Brain glutamine synthetase activity and hyperoxia in neonatal rats

We have previously shown that exposure to 100% oxygen for 2 h results in a two-fold decrease in the brain glutamine synthetase activity of neonatal rats. The present study examines whether this decrement in enzyme activity leads to a global accumulation of glutamate, an excitotoxin which is a substrate for this enzyme. Despite a demonstrable decrement in whole brain glutamine synthetase activity, whole brain glutamate content is unaltered in animals exposed to 100% oxygen for 2 h. Furthermore, despite a persistent two-fold decrement in glutamine synthetase activity in animals exposed to 100% oxygen for 6 h, there remained no significant difference in glutamate content or in the glutamate/glutamine ratio between these animals and animals similarly exposed to room air. These results imply that the observed decrease in glutamine synthetase activity does not globally influence the glutamate content of the brain.