STIMULATORY EFFECT OF GLUTAMINE ON GLYCOGEN ACCUMULATION IN HUMAN SKELETAL-MUSCLE

To determine whether glutamine can stimulate human muscle glycogen syn thesis, we studied in groups of six subjects the effect after exercise of infusion of glutamine, alanine + glycine, or saline. The subjects cycled for 90 min at 70-140% maximal oxygen consumption to deplete mus cle glycogen; then primed constant infusions of glutamine (30 mg/kg; 5 0 mg . kg(-1). h(-1)) or an isonitrogenous, isoenergetic mixture of al anine + glycine or NaCl (0.9%) were administered. Muscle glutamine rem ained constant during saline infusion, decreased 18% during alanine glycine infusion (P < 0.001), but rose 16% during glutamine infusion ( P < 0.001). By 2 h after exercise, muscle glycogen concentration had i ncreased more in the glutamine-infused group than in the saline or ala nine + glycine controls (+2.8 +/- 0.6, +0.8 +/- 0.4, and +0.9 +/- 0.4 mu mol/g wet wt, respectively, P < 0.05, glutamine vs. saline or alani ne + glycine). Labeling of glycogen by tracer [U-C-13]glucose was simi lar in glutamine and saline groups, suggesting no effect of glutamine on the fractional rate of blood glucose incorporation into glycogen. T he results suggest that, after exercise, increased availability of glu tamine promotes muscle glycogen accumulation by mechanisms possibly in cluding diversion of glutamine carbon to glycogen.