Summary
The effect of pharmacological doses of two amino acids neurotransmitters, γ-aminobutyric
acid (GABA) and β-alanine (β-Ala), on thyrotrophin (TSH) secretion was studied in
normal and hypothyroid (PTU-treated) male rats. Inhibition of TSH secretion was observed
in normal rats treated with the drugs, 30 min after their administration. Hypothyroid
animals responded only to GABA administration, decreasing their serum TSH at 30 min.
Response to thyrotrophin-releasing hormone (TRH) after 15 min of drug administration
was blunted in GABA injected animals, as compared to saline-injected controls. When
TRH was injected at the same time as GABA and β-Ala, the response was significantly
lower than in controls.
It is suggested that β-Ala and GABA act at the pituitary by impairing the TSH response
to TRH. The possibility that β-Ala actions may be due to decreased GABA catabolism
is considered, since β-Ala administration increased GABA synaptosomal levels.
Key-Words:
TSH
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TSH
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β-Alanine
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GABA
