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By participating in glutathione (GSH) synthesis, gamma-glutamyl transpeptidase (GGT) influences the GSH redox cycle, which is a major contributor in protecting against reactive oxygen metabolites. This study determined the effect of prolonged exposure of neonatal rats to > 98% oxygen on expression of GGT and on GSH metabolism. Lungs of neonatal rats chronically exposed to hyperoxia had increased expression of GGT mRNA, resulting in significantly higher GGT protein levels and enzyme activity than in lungs of animals raised in room air. Hyperoxia also upregulated glucose-6-phosphate dehydrogenase, but Na-K-ATPase activity was not changed. GGT mRNA, protein level, and enzyme activity returned to control levels after recovery in room air for 3 days. Levels of GSH, glutathione disulfide, and protein-bound GSH (S-glutathiolated protein) rose with hyperoxia and fell during recovery. S-glutathiolation is likely a mechanism for protection and a regulatory modification of protein sulfhydryl groups. Hyperoxia-induced upregulation of GGT and the concomitant increase in protein S-glutathiolation appear to be additional components fundamental in protecting the lung against oxidative injury.

The aerobic production of lactate from glucose by the intestine has been proposed as an important source of carbon substrate for liver glycogen synthesis. In order to determine the significance of aerobic and anaerobic lactate production by jejunal villus cells, we determined lactate production and energy charge (EC), an indicator of intracellular oxygen availability and oxidative phosphorylation activity, in jejunal villus cells under aerobic and anaerobic conditions. Adult rat villus cells were incubated in a polarographic chamber containing Krebs Ringer Phosphate Buffer, 5 mM glutamine, 5 mM glucose and 5 mg/ml BSA. The rate of O2 consumption was determined using a Clark electrode. Aliquots of assay mixture were removed and analyzed for lactate, ATP, ADP and AMP conc, after 5 periods (5 min (aerobic), 4 min (anaerobic-O2 sat