Do nonesterified fatty acids regulate skeletal muscle protein turnover in humans?
We examined whether elevated plasma nonesterified fatty acid (NEFA) levels exert a direct effect on protein metabolism by measuring [2H5]phenylalanine skeletal muscle exchange and whole body turnover. [2H5]phenylalanine was infused (0.5 mg.kg-1 x h-1) for 300 min in seven healthy subjects on two occasions. Intralipid (10%; 30 ml/h) or 0.154 mol/l NaCl was infused in random order from 120 min. Measurements were taken during basal (90-120 min) and infusion (270-300 min) periods. Intralipid infusion increased plasma NEFA levels [1.31 +/- 0.13 vs. 0.49 +/- 0.05 (SE) mmol/l; P < 0.05] and forearm NEFA uptake [45 +/- 76 vs. -51 +/- 44 nmol . 100 ml forearm-1 x min-1; P < 0.05]. Serum insulin and blood ketone body levels were similar with the two treatments. Elevated plasma NEFA levels were associated with a comparable decrease in forearm phenylalanine uptake (11 +/- 2 vs. 17 +/- 2 nmol x 100 ml forearm-1 x min-1; lipid vs. control, P < 0.05) and release (20 +/- 2 vs. 26 +/- 3 nmol x 100 ml forearm-1 x min-1; lipid vs. control, P < 0.05). However, there were no significant changes in net forearm phenylalanine exchange and whole body phenylalanine turnover. Therefore, elevated plasma NEFA levels were associated with a comparable decrease in the rates of skeletal muscle protein synthesis and breakdown but did not appear to influence overall protein balance, as assessed using [2H5]phenylalanine.
Walker
M
M
Department of Medicine, University of Newcastle upon Tyne, United Kingdom.
Shmueli
E
E
Daley
S E
SE
Cooper
B G
BG
Alberti
K G
KG
D000328:Adult; D005230:Fatty Acids, Nonesterified / Q000097:blood / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000098:blood supply; D006801:Humans; D008297:Male; D008954:Models, Biological; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism; D012039:Regional Blood Flow
D005230:Fatty Acids, Nonesterified; D009124:Muscle Proteins; D010649:Phenylalanine