The Importance Of Leucine In Stimulating Protein Signaling After Resistance Exercise In Young Females
Marcus Borgenvik Medicine & Science in Sports & Exercise. 2012 44(5S): p 444
Essential amino acids (EAA) and resistance exercise are well-documented in their capacity to stimulate human muscle protein. Out of the EAA, leucine has been proposed to have a unique role
in promoting proteinsynthesis through activation of the mammalian target of rapamycin (mTOR) pathway.
PURPOSE: To evaluate the role of leucine with regard to mTOR signaling and mRNA expression of possible regulators of mTOR in young females following resistance exercise.
METHODS: Eight healthy females performed two sessions of leg press exercise and were randomly supplied a mixture of EAA with or without leucine (EAA-Leu). Blood samples were
taken repeatedly throughout the experiment and muscle biopsy samples were collected before, 1h, and 3h after resistance exercise and analyzed for phosphorylation status of proteins in the
mTOR pathway and mRNA expression of mTOR-associated genes. In addition, levels of free amino acids were determined plasma and muscle samples.
RESULTS: The phosphorylation of mTOR at Ser2448 was elevated ~2-fold above baseline at 1h and 3h post exercise with both supplements (P<0.05). During EAA supplementation the
phosphorylation of p70S6K at Thr389 was 30-fold higher than at baseline and 5-fold higher than EAA-Leu (P<0.05) 1h post exercise. The mRNA expression of Rheb increased ~ 1.7 fold and that
of Redd1 decreased ~ 60 % 3h post exercise (P<0.05), with no differences between supplements. The plasma levels of isoleucine, valine, methionine, tryptophan and tyrosine were all 16 to 58
% lower after EAA than EAA-Leu following 2 and 3h of recovery (P<0.05). At 3h after exercise muscle levels of these amino acids were 28 to 59 % lower when leucine was present in the
drink (P<0.05). In addition, in the EAA trial muscle levels of leucine increased 64 and 32 % while in the EAA-Leu trial a 44 and 39 % reduction was observed 1 and 3h post exercise,
respectively.
CONCLUSION: The significantly higher response with regard to p70S6K phosphorylation in the presence of leucine emphasizes its importance in the activation of enzymes in the mTOR pathway.
In addition, the larger reduction of essential amino acids in plasma and muscle provide further support for a specific role of leucine in stimulating protein synthesis.
