Oral administration of γ-aminobutyric acid affects heat production in a hot environment in resting humans

Background: Central administration of gamma-amino butyric acid (GABA) induces lower body temperature in animals in hot ambient air. However, it is still unknown whether oral GABA administration affects temperature regulation at rest in a hot environment in humans. Therefore, in the present study, we specifically hypothesized that systemic administration of GABA in humans would induce hypothermia in a hot environment and that this response would be observed in association with decreased heat production. Methods: Eight male participants drank a 200-ml sports drink with 1 g of GABA (trial G) or without GABA (trial C), then rested for 30 minutes in a sitting position in a hot environment (ambient air temperature 33 degrees C, relative humidity 50%). Results: We found that changes in esophageal temperature from before drinking the sports drink were lower in trial G than in trial C (-0.046 +/- 0.079 degrees C vs 0.001 +/- 0.063 degrees C; P < 0.05), with lower heat production calculated by oxygen consumption (41 +/- 5 W/m(2) vs 47 +/- 8 W/m(2); P < 0.05). Conclusions: In this study, we have demonstrated that a single oral administration of GABA induced a larger decrease in body core temperature compared to a control condition during rest in a hot environment and that this response was concomitant with a decrease in total heat production.