The effects of branched-chain amino acid and leucine ingestion on the ERK1/2 MAP kinase signal transduction pathway in conjunction with an acute bout of heavy resistance exercise.
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Purpose: To determine if leucine or BCAA ingestion increases the activation of the ERK1/2 MAPK pathway greater than that which resistance exercise (RE) elicits alone; to determine a possible mechanism for a BCAA or leucine induced ERK1/2 MAPK pathway via IRS-1 and SHP-2. Methods: 30 males (22.5yrs; 81.1kg) were randomly assigned to 1 of 3 groups: Leucine (60mg/kg/bw), BCAA (120mg/kg/bw), or placebo. Subjects performed 4 sets of leg press and leg extension at 80% 1RM to failure. Supplementation was ingested at 3 time points: 30 minutes prior to RE, and immediately pre- and post-RE. Venous blood was sampled at baseline; 30min later, immediate post-exercise, 30min post-exercise; 2hrs post-exercise, and 6hrs post-exercise for serum glucose, insulin, GH, and IGF-1. Muscle biopsies were sampled at baseline, and 30min post, 2hr post, and 6hr post-exercise for MEK1, ERK1/2, IRS-1, and SHP-2. Skeletal muscle variables were transformed to delta values and analyzed via a 3 (group) x 4 (time points) repeated measures MANOVA. Univariate ANOVAs (Bonferroni adjusted) were conducted as follow-up tests to the MANOVA. Post-hoc tests of the interaction effects demonstrated in the ANOVA were investigated via an independent samples T-test. Results: Neither BCAA or leucine increased the secretion of the 4 serum variables. A group x time interaction relative to ERK1/2 activation indicated that the BCAA group was significantly elevated at the 2hr post and 6hr post time points in comparison with the Leucine (p < .05) and Placebo groups (p < .001). A group x time interaction for IRS-1 activation indicated that the Leucine group was significantly elevated at 2hr post and 6hr post in comparison with the BCAA (p < .05) group. No group x time interactions were observed for MEK1 or SHP-2. Summary: BCAA supplementation increased the phosphorylation status of ERK1/2 in conjunction with RE at 2 and 6 hours post-exercise. Leucine supplementation did not have any effect on ERK1/2 activation.