ENDURANCE PERFORMANCE IN HUMANS - THE EFFECT OF A DOPAMINE PRECURSOR OR A SPECIFIC SEROTONIN (5-HT2A 2C) ANTAGONIST/

In this study we examined the effect of a dopamine (DA) precursor (L-D OPA) or a serotonin (5-HT) antagonist (Ritanserin) in) on time to exha ustion. The study had a double-blind, randomised, placebo controlled a nd cross-over design. Seven moderately trained men performed three tes ts to exhaustion at 65% Watt(max). Each test was separated by two week s to allow washout of the drugs (dose: 4 mg/kg Sinemet(R), and 0.3 mg/ kg Ritanserin). Blood lactate, hematocrit, glucose, ammonia, free fatt y acids (FFA), growth hormone (GH) and catecholamines were determined before and after exercise. Time to exhaustion did not differ between t he three trials. Most of the parameters measured in this study respond ed as predicted during cycling to exhaustion in man. DA agonism signif icantly increased heart rate, lactate, and plasma DA values at rest, w hile other parameters such as FFA, lactate, plasma noradrenaline (NA) and adrenaline (A), and plasma GH showed the highest absolute levels a t exhaustion. Ritanserin did not influence basal glucose and heart rat e at rest, but this group showed a much lower increase in plasma catec holamine levels. We conclude that under the present conditions, neithe r a metabolic precursor of DA nor a specific centrally acting 5-HT2A/2 C antagonist, when given in two single doses 24 h and immediately befo re the experiments, influences the time to exhaustion on a bicycle tri al at 65% Watt(max).