Diminished central fatigue by inhibition of the L-system transporter for the uptake of tryptophan

Nagase genetically analbuminemic rats (NAR) were run to fatigue. Administra tion of branched chain amino acids (BCAA) before exhaustive exercise, resul ted in a post-fatigue decreased tryptophan uptake (-22%, p < 0.05) and 5-hy droxytryptophan (5-HTP) uptake (-29%, p < 0.01) into the synaptosomes isola ted from the striatum when compared with saline administration. At the same time, NAR who received either BCAA or 2-aminobicyclo[2,2,1]heptane-2-carbo xylic acid (BCH, a specific inhibitor for the L-system transporter) had a c onsiderably prolonged run time to exhaustion (by twofold), compared to thos e who received either saline or albumin treatments. When classified by run time, it was of interest that, when the data for BCAA and BCH treatments fo r the longer run time NAR (Group B) was combined, it gave rise to a signifi cant decrease in synaptosomal tryptophan and 5-HTP of a similar magnitude t o that observed with BCAA alone. These levels were lower than those observe d in NAR in the shorter run time group (Group A) for all treatments. These results support the view that an activated serotonergic function may be inv olved in central fatigue, which can be diminished by inhibition of the L-sy stem transporter. (C) 2000 Elsevier Science Inc.