Phagocyte functions in stressed rats: comparison of modulation by glutamine, arginine and ornithine 2-oxoglutarate

The effects of diets supplemented with 6.8 mmol⋅day^-1⋅kg^-1 glutamine, arginine or ornithine 2-oxoglutarate [ornithine α-ketoglutarate (OKG), a precursor of both glutamine and arginine] on phagocyte functions [i.e. H₂O₂ production by leucocytes and secretion of tumour necrosis factor α (TNFα) by stimulated macrophages] of stressed rats were studied. The relationship between the immunological effects of these amino acids and their plasma and tissue (muscle and intestine) concentrations was also explored. The catabolic model used consisted of injections of dexamethasone (DEX; 1.5 mg⋅day^-1⋅kg^-1) for 5 days. As previously described, DEX suppressed TNFα secretion in stimulated macrophages. Supplementation with arginine or OKG, but not glutamine, was able to counteract the DEX effect on TNFα secretion. Glutamine, arginine and OKG supplementation increased H₂O₂ production by monocytes and polymorphonuclear neutrophils from DEX-treated rats. All DEX-treated rats showed plasma and muscle glutamine depletion and also a decrease in the concentration of arginine in the gastrocnemius. Supplementation with glutamine, arginine or OKG was not able to counteract these depletions. It was concluded that glutamine, arginine and OKG improve phagocyte responses during stress, and that glutamine depletion is not necessarily associated with dysimmunity, since no correlation between glutamine tissue pools and the immune state was observed.