Role of glutamine in human carbohydrate metabolism in kidney and other tissues

Glutamine is the most abundant amino acid in the human body and is involved in more metabolic processes than any other amino acid. Until recently, the understanding of many aspects of glutamine metabolism was based on animal and in vitro data. However, recent studies using isotopic and balance techn iques have greatly advanced the understanding of glutamine metabolism in hu mans and its role in glucose metabolism in the kidney and other tissues. Th ere is now evidence that in postabsorptive humans, glutamine is an importan t glucose precursor and makes a significant contribution to the addition of new carbon to the glucose carbon pool. The importance of alanine for gluco neogenesis, viewed in terms of the addition of new carbons, is less than pr eviously assumed. It appears that glutamine is predominantly a renal glucon eogenic substrate, whereas alanine gluconeogenesis is essentially confined to the liver. As shown recently, renal gluconeogenesis contributes 20 to 25 % to whole-body glucose production. Moreover, glutamine has been shown not only to stimulate net muscle glycogen storage but also to stimulate glucone ogenesis in normal humans. Finally, in humans with type II diabetes, conver sion of glutamine to glucose is increased (more so than that of alanine). T he available evidence on the hormonal regulation of glutamine gluconeogenes is in kidney and liver and its alterations under pathological conditions ar e discussed.