RETROGRADE PERFUSION TO PROBE THE HETEROGENEOUS DISTRIBUTION OF HEPATIC DRUG-METABOLIZING-ENZYMES IN RATS

Abstract

The elimination of [14C]acetaminophen which was formed from [14C]phenacetin was slower than that for the preformed metabolite, [3H]acetaminophen. This may be due to the uneven distribution of enzyme systems for O-deethylation in the formation of acetaminophen and sulfate-conjugation of aceteminophen in the liver parenchyma. Retrograde perfusion which reversed the direction of hepatic flow into the liver and the location the enzyme systems with respect to the flow path, was used to examine the elimination kinetics of [14C]acetaminophen and [3H]acetaminophen. In the same rat liver preparation, both [14C]phenacetin and [3H]acetaminophen in tracer concentrations were delivered simultaneously into the perfused rat liver in situ preparation with normal directional flow (into the portal vein and out of the hepatic vein). The direction of flow was then reversed to retrograde perfusion (into the hepatic vein and out of the portal vein) which was later reverted back to normal perfusion. The elimination of [14C]acetaminophen was again slower than the elimination of [3H]acetaminophen during normal perfusion, but the elimination kinetics were virtually identical for both metabolite species during retrograde perfusion. Sulfate-conjugation occurred predominantly in the periportal region while O-deethylation occurred preferentially in the centrilobular region of the liver and showed that retrograde perfusion was a useful probe in the investigation of the uneven distribution of hepatic drug-metabolizing enzyme systems.