Hepatocytes of Zones 1 and 3 Conjugate Sulfobromophthalein with Glutathione

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Abstract
The capacity of hepatocytes of Zones 1 and 3 of the liver acinus to conjugate sulfobromophthalein (BSP) with glutathione and to secrete the conjugate into bile was studied. BSP was infused into the insituperfused rat liver in concentrations of 0.01 and 0.05 mM. Perfusions were performed either in the portal to hepatic vein direction (forward perfusion) or in the hepatic vein to portal vein direction (retrograde perfusion). Hepatocytes contributing to the uptake, metabolism and biliary secretion of BSP were directly assessed qualitatively by light microscopy, and also semi-quantitatively by microspectrophotometry. BSP was taken up predominantly by hepatocytes of Zone 1 during forward perfusion and by those of Zone 3 during the retrograde perfusion of BSP. The biliary products of BSP metabolism by each acinar zone were subsequently assessed. Hepatocytes of both Zones 1 and 3 of the acinus secreted BSP into bile in the form of BSP-glutathione, and BSP-glutathione conjugate represented about 78% of the total BSP secreted into bile by each zone. The rate of BSP biliary secretion by both zones was similar at a concentration of 0.01 mM BSP, while a slight decrease (15%) in BSP secretory rate by hepatocytes of zone 3 was observed at concentrations of BSP near biliary Tm. Liver perfusion with exogenous BSP-glutathione provided results similar to those obtained with BSP. In contrast, the perfusion of 3,6-dibromosul-phthalein, a compound which is not conjugated by hepatocytes, resulted in similar biliary secretory rates regardless of the direction of perfusion. These results indicate that: (a) the capacity for glutathione conjugation of BSP is distributed among hepatocytes of all acinar zones; (b) near biliary Tm, the biliary secretory rate of BSP by hepatocytes of Zone 3 is slower than that of hepatocytes of zone 1, and (c) in vivo, all hepatocytes likely contribute to the uptake, metabolism and biliary secretion of BSP.