Effect of Excitatory Amino Acids on Serum TSH and Thyroid Hormone Levels in Freely Moving Rats

Abstract

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.

Dose–response and histopathological study, with special attention to the hypophysis, of the differential effects of domoic acid on rats and mice

“…For instance, it has been reported that blood levels of adrenocorticotropic hormone (ACTH) were altered in naturally DA‐intoxicated sea lions ( Zalophus californianus ) (Gulland et al, ), and also that rats treated i.p. with the toxin showed an increase in thyroid‐stimulating hormone (TSH) levels in the blood (Alfonso et al, ; Arufe et al, ). Both ACTH and TSH are produced by the hypophysis, and although the variation of their parameters may be due to a plethora of causes during the intoxication episode, a putative involvement of DA in these events should be investigated thoroughly in light of the present results.…”

Effects of Dietary Threonine Levels and Stocking Density on the Performance, Metabolic Status and Immunity of Broiler Chickens

“…In rats, Alfonso et al (2001) also reported that L-Glu increased serum T3 andT4 and they suggested that the importance of EAAs in the regulation of hormone secretion from the pituitary-thyroid axis.…”

Changes in plasma thyroid hormones and cortisol levels in crucian carp (Carassius auratus) exposed to the extracted microcystins

“…Furthermore, an elevated level of cortisol, which is a common endocrine response during stress induced by waterborne pollutants, has been shown to interfere with thyroid function in fish (Walpita et al, 2007). Previous investigations demonstrate that toxins produced by some strains of phytoplankton, such as domoic acid, can alert the thyroid function of rodents by affecting neuroendocrine regulation of THs (Arufe et al, 1995;Alfonso et al, 2000). However, measurement of TH levels during MC exposure in aquatic animals has never been reported.…”