Not picking sides and not trying to argue, but it is my understanding that intravenous glutamine was given to patients going through surgery to prevent muscle loss do to the amount of stress placed on the immune system by the surgery itself. Now, oral glutamine would not work the same way as intravenous glutamine, but if taken in powder form, in high doses, 10g - 20g, some of it may make it to the bloodstream before it is destroyed in your digestive track. I personally add 10g to 20g of glutamine to my post-workout Whey Isolate shake, more as an anti-catabolic supplement.
As for scientific sources, here are some articles by AST. Yes, they do sell glutamine, but they do list their sources unlike most supplement companies out there.
So many benefits from Glutamine
www.ast-ss.com/research/cribb/research_reviews/rr_full_text.asp?rrID=446Source: Journal of Cell Physiology, 2005.
Glutamine supplementation prevents destruction of immune cells
www.ast-ss.com/research/cribb/research_reviews/rr_full_text.asp?rrID=370Source: Med Sci Sports Exerc, 36:210-217, 2004
Consistent, daily glutamine supplementation is the key.
www.ast-ss.com/research/cribb/research_reviews/rr_full_text.asp?rrID=146The Journal of Strength and Conditioning Research. 16(1);157–160, 2002.
Supplementing with glutamine enhances muscle glycogen synthesis.
www.ast-ss.com/research/cribb/research_reviews/rr_full_text.asp?rrID=103J.Appl.Physiol.86;6:1770-1777, 1999.
Glutamine supplementation enhances whey's effect on protein synthesis rates in muscle.
www.ast-ss.com/research/cribb/research_reviews/rr_full_text.asp?rrID=14Nutrition 2001 Jan;17(1):35-40