Effects of Glucocorticoids on Circulating Concentrations of Thyroxine (T₄) and Triiodothyronine (T₃) and on Peripheral Monodeiodination in Pre- and Post-Hatching Chickens

Summary

The administration of either glucocorticoids (dexamethasone or corticosterone) or adrenocorticotropic hormone (ACTH) to chicken embryos was followed by increase in the circulating concentration of triiodothyronine (T₃), the T₃ to thyroxine (T₄) ratio and the activity of liver T₄-5′ monodeiodinase. No consistent changes in plasma concentrations of T₄ or GH were observed. In post-hatching chicks, corticosterone and dexamethasone depressed the circulating concentrations of both T₄ and T₃. Iopanic acid, an inhibitor of liver T₄-5′ monodeiodinase, elevated plasma concentrations of T₄ and depressed those of T₃, in both chicken embryos and young chicks. It is suggested that glucocorticoids affect circulating concentrations of T₄ and T₃ both by affecting the activity of the liver T₄-5′ monodeiodinase and by influencing the hypothalamo-pituitary axis.

Key-Words:

Glucocorticoids - Circulating Thyroxine (T₄) and Triiodothyroxine (T₃) - Liver T₄-5′ Monodeiodinase - Chickens