THE USE OF A CONSTANT INFUSION OF [H-3] PHENYLALANINE TO MEASURE THE EFFECTS OF GLUTAMINE INFUSIONS ON MUSCLE PROTEIN-SYNTHESIS IN RATS GIVEN TURPENTINE

Skeletal muscle protein fractional synthetic rate (MPFSR) was measured in rats with a constant infusion of [H-3]phenylalanine to study the relationship between the rate of muscle protein synthesis in skeletal muscle and the intracellular glutamine concentration. The values for MPFSR (percentage per day) achieved in this study were in good agreement with those we have already reported with a flooding dose of [H-3]phenylalanine to measure MPFSR. This was the case both for control rats and for those that had been injected with turpentine (constant infusion 12.82 +/- 0.43% in saline-injected rats, 6.58 +/- 0.34% in rats injected with turpentine; flooding dose 12.88 +/- 0.73% in saline-injected rats, 7.04 +/- 0.67% in rats injected with turpentine). Therefore, there was no evidence for a stimulating effect of a flooding dose of phenylalanine on MPFSR, an effect that could have invalidated the conclusions drawn in our previous investigation. In this study, turpentine reduced the MPFSR by a mean of 49% (p < 0.001). This reduction in MPFSR was associated with a 39% reduction in the mean intramuscular glutamine concentration (p < 0.001). The reduction in intramuscular glutamine concentration was completely reversed by 5-h intravenous infusions of 0.22 M glutamine solutions, but there was no accompanying increase in the MPFSR. The results of this study therefore provide no evidence to support the proposal that an acute change in intramuscular glutamine concentration is a major factor in controlling the rate of protein synthesis in skeletal muscle.