GLUTAMINE-ENRICHED TOTAL PARENTERAL-NUTRITION ENHANCES PLASMA GLUTATHIONE IN THE RESTING STATE

Glutathione (GSH) is the major intracellular antioxidant and is essent ial to normal cell function and replication. Cysteine and other thiol compounds have been considered rate-limiting for GSH biosynthesis, but recent studies have demonstrated that glutamine (GLN) becomes essenti al during metabolic stress to replete tissue GSH levels which have bec ome depleted. To determine the role of GLN supplementation in the rest ing, nonstressed state, we studied three groups of Wistar rats. The an imals were catheterized and randomly assigned to one of three groups: (1) chow ad libitum group receiving iv saline (control), (2) standard total parenteral nutrition (STA-TPN) group, and (3) glutamine-enriched TPN (GLN-TPN) group. The intravenously fed animals received no rat ch ow. The infusions were administered at a rate of 2.2 ml/hr for 4 days and all animals were harvested on the fifth day of study. The GLN-TPN group had a significantly higher plasma GSH level than STA-TPN or cont rol animals (P < 0.01). The hepatic concentration of GSH and the oxidi zed GSH/reduced GSH were similar in all groups. GLN-TPN had a signific antly lower plasma ALT level than the control group (P < 0.05). The co ntrol group had a significantly higher ALP level than STA-TPN and GLN- TPN animals (P < 0.01). There were no significant differences in other measures of hepatic functions among the three groups. Our data demons trate that in this model GLN-enriched TPN enhances plasma GSH concentr ations, while maintaining hepatic GSH stores. This suggests that GSH t urnover is altered during glutamine-enriched TPN, which may explain ho w dietary GLN supplementation enhances tissue antioxidant capacity. (C ) 1996 Academic Press, Inc.