Guy De Schutter

The effects of acute dopamine reuptake inhibition on performance.

INTRODUCTION Acute bupropion (dopamine/noradrenaline reuptake inhibitor) administration significantly improved time trial performance and increased core temperature in the heat (30 degrees C). PURPOSE The present study was performed to examine the effect of a dopaminergic reuptake inhibitor on exercise capacity and thermoregulation during prolonged exercise in temperate and warm conditions. METHODS Eight healthy well-trained male cyclists participated in this study. Subjects ingested either placebo (PLA; 20 mg) or methylphenidate (MPH; Ritalin; 20 mg) 1 h before the start of exercise in temperate (18 degrees C) or warm (30 degrees C) conditions and cycled for 60 min at 55% Wmax, immediately followed by a time trial (TT; PLA18 and MPH18; PLA30 and MPH30) to measure exercise performance. RESULTS MPH did not influence TT performance at 18 degrees C (P = 0.397). TT was completed 16% faster in MPH30 (38.1 +/- 6.4 min) than in PLA30 (45.4 +/- 7.3 min; P = 0.049). In the heat Tcore was significantly higher at rest (P = 0.009), and throughout the TT in MPH30 (P < 0.018), reaching values above 40 degrees C. Throughout MPH30, heart rates were significantly higher (P < 0.05). CONCLUSIONS These results show that MPH has a clear ergogenic effect that was not apparent in 18 degrees C. The combination of a dopamine reuptake inhibitor and exercise in the heat clearly improved performance and caused hyperthermia without any change in the perception of effort or thermal stress compared with the PLA trial. This response may potentially increase the risk of developing heat illness during exercise in individuals taking drugs of this nature.

Acute norepinephrine reuptake inhibition decreases performance in normal and high ambient temperature

Combined inhibition of dopamine (DA)/norepinephrine (NE) reuptake improves exercise performance and increases core temperature in the heat. A recent study demonstrated that this effect may primarily be related to increased DA activity. NE reuptake inhibition (NERI), however, has received little attention in humans, certainly in the heat, where central fatigue appears to be a main factor influencing performance. Therefore the present study examines the effect of NERI (reboxetine) on exercise capacity, thermoregulation, and hormonal response in normal and high temperature. Nine healthy well-trained male cyclists participated in this study. Subjects ingested either placebo (Pla; 2 x 8 mg) or reboxetine (Rebox; 2 x 8 mg). Subjects exercised in temperate (18 degrees C) or warm (30 degrees C) conditions and cycled for 60 min at 55% W(max) immediately followed by a time trial (TT; Pla18/Rebox18; Pla30/Rebox30) to measure exercise performance. Acute NERI decreased power output and consequently exercise performance in temperate (P = 0.018) and warm (P = 0.007) conditions. Resting heart rate was significantly elevated by NERI (18 degrees C: P = 0.02; 30 degrees C: P = 0.018). In Rebox18, heart rate was significantly higher than in the Pla18, while in the heat no effect of the drug treatment was reported during exercise. In Rebox30, all hormone concentrations increased during exercise, except for growth hormone (GH), which was significantly lower during exercise. In Rebox18, prolactin (PRL) concentrations were significantly elevated; GH was significantly higher at rest, but significantly lower during exercise. In conclusion, manipulation of the NE system decreases performance and modifies hormone concentrations, thereby indicating a central NE effect of the drug. These findings confirm results from previous studies that predominantly increased DA activity is important in improving performance.

No effect of a noradrenergic reuptake inhibitor on performance in trained cyclists

INTRODUCTION According to the central fatigue hypothesis, serotonin (5-HT) is related to fatigue, whereas the noradrenergic system is primarily concerned with arousal and motivation, and therefore hypothesized to enhance performance. The purpose of the present study was to examine the effects of a selective noradrenergic reuptake inhibitor (reboxetine 2 x 4 mg REB-NARI) on exercise performance. METHODS Seven healthy well-trained male cyclists (age: 23 +/- 1.7 yr, height: 182 +/- 5.8 cm, weight: 73.5 +/- 8.5 kg, VO2max: 73.5 +/- 6.4 mL x kg(-1) x min(-1), Watt(max): 376 +/- 11.7 W) participated to the study. Subjects completed two endurance tests (time trials) starting at 65% Wmax in a double-blind randomized cross-over design. Blood samples were collected for adrenocorticotropin, prolactin, cortisol, growth hormone (GH), beta-endorphins, and catecholamines and were taken at 30-min time intervals until the end of exercise. Performance was analyzed with a paired t-test, whereas data for hormonal and metabolic differences during the trials were analyzed using an ANOVA repeated measures design and an LSD-planned comparisons test. Significance level was set at P < 0.05. RESULTS Performance was not influenced by the NARI (REB: 97 min +/- 3 min, placebo (PLAC): 92 min +/- 1 min). All hormones increased during exercise except for GH in the REB trial, which was significantly lower than PLAC. The other hormones were significantly higher in the REB trial versus the PLAC trial at the end of exercise and during recovery. CONCLUSION In conclusion, the results demonstrate that the drug had a central effect. In particular, the higher resting GH concentrations indicated a marked and selective noradrenergic effect of REB. However, performance was not influenced by a selective NARI in well-trained endurance athletes.

No Effect of a Selective Serotonergic/Noradrenergic Reuptake Inhibitor on Endurance Performance

The purpose of the present study was to examine the effects of a selective serotonin/noradrenaline (5-HT/NA) reuptake inhibitor (SNRI) on exercise performance. Seven well-trained male cyclists completed 2 time trials in a doubleblind randomized crossover design ingesting either placebo (PLAC) or 2 × 37.5 mg of Venlafaxine (VEN). Blood samples were collected for adrenocorticotropin hormone (ACTH), prolactin (PRL), cortisol, growth hormone (GH), beta-endorphins, and catecholamines and were taken at rest, at 30-min time intervals, at the end of exercise, and during recovery. Performance was not influenced by the SNRI (VEN: 92 min ± 3 min, PLAC: 92 min ± 1 min). Lactate concentrations, heart rate, and fatigue scores were not different between trials. All hormones increased during exercise in both trials. In the VEN trial, ACTH, beta endorphins, and NA concentrations were higher. The results from the present study demonstrate that a SNRI is not able to affect endurance performance in well-trained cyclists. However, it seems as though the hormonal response to the combination of the pharmacological manipulation and exercise is regulated more by the noradrenergic drive.