Transport of drugs in isolated hepatocytes the influence of bile salts

Abstract

The influence of bile salts on hepatic transport of drugs was studied using isolated hepatocyte suspensions. Uptake of the organic anions, dibromosulphthalein (DBSP), indocyanine green (ICG) and an organic cation, N 4-acetyl procainamide ethobromide (APAEB) was measured. After 60 min incubation the amount of DBSP, ICG and APAEB present in the cells was 17, 41 and 4.5 per cent of the added amount respectively. The release of DBSP, ICG and APAEB from the hepatocytes preincubated with the agents under study, after 60 min incubation in fresh medium was 80.5, 12.5 and 48.9 per cent of the amount initially present respectively. The presence of bile canalicular membranes in the isolated hepatocytes was demonstrated by enzymehistochemistry: 5'-nucleotidase activity showed sharp branched bands over the cell surface. When bile salts were present in the incubation medium, the cellular content of DBSP, ICG and APAEB was diminished. The taurocholate concentration which caused 50 per cent of the maximal effect was 0.07 mM, 0.10 mM and 0.06 mM in experiments with DBSP, ICG and APAEB respectively. Pharmacokinetic analysis revealed that the influence of bile salts on cellular content of the three compounds was due to inhibition of the uptake into the isolated hepatocytes, rather than stimulation of release from the cells. The hypothesis, that stimulation of biliary output of organic anions in vivo is due to a modifying effect of bile salts on the canalicular membranes, instead of being the result of the increased bile flow, is not supported by this study.