Glutamine is the most abundant free
amino acid of the human body. In catabolic stress situations such as after operations,
trauma and during
sepsis the enhanced transport of
glutamine to splanchnic organs and to blood cells results in an intracellular depletion of
glutamine in skeletal muscle.
Glutamine is an important metabolic substrate for cells cultivated under in vitro conditions and is a precursor for
purines,
pyrimidines and
phospholipids. Increasing evidence suggests that
glutamine is a crucial substrate for immunocompetent cells.
Glutamine depletion in the cultivation medium decreases the
mitogen-inducible proliferation of lymphocytes, possibly by arresting the cells in the G0-G1 phase of the cell cycle.
Glutamine depletion in lymphocytes prevents the formation of signals necessary for late activation. In monocytes
glutamine deprivation downregulates
surface antigens responsible for
antigen preservation and phagocytosis.
Glutamine is a precursor for the synthesis of glutathionine and stimulates the formation of
heat-shock proteins. Moreover, there are suggestions that
glutamine plays a crucial role in osmotic regulation of cell volume and causes phosphorylation of
proteins, both of which may stimulate intracellular
protein synthesis. Experimental studies revealed that
glutamine deficiency causes a necrotising
enterocolitis and increases the mortality of animals subjected to bacterial stress. First clinical studies have demonstrated a decrease in the incidence of
infections and a shortening of the
hospital stay in patients after
bone marrow transplantation by supplementation with
glutamine. In
critically ill patients parenteral
glutamine reduced
nitrogen loss and caused a reduction of the mortality rate. In surgical patients
glutamine evoked an improvement of several immunological parameters. Moreover,
glutamine exerted a trophic effect on the intestinal mucosa, decreased the intestinal permeability and thus may prevent the translocation of bacteria. In conclusion,
glutamine is an important metabolic substrate of rapidly proliferating cells, influences the cellular hydration state and has multiple effects on the immune system, on intestinal function and on
protein metabolism. In several disease states
glutamine may consequently, become an indispensable nutrient, which should be provided exogenously during artificial nutrition.