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Provides information on a study which evaluated an approach for determining skeletal muscle-specific glucose flux using radioactive stereoisomers and the microdialysis technique. Methods; Results; Discussion.

We have tested the hypothesis that transit through the interstitial fluid, rather than across cell membranes, is rate limiting for amino acid uptake from blood into muscle in human subjects. To quantify muscle transmembrane transport of naturally occurring amino acids, we developed a novel 4-pool model that distinguishes between the interstitial and intracellular fluid compartments. Transport kinetics of phenylalanine, leucine, lysine, and alanine were quantified using tracers labeled with stable isotopes. The results indicate that interstitial fluid is a functional compartment insofar as amino acid kinetics are concerned. In the case of leucine and alanine, transit between blood and interstitial fluid was potentially rate limiting for muscle amino acid uptake and release in the postabsorptive state. For example, in the case of leucine, the rate of transport between blood and interstitial fluid compared with the corresponding rate between interstitial fluid and muscle was 247 ± 36 vs. 610 ± 95 nmol·min-1·100 ml leg-1, respectively (P < 0.05). Our results are consistent with the process of diffusion governing transit from blood to interstitial fluid without selectivity, and of specific amino acid transport systems with varying degrees of efficiency governing transit from interstitial fluid to muscle. These results imply that changes in factors that affect the transit of amino acids from blood through interstitial fluid, such as muscle blood flow or edema, could play a major role in controlling the rate of muscle amino acid uptake. [ABSTRACT FROM AUTHOR]

This investigation evaluated the physiological impact of different dietary protein intakes on skeletal muscle protein synthesis postexercise in endurance runners. Five endurance-trained, male runners participated in a randomized, crossover design diet intervention, where they consumed either a low (0.8 g/kg; LP)-, moderate (1.8 g/kg; MP)-, or high (3.6 g/kg; HP)-protein diet for 4 wk. Diets were designed to be eucaloric with carbohydrate, fat, and protein approximating 60, 30, and 10%; 55, 30, and 15%; and 40, 30, and 30% for LP, MP, and HP, respectively. Substrate oxidation was assessed via indirect calorimetry at 3 wk of the dietary interventions. Mixed-muscle protein fractional synthetic rate (FSR) was measured after an endurance run (75 rain at 70% VO2 peak) using a primed, continuous infusion of [²H5]phenylalanine. Protein oxidation increased with increasing protein intake, with each trial being significantly different from the other (P « 0.01). FSR after exercise was significantly greater for LP (0.083%/h) and MP (0.078%/h) than for HP (0.052%/h; P « 0.05). There was no difference in FSR between LP and MP. This is the first investigation to establish that habitual dietary protein intake in humans modulates skeletal muscle protein synthesis after an endurance exercise bout. Future studies directed at mechanisms by which level of protein intake influences skeletal muscle turnover are needed. [ABSTRACT FROM AUTHOR]

Presents a study that examined the time course changes in serum insulin concentrations in food-deprived rats after an oral bolus of leucine. Examination of the contribution of changes in serum concentrations of insulin to the increase in protein synthesis; Circulating insulin concentrations in food-deprived rats infused with somatostatin and leucine; Chemical essential for the enhanced rates of protein synthesis observed in skeletal muscle after food intake.

Examines the potential mechanism contributing to the inhibition of protein synthesis in skeletal muscle and heart after administration of tumor necrosis factors-α in rats. Reason behind reduction in synthesis of microfibrillar and sarcoplasmic proteins; Study of eukaryotic initiation factors and elongation factors; Relation between heart and skeletal muscle protein synthesis and messenger ribonucleic acid translational efficiency.