Effect of excitatory amino acids on serum TSH and thyroid hormone levels in freely moving rats.
The actions of glutamate (L-Glu), and glutamate receptor agonists on serum thyroid hormones (T4 and T3) and TSH levels have been studied in conscious and freely moving adult male rats. The excitatory amino acids (EAA), L-Glu, N-methyl-D-aspartate (NMDA), kainic acid (KA) and domoic acid (Dom) were administered intraperitoneally. Blood samples were collected through a cannula implanted in the rats jugular 0--60 min after injection. Thyroid hormone concentrations were measured by enzyme immunoassay, and thyrotrophin (TSH) concentrations were determined by radioimmunoassay. The results showed that L-Glu (20 and 25 mg/kg) and NMDA (25 mg/kg) increased serum thyroxine (T4), triiodothyronine (T3) and TSH concentrations. Serum thyroid hormone levels increased 30 min after treatment, while serum TSH levels increased 5 min after i.p. administration, in both cases serum levels remained elevated during one hour. Injection of the non-NMDA glutamatergic agonists KA (30 mg/kg) and Dom (1 mg/kg) produced an increase in serum thyroid hormones and TSH levels. These results suggest the importance of EAAs in the regulation of hormone secretion from the pituitary-thyroid axis, as well as the importance of the NMDA and non-NMDA receptors in this stimulatory effect.
Departamento de Biología Funcional y Ciencias de la Salud, Area de Fisiología, Facultad de Ciencias, Universidad de Vigo, Spain. pallares@setei.uvigo.es
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D000818:Animals; D018846:Excitatory Amino Acids / Q000494:pharmacology*; D018698:Glutamic Acid / Q000494:pharmacology; D007608:Kainic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
D018846:Excitatory Amino Acids; D014284:Triiodothyronine; D018698:Glutamic Acid; D016202:N-Methylaspartate; D013972:Thyrotropin; C012301:domoic acid; D013974:Thyroxine; D007608:Kainic Acid