THE EFFECTS OF GAMMA AMINOBUTYRIC ACID ON GROWTH HORMONE SECRETION AT REST AND FOLLOWING EXERCISE

Gamma aminobutyric acid (GABA) is a neurotransmitter that plays a key role in growth hormone (GH) secretion. GABA is manufactured and sold as an ergogenic aid with the claim that GH secretion will increase following ingestion. PURPOSE To examine the GH and immunofunctional GH (IFGH) response to GABA ingestion during resting and exercise conditions. METHODS Seven resistance trained males (21.33±1.28 yrs, 176.75±4.07 cm, 81.12±10.63 kg) participated in four randomly ordered testing conditions; rest following placebo ingestion, rest following GABA ingestion, exercise following placebo ingestion, and exercise following GABA ingestion. Subjects ingested capsules containing either 3-g of GABA or a sucrose placebo after initial venous blood samples were taken. During the resting conditions, the subjects remained in a reclined position while blood samples were taken every 15-min for a total of 90-min following ingestion. During the exercise conditions, each subject performed a resistance exercise protocol immediately following ingestion. This consisted of a single set to failure with 70% of a previously determined 1-RM for 11 different exercises separated by a 1-min rest period. Blood samples were again taken immediately following exercise and every 15-min during a 90-min recovery period. ELISA was performed to determine serum levels of GH and IFGH. RESULTS GABA ingestion had no effect on resting levels of GH and IFGH. A significant increase in GH [F(6,36)=.3.32, p = .010] was observed following exercise with a greater increase observed when GABA was ingested. GH levels were significantly greater following GABA ingestion, as compared to placebo ingestion, 15- and 30-min post exercise. A significant increase in IFGH was also observed following exercise [F(6,36)=2.76, p = .026], however GABA ingestion did not have an effect on this measure. CONCLUSION While no changes were observed in a resting state, the results of this study partially support claims that GABA increases GH secretion, as greater levels of GH were observed following exercise when GABA was ingested.