RESPONSE OF GLUTAMINE-METABOLISM TO EXOGENOUS GLUTAMINE IN HUMANS

To determine whether exogenous glutamine affects whole body glutamine metabolism, preliminary experiments were performed to verify that L-[1 -C-13]-, L-[U-C-14]-, and L-[3,4-H-3]glutamine given simultaneously by vein provided similar estimates of glutamine appearance rates [R(a); 355 +/- 24, 373 +/- 19, and 393 +/- 24 (SE) mu mol . kg(-1)h(-1), resp ectively, P = NS] in six healthy men; glutamine oxidation accounted fo r 32 +/- 3 and 51 +/- 5% (P < 0.01) of glutamine R(a) when it was meas ured using L-[U-C-14]- and L-[1-C-13]glutamine, respectively. Five sub jects received two 5-h intravenous infusions of L-[3,4-H-3]glutamine a nd a simultaneous nasogastric infusion of L-[1-C-13]glutamine on 2 sep arate days in the postabsorptive state, along with saline on 1 day and natural L-glutamine (856 +/- 45 mu mol . kg(-1). h(-1)) on another da y in a randomized order. Splanchnic glutamine extraction (deter mined from [C-13]glutamine appearance into systemic blood) reached 74 +/- 4 and 53 +/- 5% during the enteral infusion of tracer alone and in combi nation with a large load of glutamine, respectively. Glutamine infusio n was associated with increased plasma glutamine concentration (from 6 30 +/- 50 to 1,297 +/- 75 mu M), R(a) (from 258 +/- 20 to 589 +/- 45 m u mol . kg(-1). h(-1)), and oxidation (from 179 +/- 20 to 477 +/- 47 m u mol . kg(-1). h(-1), all P < 0.01), no change in glutamine release f rom proteolysis, and a decline in glutamine de novo synthesis (from 15 6 +/- 15 to 93 +/- 13 mu mol . kg(-1). h(-1)). We conclude that the re sponse to exogenous glutamine includes 1) a stimulation of glutamine o xidation and splanchnic extraction and 2) suppression of glutamine de novo synthesis.