title: Effect of erythrocyte binding on elimination of harmol by the isolated perfused rat liver.
abstract: The effect on the hepatic elimination rate of drug bound to erythrocytes and to albumin was compared with harmol, a relatively hydrophilic drug of high hepatic intrinsic clearance, in the single-pass isolated perfused rat liver preparation (n = 12). The steady-state hepatic extraction ratio (E) of harmol (50 microM) was measured during three consecutive 35-min periods with three different perfusates: Krebs-Henseleit buffer, buffer containing bovine serum albumin (2%), and buffer containing washed human erythrocytes (10%) perfused at 5 mL/min/g liver in randomized order. The mean unbound fraction (fu) of harmol in the latter two perfusates was 0.55 +/- 0.07 and 0.62 +/- 0.08, respectively, and the mean E for the three perfusates were 0.85 +/- 0.06, 0.62 +/- 0.07, and 0.71 +/- 0.08, respectively. The sinusoidal model fitted the relationship between E and fu better than the venous equilibrium model. Four further experiments, with perfusates of buffer, buffer + 2% albumin, and buffer + 4% albumin, confirmed that harmol elimination conformed to the sinusoidal model. For each of the 12 experiments that used erythrocyte perfusate, E and fu data from each of the two non-erythrocyte perfusates were used to predict E for the erythrocyte perfusate at the observed fu of 0.62, with the sinusoidal model. There was no significant difference between the observed (0.71 +/- 0.08) and predicted (0.68 +/- 0.10) E values (p > 0.05). This result suggests that release of harmol from erythrocytes is not a rate-limiting factor in the hepatic elimination of harmol, and that plasma membrane permeability does not contribute readily to a red cell carriage effect, at least with moderately polar and small molecules.
authors.affiliation: Department of Pharmaceutics, Monash University, Victoria, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Morgan
authors.forename: A
authors.initials: A
authors.lastname: Guttmann
authors.forename: R G
authors.initials: RG
authors.lastname: Watson
authors.forename: H
authors.initials: H
authors.lastname: Ghabrial
authors.forename: S L
authors.initials: SL
authors.lastname: Elliott
authors.forename: R A
authors.initials: RA
authors.lastname: Smallwood
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004912:Erythrocytes / Q000378:metabolism*; D006247:Harmine / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D010100:Oxygen / Q000008:administration & dosage / Q000378:metabolism; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D012710:Serum Albumin, Bovine / Q000378:metabolism
chemical_list: D012710:Serum Albumin, Bovine; C001326:harmol; D006247:Harmine; D010100:Oxygen