Dietary glutamine enhances murine T-lymphocyte responsiveness

To examine the effects of dietary glutamine on lymphocyte function, male mice aged 6 wk were fed for 2 wk one of three isonitrogenous, isocaloric diets, which varied in glutamine concentration. The control diet included 200 g casein/kg, providing 19.6 g glutamine/kg; the glutamine-enriched diet provided 54.8 g glutamine/kg partly at the expense of casein; and the alanine + glycine-enriched diet provided 13.3 g glutamine/kg. The plasma concentrations of a number of amino acids varied because of the diet fed. The plasma glycine concentration was greater in mice fed the alanine + glycine-enriched diet (380 +/- 22 micromol/L) than in mice fed the control (177 +/- 17 micromol/L) or the glutamine-enriched (115 +/- 18 micromol/L) diets. The plasma glutamine concentration was greater in mice fed the glutamine-enriched diet (945 +/- 117 micromol/L) than in those fed the diet enriched with alanine + glycine (561 +/- 127 micromol/L), but was not different from that in mice fed the control diet (791 +/- 35 micromol/L). There was a significant linear relationship between the amount of glutamine in the diet and plasma glutamine concentration (r = 0.655, P = 0.015). Plasma alanine concentration was unaffected by diet. The reason for the lack of effect of increasing the amount of alanine in the diet upon its concentration in the circulation may relate to its use by the liver. Thymidine incorporation (56 +/- 18 kBq/well versus