Basolateral gamma-glutamyl transferase ectoactivity in rat liver: effects of chronic alcohol consumption

Abstract

Chronic alcohol consumption is known to increase hepatic gamma-glutamyl transferase (GGT) activity. The biological significance of this change has, however, remained unknown. Using a recently described methodology which allows the determination of basolateral ectoenzyme GGT activity (Ble-GGT) in perfused rat liver (Speisky et al, 1985), we have investigated the effects of chronic alcohol consumption on Ble-GGT and on its participation in the utilization of circulating glutathione (GSH). Ble-GGT was markedly increased (40-75%) by chronic alcohol consumption. The ecto-activity strongly correlated with total GGT activity, measured in whole liver homogenates from ethanol-fed animals (r = 0.898, p less than 0.001). Ble-GGT was found to catalyze the utilization of significant amounts of circulating GSH (7.4-14.7 nmol/min/100 g B.W.). Chronic ethanol treatment led to marked increases (111%) in the hydrolysis of circulating GSH, which highly correlated (r = 0.958, p less than 0.001) with total liver GGT activity. An increased Ble-GGT activity following chronic alcohol consumption might constitute a mechanism to increase the hepatic availability of GSH precursors.