Evidence that the branched-chain amino acid L-valine prevents exercise-induced release of 5-HT in rat hippocampus

The branched-chain amino acid L-valine competes with tryptophan for transpo rt into the brain and has previously been shown to decrease brain 5-HT synt hesis. The purpose of this study was to assess, using a combined venous cat heterization and in vivo microdialysis method, the effect of pre-exercise L -valine administration on 5-hydroxytryptamine (5-HT) metabolism in the vent ral hippocampus of rats submitted to an acute intensive treadmill running ( 120 min at 25 m x min(-1) followed by 150 min of recovery). The presented r esults include measurement of extracellular tryptophan (TRP), the 5-HT prec ursor, and extracellular 5-hydroxyindoleacetic acid (5-HIAA), the 5-HT meta bolite. The data clearly demonstrate that exercise induces 5-HT release in the rat hippocampus: in control group, hippocampal 5-HT levels increase fro m 123.7 +/- 6.4% at the end of exercise to 133.9 +/- 6.4% after 60 min of r ecovery. Moreover, two hours of intensive running induced significant incre ases both in extracellular TRP levels (from 120 min of exercise to 30 min o f recovery) and 5-HIAA levels (from 90 min of exercise to 90 min of recover y). Pre-exercise administration of L-valine prevents significantly the exer cise-induced 5-HT release: 5-HT levels are maintained to baseline during ex ercise and recovery. With regard to the competitive effect of L-valine with TRP, we could observe a treatment-induced decrease in brain TRP levels (fr om 120 min of exercise to the end of recovery). Besides, L-valine does not prevent exercise-induced increase in 5-HIAA levels. The present study evide nces that an acute intensive exercise stimulates 5-HT metabolism in the rat hippocampus, and that a pre-exercise administration of L-valine prevents, via a limiting effect on 5-HT synthesis, exercise-induced 5-HT release. Thi s study provides some anwers to previous human and animal investigations, s howing physiological and psychological benefits of branched-chain amino aci ds supplementation on performance.