GLYCINE CONJUGATION ACTIVITY OF BENZOIC-ACID AND ITS ACINAR LOCALIZATION IN THE PERFUSED-RAT-LIVER

Glycine conjugation activity toward benzoic acid (BA) was studied in t he single-pass perfused rat liver preparation. The steady-state hepati c extraction ratio for the portal vein (PV) perfused liver (at 10 ml/m in) was maximal (0.6) at input concentrations <40 mu M among perfusion s varying from tracer to 700 mu M. Glycine conjugation was the predomi nant pathway; the kinetic parameters estimated after appropriately cor recting for plasma protein binding (K-A = 8.37 X 10(3) M(-1) and 1.9 s ites) revealed a low K-m (12 mu M) and a moderately high V-max (101 nm ol.min(-1) g(-1) liver) system. Biliary excretion of BA and its glycin e-conjugated metabolite, hippuric acid, was minimal. Under first-order conditions (input concentration <2 mu M), the method of HAPV and HAHV perfusion (trace [C-14]benzoate delivered via the hepatic artery (HA) at 2 ml/min and blank perfusate via the portal vein (PV) or hepatic v ein (HV) at 10 ml/min) was used to examine the localization of glycine conjugation activity toward BA. During steady state, a multiple indic ator dose of Cr-51-labeled red blood cells (vascular marker), [Co-58]E DTA (interstitial space marker, which behaves similar to labeled trace r sucrose) and (H2O)-H-3 (cellular marker) was injected as a bolus int o the HA, Values of the extraction ratio of BA for HAPV perfusion (0.5 9 +/- 0.09) were dramatically reduced during HAHV perfusion (0.061 +/- 0.033, P < .01). Because labeled BA and the reference indicators ente ring via HA will reach virtually all sinusoidal spaces during HAPV but will be confined to the periportal region during HAHV, the sequestrat ion rate constants (intrinsic clearance per unit accessible cell water space) were normalized to the cellular water space accessed during HA PV and HAHV perfusions. Values of these rate constants for glycine con jugation during HAPV and HAHV perfusions, representing the activities for the whole liver and perioportal region, respectively, were 0.023 a nd 0.0043 ml.sec(-1) ml(-1). The HAHV:HAPV ratio of the sequestration rate constants (0.184) was markedly less than unity, suggesting that t he glycine conjugation activity for BA is primarily localized in the p erihepatic venous region of the rat liver.