Glutamine is not found in food. It is primarily a brain fuel which can take the place of glucose. It is particularly abundant in the substantia nigra and thalamus of the brain, as well as in the blood, where its concentration is three to four times greater than all other amino acids. It is 10 to 15 times more concentrated in the cerebrospinal fluid than in the blood. In fasting or starvation states, when glycogen stores have been exhausted, large amounts of glutamine (and alanine) are released from muscle tissue and serve to shuttle amino acid nitrogen and carbon to other tissues. The carbon may be converted to glucose by the liver and made available for energy production.
In the 1960s an experiment was carried out supplementing 15 grams a day of L-glutamine to alcoholics. Compared with placebo, this was found to produce a significant improvement in control over alcohol consumption, but follow-up studies are lacking.
Glutamine also performs a major role in DNA synthesis. An influx of large amounts of glutamine may stimulate muscle protein synthesis. 60 per cent of the ammonia produced in the kidney tubules to buffer excessive urinary acidity comes from the breakdown of glutamine.