Effect of glutamine infusions on glutamine concentration and protein synthetic rate in rat muscle

Studies were undertaken in sedated and unsedated rats to raise the depleted intramuscular glutamine concentrations produced by aseptic abscesses, and to assess the effect of this change on muscle protein fractional synthetic rate. Age- and weight-matched control animals were also included in the study. The rats were infused for up to 5 hours via the lateral tail vein with 1 mL/100 g of body weight per hour of either saline or 0.22 M glutamine. The intramuscular concentration of glutamine (mmol/L of intracellular water), which was reduced by 45% after turpentine in the sedated animals, was restored to within 79% of control values, but the muscle fractional protein synthetic rate, which was also reduced by 41% in these animals, was not improved by the glutamine infusions. Glutamine administration also failed to increase muscle protein synthesis in unsedated rats and in those supplemented with a liquid meal. It is concluded that acute elevations in muscle glutamine concentrations do not increase protein synthesis in this tissue and that therefore glutamine is unlikely to be a mediator in the control of muscle protein synthesis under these circumstances.