Adequate levels of two neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate, are dependent on an adequate supply of glutamine to the central nervous system (brain and spinal cord). Glutamate does not cross the blood-brain barrier, but glutamine does. Glutamine treatment increases plasma and brain levels of glutamine, and serves as raw material for the production of glutamate and GABA for the central nervous system.
This study was done to determine whether circulating glutamine can alter GABA levels in brain tissues and in extracellular fluids. Neurotransmitter levels are, frequently, limited by the supply of the amino acids to produce them. (Tyrosine controls levels of catecholamines and tryptophan controls levels of serotonin in the central nervous system.)
This study demonstrated that glutamine circulating in the blood may partly regulate GABA levels in the brain and in extracellular fluid of the brain. This suggests that glutamine may be useful in the treatment of nervous system disorders, such as seizures, schizophrenia and anxiety, in which increased GABA activity is beneficial. .Glutamine treatment increased the extracellular GABA by 30% in the present study.
Confusion and reduced mental activity result from increased blood levels of ammonia during liver failure. It is possible that the hepatic encephalopathy and ammonia toxicity (generalized brain dysfunction seen in liver failure) could be due to elevated levels of glutamine causing an elevation in the levels of GABA in the brain. GABA receptor antagonists may be of benefit.
CONCLUSION: Glutamine was found, in rat studies, to increase GABA activity in the brain tissue and in the extracellular fluid of the brain. This supports the use of glutamine in conditions that benefit from increased GABA activity (seizures, schizophrenia and anxiety). This has not been studied clinically in humans.
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