"It was initially thought that GABA ingestion increases Growth Hormone secretion, although this is true to a degree earlier studies[8] have clarified 'Growth Hormone' into a more specific subset of analogues. Immunoreactive Growth hormone (irGH) and Immunofunctional Growth Hormone (ifGH) are two analogues which appear to be elevated in vivo after oral administration of GABA.
Despite GABAs inefficacy in passing the BBB, it appears to induce these changes via neurological means, more specifically a reaction which is mediated via dopamine release at a suprapituitary level.[9]
"GABAs influence on GH secretion seems to be changed with resistance exercise. A greater overall area-under-curve and higher peak values are noted with the pairing.[10] Interestingly, the peak value with exercise occurs 30 minutes after ingestion yet 75 minutes during rest.[10] These augmenting effects may be due to exercise-induced NO potentiating GABA entry into the brain, as alluded to in the previous section.
Although it was not concluded in the previous study that the effects of GABA on growth hormone were direct (as hepatic biotransformation of GABA to other amines is a possibility), the researchers suspect it may be so.
It should be noted that Growth Hormone exists in over 100 different isoforms, and that irGH and ifGH may not exert the same benefits typically associated with the most common (22kDa) isoform of Growth Hormone.[11][12]"
References
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GABA in plasma and cerebrospinal fluid of different species. Effects of γ-acetylenic GABA, γ-vinyl GABA and sodium valproate
Transport of GABA at the Blood-CSF Interface
Al-Sarraf H Transport of 14C-gamma-aminobutyric acid into brain, cerebrospinal fluid and choroid plexus in neonatal and adult rats . Brain Res Dev Brain Res. (2002)
Efflux of a suppressive neurotransmitter, GABA, across the blood–brain barrier
Blood-brain barrier to H3-γ-aminobutyric acid in normal and amino oxyacetic acid-treated animals
Shyamaladevi N, et al Evidence that nitric oxide production increases gamma-amino butyric acid permeability of blood-brain barrier . Brain Res Bull. (2002)
Cavagnini F, et al Effect of acute and repeated administration of gamma aminobutyric acid (GABA) on growth hormone and prolactin secretion in man . Acta Endocrinol (Copenh). (1980)
Cavagnini F, et al Effect of gamma-aminobutyric acid on growth hormone and prolactin secretion in man: influence of pimozide and domperidone . J Clin Endocrinol Metab. (1980)
Powers ME, et al Growth hormone isoform responses to GABA ingestion at rest and after exercise . Med Sci Sports Exerc. (2008)
Nindl BC, et al Growth hormone molecular heterogeneity and exercise . Exerc Sport Sci Rev. (2003)
De Palo EF, et al Growth hormone isoforms, segments/fragments: does a link exist with multifunctionality . Clin Chim Acta. (2006)
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