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

The effects of diets supplemented with 6.8 m mol . day(-1) . kg(-1) glutami ne, arginine or ornithine 2-oxoglutarate [ornithine alpha-ketoglutarate (OK G), a precursor of both glutamine and arginine] on phagocyte functions [i.e . H2O2 production by leucocytes and secretion of tumour necrosis factor alp ha (TNF alpha) by stimulated macrophages] of stressed rats were studied. Th e relationship between the immunological effects of these amino acids and t heir plasma and tissue (muscle and intestine) concentrations was also explo red. The catabolic model used consisted of injections of dexamethasone (DEX ; 1.5 mg . day(-1) . kg(-1)) for 5 days. As previously described, DEX suppr essed TNFa secretion in stimulated macrophages. Supplementation with argini ne or OKG, but not glutamine, was able to counteract the DEX effect on TNF alpha secretion. Glutamine, arginine and OKG supplementation increased H2O2 production by monocytes and polymorphonuclear neutrophils from DEX-treated rats. AII DEX-treated rats showed plasma and muscle glutamine depletion an d also a decrease in the concentration of arginine in the gastrocnemius. Su pplementation with glutamine, arginine or OKG was not able to counteract th ese depletions. It was concluded that glutamine, arginine and OKG improve p hagocyte responses during stress, and that glutamine depletion is not neces sarily associated with dysimmunity, since no correlation between glutamine tissue pools and the immune state was observed.