Serotonin2C receptor blockade and thermoregulation during exercise in the heat.

The effect of serotonin (5-HT)2C receptor blockade on the thermal response and exercise performance during exercise in a warm environment was examined. Seven endurance-trained, but not heat-acclimatized, individuals (six males and one female) performed two 40-km time trials on a static cycle ergometer in a climatic chamber maintained at a mean (SD) ambient temperature of 35.5 (0.4) degrees C. The 5-HT2C receptor antagonist, pizotifen (1.5 mg), or placebo was administered orally on the evening before and again 6 h before exercise began. Resting rectal temperature (Tre) was higher (P=0.03) after pizotifen than placebo administration. Tre increased over time during exercise in both trials and was higher (P<0.05) during exercise in the pizotifen trial compared with the placebo trial from 40 to 60 min of exercise. There was no difference in Tre on completion of the time trial. The median times (range) required to complete the 40-km trials were 75.4 (69.0-82.5) and 76.1 (68.0-82.1) min in the pizotifen and placebo trials, respectively. Despite a trend for speed to be slower in the later stages of exercise in the pizotifen trial, performance was not significantly influenced by administration of pizotifen (P=0.86). Resting serum prolactin (Prl) and cortisol concentrations were not different after pizotifen or placebo administration. In both trials, serum Prl and cortisol values increased over time and were increased relative to resting levels in both trials (P<0.01) but were not different between treatments. The present study suggests that 5-HT may influence body temperature via an effect on the 5-HT2C receptors, but this effect was not sufficient to influence performance.