There is some evidence, although controversial, that the intracellular glutamine concentration controls the net balance of protein synthesis and protein degradation in the muscle cell. In vitro it can be shown that increasing muscle glutamine stimulates net protein synthesis, while decreasing it stimulates net proteolysis. This has been very difficult to demonstrate in vivo, but it is a consistent finding that hypercatabolic states are associated with low muscle glutamine and increased net proteolysis. Thus it is proposed that injury signals muscle to release glutamine, the drop in muscle glutamine results in increased net proteolysis which provides more sustrate for glutamine synthesis.
The rationale for using glutamine is that by giving it exogenously you will decrease the need to make it endogenously and if you dont need to make glutamine you dont need to breakdown as much protein ( which we presume to be a good thing). So if you could maintain those muscle glutamine levels very high then this should shut off proteolysis, and may even promote protein synthesis. The easiest method to do this would be to feed large amounts of glutamine by mouth but this is not usually possible in many of these conditions. However, where possible it has been used - up to 40 grams of glutamine per day, and appears to have beneficial effects (at these levels the glutamine overloads the capacity of the small intestine to catabolize it and it results in a rise in circulating glutamine levels.
**I got this info from my teachers lecture notes from my Advanced Nutrition class.
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