Increased hepatic efflux of glutathione after chronic ethanol feeding

Chronic ethanol feeding increases hepatotoxicity of drugs, such as acetaminophen, which form electrophilic metabolites. Availability of glutathione (GSH) is important in preventing liver damage from reactive metabolites. Chronic ethanol feeding has been reported to increase turnover of hepatic GSH in rats. The results of the present study show that the total hepatic efflux of GSH was increased from 5.95 +/- 0.42 nmoles/min/g liver (control) to 9.96 +/- 0.57 nmoles/min/g (P less than 0.001) in isolated perfused livers from rats 24 hr after withdrawal from chronic ethanol feeding. The increase in total efflux of GSH was due to a significant increase in sinusoidal GSH efflux from 4.76 +/- 0.49 nmoles/min/g liver in control rats to 9.07 +/- 0.47 nmoles/min/g (P less than 0.001) in ethanol-fed rats, while biliary efflux decreased slightly, 1.20 +/- 0.11 (control) vs 0.89 +/- 0.31 (ethanol). The increase in cellular efflux of GSH was similar in magnitude to the increase in hepatic GSH turnover that we reported previously. Biliary GSSG was similar in both groups of animals. Hepatic GGT activity was increased slightly, but not significantly, whereas renal GGT activity was similar in ethanol-fed rats. Hepatic GSH and GSSG levels were also similar. The increase in turnover of hepatic GSH in rats withdrawn from chronic ethanol feeding was most likely due to increased cellular efflux of GSH. This finding suggests that chronic ethanol feeding may increase cellular requirements for GSH, although the mechanism remains unknown. This alteration in GSH turnover may have important consequences for detoxification of xenobiotics or their metabolites by the liver.