Glutamine: The pivot of our nitrogen economy?

Glutamine serves as a shuttle of useful nontoxic nitrogen, supplying nitrog en from glutamine-producing (eg, muscle) to glutamine-consuming tissues. Tr ue production rates of glutamine are difficult to measure, but probably are less than 60 to 100 g/d for a 70-kg man. During catabolic stress increased amounts of glutamine are released from muscle, consisting of protein deriv ed glutamine, newly synthesized glutamine, and glutamine losses from the in tramuscular free pool. The large and rapid losses of free muscle glutamine are difficult to restore, presumably as a result of disturbances in the Na electrochemical gradient across the cell membrane. Whereas increased amoun ts of glutamine are released from muscle, glutamine consumption by the immu ne system (liver, spleen) also is enhanced. Thus, during catabolic stress c hanges occur in the flow of glutamine between organs: These changes are not necessarily reflected by alterations in the whole-body appearance rate of glutamine. In contrast with the gut, where glutamine is taken up in a conce ntration dependent manner, the immune system actively takes up glutamine de spite decreased plasma concentrations. Supplementation with glutamine influ ences uptake by both the gut and the immune system, as evidenced by increas ed mucosal glutamine concentrations and gut glutathione production. There i s evidence suggesting that this improves gut barrier function. Although the benefit of glutamine supplementation is most evident from experimental stu dies, clinical studies on the effect of glutamine do exist and suggest that glutamine supplementation has beneficial effects with regard to patient ou tcome.