INFLUENCE OF PAROXETINE, BRANCHED-CHAIN AMINO-ACIDS AND TYROSINE ON NEUROENDOCRINE SYSTEM RESPONSES AND FATIGUE IN HUMANS

Effects of a serotonin re-uptake inhibitor and oral amino acid supplem entations on physical and mental performance as well as neuroendocrine variables were investigated. 10 male subjects cycled in four trials u ntil exhaustion. Participants ingested a placebo in trial (T) I, 20 mg paroxetine in T II, 21 g branched-chain amino acids (BCAA) in T III a nd 20 g tyrosine (TYR) in T IV. Heart rate, capillary lactate, plasma insulin, free fatty acids, glucose, serotonin and beta-endorphine did not differ in trials. Plasma ammonia increments during exercise were h igher in T iii. Plasma BCAA in T III and plasma TYR in T IV were incre ased after 30 min of exercise according to the supplemented substances , in contrast to all other trials, the ratio of plasma free TRP/BCAA d id not increase in T III. Plasma TYR/BCAA was augmented in T IV and de creased in T III after 30 min of exercise, whereas it did not change i n T I and Il. Plasma prolactin (PRL), growth hormone, cortisol, adreno corticotropic hormone, norepinephrine and epinephrine increased during all trials. Plasma PRL increments were higher in T IV. Exhaustion was reached earlier in T Il. No significant differences were found betwee n other trials. Drive during psychometric testing subsequent to exerci se was improved in T Hi and IV The results indicate that fatigue durin g endurance exercise was increased by pharmacological augmentation of the brain serotonergic activity. However, a reduction of 5-HT synthesi s via BCAA supplementation did not affect physical fatigue. TYR admini stration did not alter physical performance either although plasma PRL increments suggest: that changes in the monoaminergic system were ind uced. Precaution is necessary before assuming an ergogenic value of am ino acids.