RESEARCH PAPER Temperature 1:3, 242--247; October/November/December 2014; Published with license by Taylor & Francis Group, LLC
The ergogenic effect of amphetamine Dmitry V Zaretsky1, Mary Beth Brown2, Maria V Zaretskaia1, Pamela J Durant1, and Daniel E Rusyniak1,3,* 1
Department of Emergency Medicine; Indiana University School of Medicine; Indianapolis, IN USA; 2Department of Physical Therapy; Indiana University School of Health and Rehabilitation Sciences; Indianapolis, IN USA; 3Department of Pharmacology and Toxicology; Indiana University School of Medicine; Indianapolis, IN USA
Keywords: amphetamine, exhaustion, exertional heat stroke, running economy, VO2Max Abbreviations: Amp, amphetamine; VO2Max, maximum oxygen consumption; W, watt; ANOVA, analysis of variance; LSD, least squares difference; iBAT, interscapular brown adipose tissue; VTA, ventral tegmental area
Amphetamine (Amp) increases exercise duration. It is thought to do so by masking fatigue, but there have been very few studies looking at the effect of amphetamine on maximal oxygen consumption (VO2MAX) and running economy. Furthermore, it is unknown if amphetamine’s effect on exercise duration occurs in a warm environment. We conducted separate experiments in male Sprague-Dawley rats testing the effect of amphetamine on VO2MAX (n D 12), running economy (n D 12), and exercise duration (n D 24) in a warm environment. For VO2MAX and running economy, rats were randomized to either amphetamine at 1 mg/kg (Amp-1) or 2 mg/kg (Amp-2). Animals served as their own controls in a crossover design with the administration order counter-balanced. To study the effect of amphetamine on exercise duration, we conducted run-to-exhaustion treadmill testing on rats in a 328C environment following administration of Amp-1, Amp-2, or Saline. Compared to control, Amp-2 increased VO2MAX (by 861 § 184 ml/kg/hr, p D 0.005) and the time to VO2MAX (by 2.5 § 0.8 min, p D 0.03). Amp-1 had no effect on VO2MAX but increased the time to VO2MAX (by 1.7 § 0.5 min, p D 0.03). Neither dose improved running economy. In the warm, only rats in the Amp-1 group (C9.4 min, p D 0.02) had an increased time to exhaustion. Compared to control (41.6 § 0.3 C), both amphetamine doses had higher temperatures at exhaustion: Amp-1 (42.0 § 0.2 C) and Amp-2 (42.1 § 0.2 C). Our results suggest that ergogenic effect of amphetamine occurs by masking fatigue but this effect may be offset in the warm with higher doses.
Introduction “ The man who can drive himself farther once the effort gets painful will win” - Roger Bannister While the media focuses predominantly on the illegal use of anabolic steroids and blood doping in sports, stimulants like amphetamines are still widely used in competition.1 In 2013, the World Anti-Doping Agency listed stimulants as the second most detected banned substance. Previous research has shown that amphetamine (Amp) improves exercise endurance.2-4How it does this is not known. It is largely thought to occur by masking the perception of fatigue.2-7 However, there have only been a few studies looking at peripheral mechanisms such as increasing oxygen utilization. In one study, a relatively small dose of Amp (»0.2 mg/kg) was given to 6 volunteers. While the time to exhaustion was increased, the VO2MAX was not affected.3 A similar study in 2 volunteers given a low dose of methamphetamine also showed no effect on VO2MAX but an increase in exercise endurance.7 Independent of exercise, amphetamines are known to increase body temperature by increasing heat production while
simultaneously decreasing heat dissipation.8,9 As body temperature is a key factor in limiting the duration of exercise,10 it is possible that any ergogenic advantages offered by amphetamines when used in a cool environment would be offset if used in the warm. Amphetamines effect on athletic performance in the warm has not however been evaluated. Amphetamine is also known to improve exercise endurance in rats.5,11,12 There are no studies, however, in rats measuring the effect of higher doses of Amp on exercise-related VO2MAX or the effect of Amp on exercise endurance in the heat. Therefore, we sought to determine the effect of 2 doses of Amp on VO2MAX and running economy in rats at room temperature. Furthermore we tested if Amp increased running time in the heat and if so what affect this had on core body temperature.
Methods Animals Male adult Sprague-Dawley rats (weight 300 § 20 g; Harlan, Indianapolis, IN) were used in this study. All procedures were
© Dmitry V Zaretsky, Mary Beth Brown, Maria V Zaretskaia, Pamela J Durant, and Daniel E Rusyniak *Correspondence to: Daniel E Rusyniak; Email: [email protected] Submitted: 11/10/2014; Accepted: 11/10/2014 http://dx.doi.org/10.4161/23328940.2014.987564 This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The moral rights of the named author(s) have been asserted.
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approved by the Indiana University Animal Care and Use Committee. Experiments were performed using single-housed rats that were maintained in a 12 h light/dark cycle and fed ad libitum. Experiments were conducted on fully conscious rats between 10:00 a.m. and 4:00 p.m. in a temperature-controlled room or in a specially designed environmental chamber. Chemicals d-Amphetamine was purchased from Sigma (Sigma-Aldrich, St. Louis, MO) and dissolved in sterile saline (0.9%) to a volume of 1 ml/kg of body weight. Surgical preparation Animals were anesthetized with 1.5–2% isoflurane in oxygen. For the measurement of core body temperature, TA-F40 telemetric transmitters (DSI, St. Paul, MN) were placed intraperitoneally (i.p.) via a 2 cm-long longitudinal medial skin incision and muscular wall incision at the linea alba. Following insertion of the transmitter into the abdominal cavity and surgical closure, rats were returned to their cage for at least 1 week before beginning treadmill familiarization. Treadmill familiarization Prior to experiments, rats were familiarized to running on a motorized rodent treadmill (Columbus Instruments, Columbus, OH) using one of 2 schedules, depending on the experiments to follow. To prepare rats for experiments that utilized an incremental treadmill protocol, such as for measurement of maximal rate of oxygen uptake (VO2Max), a 14-day familiarization protocol was used. Rats were run on the treadmill for 5 min/day with both the slope and speeds increasing daily; for example, on day one rats were run at a 5 incline at a maximum speed of 10 m/min and by day 15 at an incline of 20 and a maximum speed of 26 m/min. To prepare rats for experiments that utilized a fixed-speed protocol, such as those for measurement of time to exhaustion and running economy, a simpler 5-day familiarization program was used with a fixed incline at 5 and the speed increased progressively to a maximum of 18 m/min by day 5. Workloads of familiarization schedules accustom the rats to treadmill running, but are not sufficient to induce training adaptations.13 Mild electric stimulus at the back of the treadmill chamber promoted learned running behavior. Any animal that was unable to consistently run at the front of the treadmill by the end of the familiarization sessions was eliminated from the study. In all of the experiments a motorized fan on the front of the treadmill circulated fresh air into the chamber. Temperature chamber We constructed an environmental chamber to conduct experiments at elevated temperatures. The walls were made of 1=4 ” Plexiglas covered with 3/4” Styrofoam with the following internal dimensions 55’(w) £ 35’(d) £ 27’(h). A door in the front of the chamber was large enough to move the treadmill in and out. The motor of the treadmill outside the box and was connected to the lanes with a 1.5 m long shaft through the hole in the wall of chamber. To circulate air in the box we installed 2 90£90 mm fans operated at 1800 rpm (low noise computer case fans).
www.landesbioscience.com
Heating was produced using a 600 W ceramic heater and the temperature was regulated with an electronic single-stage temperature controller (model111000–000, Ranco, Plain City, OH). The temperature controller thermistor was positioned next to the lane of the treadmill (or between lanes if 2 were present inside the environmental chamber), with the thermistor’s coating stripped off to increase its time constant of response. For experiments conducted at elevated temperature, the chamber temp was set at 32 § 1 C and humidity
The ergogenic effect of amphetamine Dmitry V Zaretsky1, Mary Beth Brown2, Maria V Zaretskaia1, Pamela J Durant1, and Daniel E Rusyniak1,3,* 1
Department of Emergency Medicine; Indiana University School of Medicine; Indianapolis, IN USA; 2Department of Physical Therapy; Indiana University School of Health and Rehabilitation Sciences; Indianapolis, IN USA; 3Department of Pharmacology and Toxicology; Indiana University School of Medicine; Indianapolis, IN USA
Keywords: amphetamine, exhaustion, exertional heat stroke, running economy, VO2Max Abbreviations: Amp, amphetamine; VO2Max, maximum oxygen consumption; W, watt; ANOVA, analysis of variance; LSD, least squares difference; iBAT, interscapular brown adipose tissue; VTA, ventral tegmental area
Amphetamine (Amp) increases exercise duration. It is thought to do so by masking fatigue, but there have been very few studies looking at the effect of amphetamine on maximal oxygen consumption (VO2MAX) and running economy. Furthermore, it is unknown if amphetamine’s effect on exercise duration occurs in a warm environment. We conducted separate experiments in male Sprague-Dawley rats testing the effect of amphetamine on VO2MAX (n D 12), running economy (n D 12), and exercise duration (n D 24) in a warm environment. For VO2MAX and running economy, rats were randomized to either amphetamine at 1 mg/kg (Amp-1) or 2 mg/kg (Amp-2). Animals served as their own controls in a crossover design with the administration order counter-balanced. To study the effect of amphetamine on exercise duration, we conducted run-to-exhaustion treadmill testing on rats in a 328C environment following administration of Amp-1, Amp-2, or Saline. Compared to control, Amp-2 increased VO2MAX (by 861 § 184 ml/kg/hr, p D 0.005) and the time to VO2MAX (by 2.5 § 0.8 min, p D 0.03). Amp-1 had no effect on VO2MAX but increased the time to VO2MAX (by 1.7 § 0.5 min, p D 0.03). Neither dose improved running economy. In the warm, only rats in the Amp-1 group (C9.4 min, p D 0.02) had an increased time to exhaustion. Compared to control (41.6 § 0.3 C), both amphetamine doses had higher temperatures at exhaustion: Amp-1 (42.0 § 0.2 C) and Amp-2 (42.1 § 0.2 C). Our results suggest that ergogenic effect of amphetamine occurs by masking fatigue but this effect may be offset in the warm with higher doses.
Introduction “ The man who can drive himself farther once the effort gets painful will win” - Roger Bannister While the media focuses predominantly on the illegal use of anabolic steroids and blood doping in sports, stimulants like amphetamines are still widely used in competition.1 In 2013, the World Anti-Doping Agency listed stimulants as the second most detected banned substance. Previous research has shown that amphetamine (Amp) improves exercise endurance.2-4How it does this is not known. It is largely thought to occur by masking the perception of fatigue.2-7 However, there have only been a few studies looking at peripheral mechanisms such as increasing oxygen utilization. In one study, a relatively small dose of Amp (»0.2 mg/kg) was given to 6 volunteers. While the time to exhaustion was increased, the VO2MAX was not affected.3 A similar study in 2 volunteers given a low dose of methamphetamine also showed no effect on VO2MAX but an increase in exercise endurance.7 Independent of exercise, amphetamines are known to increase body temperature by increasing heat production while
simultaneously decreasing heat dissipation.8,9 As body temperature is a key factor in limiting the duration of exercise,10 it is possible that any ergogenic advantages offered by amphetamines when used in a cool environment would be offset if used in the warm. Amphetamines effect on athletic performance in the warm has not however been evaluated. Amphetamine is also known to improve exercise endurance in rats.5,11,12 There are no studies, however, in rats measuring the effect of higher doses of Amp on exercise-related VO2MAX or the effect of Amp on exercise endurance in the heat. Therefore, we sought to determine the effect of 2 doses of Amp on VO2MAX and running economy in rats at room temperature. Furthermore we tested if Amp increased running time in the heat and if so what affect this had on core body temperature.
Methods Animals Male adult Sprague-Dawley rats (weight 300 § 20 g; Harlan, Indianapolis, IN) were used in this study. All procedures were
© Dmitry V Zaretsky, Mary Beth Brown, Maria V Zaretskaia, Pamela J Durant, and Daniel E Rusyniak *Correspondence to: Daniel E Rusyniak; Email: [email protected] Submitted: 11/10/2014; Accepted: 11/10/2014 http://dx.doi.org/10.4161/23328940.2014.987564 This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The moral rights of the named author(s) have been asserted.
242
Temperature
Volume 1 Issue 3
approved by the Indiana University Animal Care and Use Committee. Experiments were performed using single-housed rats that were maintained in a 12 h light/dark cycle and fed ad libitum. Experiments were conducted on fully conscious rats between 10:00 a.m. and 4:00 p.m. in a temperature-controlled room or in a specially designed environmental chamber. Chemicals d-Amphetamine was purchased from Sigma (Sigma-Aldrich, St. Louis, MO) and dissolved in sterile saline (0.9%) to a volume of 1 ml/kg of body weight. Surgical preparation Animals were anesthetized with 1.5–2% isoflurane in oxygen. For the measurement of core body temperature, TA-F40 telemetric transmitters (DSI, St. Paul, MN) were placed intraperitoneally (i.p.) via a 2 cm-long longitudinal medial skin incision and muscular wall incision at the linea alba. Following insertion of the transmitter into the abdominal cavity and surgical closure, rats were returned to their cage for at least 1 week before beginning treadmill familiarization. Treadmill familiarization Prior to experiments, rats were familiarized to running on a motorized rodent treadmill (Columbus Instruments, Columbus, OH) using one of 2 schedules, depending on the experiments to follow. To prepare rats for experiments that utilized an incremental treadmill protocol, such as for measurement of maximal rate of oxygen uptake (VO2Max), a 14-day familiarization protocol was used. Rats were run on the treadmill for 5 min/day with both the slope and speeds increasing daily; for example, on day one rats were run at a 5 incline at a maximum speed of 10 m/min and by day 15 at an incline of 20 and a maximum speed of 26 m/min. To prepare rats for experiments that utilized a fixed-speed protocol, such as those for measurement of time to exhaustion and running economy, a simpler 5-day familiarization program was used with a fixed incline at 5 and the speed increased progressively to a maximum of 18 m/min by day 5. Workloads of familiarization schedules accustom the rats to treadmill running, but are not sufficient to induce training adaptations.13 Mild electric stimulus at the back of the treadmill chamber promoted learned running behavior. Any animal that was unable to consistently run at the front of the treadmill by the end of the familiarization sessions was eliminated from the study. In all of the experiments a motorized fan on the front of the treadmill circulated fresh air into the chamber. Temperature chamber We constructed an environmental chamber to conduct experiments at elevated temperatures. The walls were made of 1=4 ” Plexiglas covered with 3/4” Styrofoam with the following internal dimensions 55’(w) £ 35’(d) £ 27’(h). A door in the front of the chamber was large enough to move the treadmill in and out. The motor of the treadmill outside the box and was connected to the lanes with a 1.5 m long shaft through the hole in the wall of chamber. To circulate air in the box we installed 2 90£90 mm fans operated at 1800 rpm (low noise computer case fans).
www.landesbioscience.com
Heating was produced using a 600 W ceramic heater and the temperature was regulated with an electronic single-stage temperature controller (model111000–000, Ranco, Plain City, OH). The temperature controller thermistor was positioned next to the lane of the treadmill (or between lanes if 2 were present inside the environmental chamber), with the thermistor’s coating stripped off to increase its time constant of response. For experiments conducted at elevated temperature, the chamber temp was set at 32 § 1 C and humidity
