Effects Of Oral Administration Of Gamma-aminobutyric Acid On Body Temperature Regulation In Human During Exercise In A High-temperature Environment

Objective: Gamma-aminobutyric acid (GABA), is the major inhibitory neurotransmitter in thebrain, that may play important roles in thermoregulation. Central administration of GABA hassome effects on body temperature regulation in animals. However, it is unknown whether oraladministration of GABA affects body temperature regulation during exercise in high-temperatureenvironments in human. The purpose of this study was to examine the effects of oraladministration of GABA on body temperature regulation in human during prolonged exercise ina high-temperature environment for providing the basis of controlling core body temperature intraining and competition.Methods: This study used experimental method with a double-blind randomized crossoverdesign. Eighteen male endurance collegiate athletes (age:21.17±1.24years,V o2max:62.11±6.72mL/kg/min) volunteered to participate this study. Each subject completedtwo trials that exercise at60%maximal workload (1.98±0.25kp) for40minutes on a cycleergometer at a pedaling cadence of60rmp. In each of the experiment, subject rested20minutesat pre-exercise, and recovered20minutes at post-exercise. In the GABA exercise trial (trial-G),subjects drank a sports drink (3ml/kg body mass) containing1000mg GABA, while in thecontrol exercise trial (trial-C) subjects drank the same amount of sports drink. During theexperiments, rectum temperature (core body temperature), skin temperatures (including arm,chest, thigh and leg), heart rate, and rate of perceived exertion (RPE) were continuouslymeasured. Mean skin temperature was calculated.Results:(1) In the trial-G and the trial-C, core body temperatures showed an increase tendency during theexercise and a decrease tendency during the recovery (All P<0.01). Core body temperaturesin the trial-G during the rest and recovery were significantly higher than those in the trial-C.The differences of core body temperatures in the trial-G during the exercise weresignificantly lower than those in the trial-C, however, the differences in the trial-G during therest and recovery were significantly higher than those in the trial-C (All P<0.01).(2) In the trial-G and the trial-C, mean skin temperature showed an increase tendency duringthe exercise and a decrease tendency during the recovery (All P<0.05). Mean skintemperatures in the trial-G during the rest, the post-exercise15-40minutes, and the recoverywere significantly higher than those in the trial-C. The differences of mean skin temperatures in the trial-G during the post-exercise20-40minutes and the recovery were significantlyhigher than those in the trial-C (All P<0.05).(3) The differences of heart rates during the40minutes exercise period and the recovery in thetrial-G were significantly higher compared with those of in trial-C (All P<0.05).(4) In the trial-G and the trial-C, the percentage of body mass loss were1.03±0.19%and1.05±0.18%respectively； The maximum heart rates were173.89±12.56beats/min and174.33±9.89beats/min respectively； The maximum blood lactate concentration were3.96±1.52mmol/L and3.67±1.70mmol/L； The maximum RPE were13.39±2.70and13.44±2.71. The differences of these measurements between the two experimental conditionsshowed no statistical significance (All P>0.05).Conclusions:(1) Oral administration of GABA affects body temperature regulation in human during exercisein the high-temperature environment. Orally administrated GABA contributes to inhibit theincrease in core body temperature and promote heat dissipation by skin.(2) Oral administration of GABA increases heart rate in human during exercise in thehigh-temperature environment. By increasing the flow of blood to the skin that augmentseffect of skin heat dissipation.(3) Oral administration of GABA in the high-temperature environment makes a remarkableincrease in core body temperatures post exercise. In this case there is a danger of serioushyperthermia that should be pay more attention.