Expression pattern of glutamine synthetase marks transition from collecting into conducting hepatic veins

The expression of glutamine synthetase (GS) is confined to a rim of hepatoc ytes surrounding the efferent hepatic Veins in all mammalian species invest igated. In rat liver, a two- to three-cell thick layer of GS-positive (GS()) hepatocytes uniformly surrounds the two to four terminal branching gener ations of the hepatic vein that collect blood from sinusoids (central veins ). With increasing diameter of the efferent vessel, this multilayered rim o f GS(+) hepatocytes becomes confined to patches surrounding the decreasing number of central vein outlets. The remaining part of the wall of these sub lobar hepatic Veins is bordered by a one-cell thick layer of GS(+) hepatocy tes. Around still larger veins, this single-cell layer of GS(+) hepatocytes gradually disappears. The expression pattern of GS is therefore a convenie nt biological parameter to delimit sinusoidal draining ("collecting") from nondraining ("conducting") surfaces in the wall of the efferent hepatic ves sels. The hepatocytes surrounding a single tree of central veins together f orm a compound-liver lobule.