Title: Regulation of thyroid hormone availability in liver and brain by glucocorticoids
Abstract: Glucocorticoids as well as thyroid hormones are essential for normal brain development. Exogenous glucocorticoids stimulate 3,3′,5-triiodothyronine (T3) availability in circulation of birds and similar effects have been observed in sheep. Chicken data indicate that glucocorticoid administration also stimulates thyroid hormone metabolism in brain but the effects on local thyroid hormone concentrations are not known. Therefore, the current study: (1) determined local thyroid hormone availability in separate brain areas of 18-day-old embryonic chickens (E18) after injection of dexamethasone (DEX), and (2) investigated the impact on the thyroid hormone metabolic pathways in these brain parts and compared the results with the hepatic situation. For this, E18 chicken embryos were treated with a single intravenous dose of DEX (25 μg). Despite the decreased 3,5,3′,5-tetraiodothyronine (T4) availability in the liver of the DEX treated embryos, the T3 content was strongly increased, parallel to the plasma T3 surge. This T3 surge was primarily related to a fall in hepatic T3 breakdown through a downregulation of the type III deiodinase (D3). The sulfation pathway in liver seems not to be affected by DEX. In all brain parts, DEX affects the T3 production capacity by upregulation of the type II deiodinase (D2). This enables the brain to compensate for the decrease in T4 availability, although the T3 concentrations are not consistently increased like in plasma and liver. This observation points to the existence of a fine-tuning mechanism in brain that enables the brain to keep the T3 concentrations within narrow limits.
Publication Year: 2005
Publication Date: 2005-01-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
Access and Citation
Cited By Count: 28
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