Elevation of glutathione levels by ammonium ions in primary cultures of rat astrocytes

It is well established that ammonia is detoxified in the brain to form glut amine and that astrocytes play a major role in this process. The synthesis of glutamine requires glutamate and ATP. Since glutamate and ATP are also r equired for the synthesis of glutathione (GSH), we examined the effect of p athophysiological concentrations of ammonia on levels of GSH in primary cul tures of astrocytes. GSI-I content in the medium increased in a dose- and t ime-dependent manner in the presence of ammonia. After an initial decrease, cellular GSI-I content increased in a similar manner. The levels of glutat hione disulfide (GSSG) were also increased. A linear relationship was obser ved between ammonia concentration and the increase in GSH levels. An increa se in the efflux of GSH from cells into medium was also observed under thes e conditions. Buthionine sulfoximine and acivicin, but not methionine sulfo ximine, blocked the ammonia induced increase in GSH levels. No, or minor, c hanges in the activities of enzymes (gamma-glutamyl transpeptidase, GSH red uctase and GSH-peroxidase) that might influence GSH levels were identified and thus could not account for the ammonia induced increase in GSH levels i n astrocytes. These findings indicate that pathophysiological concentration s of ammonium ions result in increased astroglial levels of GSH which may a ffect the metabolism and function of astrocytes, Published by Elsevier Scie nce Ltd.