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Table 1 Effects of leucine supplementation on animal e human studies related to skeletal muscle protein turnover

From: Potential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studies

Study Duration Dose Methods Results
Human
4 180 min L-leucine: 1.09 and or 1.74 μmol/kg/min with insulin (plasma: 208 and 207 μmol/L) (infusion) Leucine + KIC rates of appearance; KIC oxidation; Leucine-carbon flux Leucine 1.09 μmol/kg/min stimulated leucine deposition into body protein in 37.7% but did not suppress endogenous proteolysis; Leucine 1.74 μmol/kg/min with insulin had a cumulative effect of 49.9% on net leucine deposition into body protein.
5 7 h L-leucine: 154 ± 1 mmol/kg-1/h-1 (infusion) Whole-body valine and phenylalanine (tracers) flux Inhibition of protein degradation without causing an increase in protein synthesis.
6 16 h BCAA: 1.66 μmol/kg/min (infusion) Whole-body (arterial and venous) leucine and phenylalanine (tracers) flux rates Suppressed rate of whole-body (-37%) and forearm (-43%) muscle proteolysis.
Rat
8 105 min BCAA: 246 mg/kg-1/h-1 (infusion) - Neither muscle protein synthesis nor breakdown affected.
9 NR L-leucine: 0.1, 0.2, 0.25 and/or 0.5 mM (muscle incubation) Rate of 14CO2 and KIC production Protein synthesis was stimulated in: 10% (0.1 mM), 19% (0.2 mM) and 42% (0.5 mM); Protein degradation was inhibited in: 0% (0.1 mM), 6% (0.2 mM), 15% (0.25 mM) and 26% (0.5 mM).
1 2 h L-leucine: 0.5 mM (muscle incubation) Incorporation of tyrosine (tracer) into proteins Leucine increased the specific activity of the proteins by 25% and incorporated tissue proteins by 11.5%.
27 2 h L-leucine: 0.5 mM (muscle incubation) Rate of tyrosine (tracer) incorporated and released Protein synthesis was stimulated in the soleus muscles by 69% and in EDL muscles by 38%. No effects on protein degradation were observed.
12 NR L-leucine: 5 mM (muscle incubation) Release of acid-soluble 3H-tyrosine (tracer) Leucine caused a significantly reduction in proteolysis of -8 to 12%.
11 NR L-leucine: 10 mM (muscle incubation) Rate of tyrosine (tracer) released Decreased whole-body proteolytic rate in 25%.
14 10 d L-leucine: ~0,7 g/kg/day* (ingestion) Rate of tyrosine (tracer) released Suppressed postprandial proteolysis in old rats in 40% (measured by proteasome-dependent proteolysis).
17 12–15 d BCAA: 1 g/kg/day* (ingestion) Incorporation of L- [2,6-3H]phenylalanine and release of tyrosine (tracers) Suppression on the loss of body weight (-1.5 vs. -4.5 g of control group); increase in rate of protein synthesis in gastrocnemius muscle (~50–60%) and in weight of the soleus muscle (~0.007 g); decrease of protein degradation in soleus muscle (-1500 g/2 h measured by fluorescence).
Mice
16 20 d L-leucine: ~4.2 g/day* (ingestion) Rate of incorporation of [3H]-phenylalanine and release of tyrosine (tracers) Protein synthesis was higher around 23.4% and degradation reduced in by around 11% with leucine supplementation.
Calves
18 5 d L-leucine: 239.6 μmol/L (infusion) Urea creatinine, urea nitrogen and urea 3-methyl-histidine levels Improvement on nitrogen balance without effect on protein degradation
  1. = Unpublished results; *Relativized according to the data provided; AA = amino acid; BCAA = branched-chain amino acids; KIC = [1-14C]alpha-ketoisocaproate acod; NR = Not related.