake clearance values were taken from the literature. Uptake clearance values obtained from isolated hepatocytes were extrapolated to that per gram liver (PS(inf,cell)), assuming that 1 g of liver has 1.3 x 10(8) cells. The values of PS(inf,cell) varied from approximately 0.1 to 72 (mL/min/g liver). The values of PS(inf,cell) were similar to those (PS(inf,MID)) determined by the MID method for ligands with uptake clearances below approximately q mL/min/g liver. However, for the ligands with larger uptake clearances, the PS(inf,MID) values were lower than the PS(inf,cell) values and appeared to reach an upper limit (approx. 15-20 mL/min/g liver). The PS(inf,cell) values of 1-propranolol, tetraphenylphosphonium (TPP+), and diazepam were 72, 43, and 22 mL/min/g liver, respectively, whereas their uptake clearances (PS(inf,MID)) determined by the MID method were 4 to 10 times lower. One of the possible mechanisms for this discrepancy is that an unstirred water layer, which may exist in Disse's space in isolated perfused livers (and probably under in vivo condition), limits the hepatic uptake rate of ligands with extremely high membrane permeabilities.