In Vivo Effects of γ-Aminobutyric Acid and β-Alanine on Thyrotrophin Secretion in the Normal and Hypothyroid Rat

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 - TSH - β-Alanine - GABA