Effects of Thyroxine Supplement on Serum Insulin-Like Growth Factor-Binding Activity in Propylthiouracil Induced Hypothyroid Cockerels

Summary

In propylthiouracil (PTU)-fed (g/kg feed) hypothyroid cockerels, serum levels of growth hormone (GH), but not insulin-like growth factor (IGF)-1, tended to rise and those of IGF-binding activity to fall. Thyroxine (T₄) supplement (200 μg/kg/day) to PTU-fed cockerels for 8 days produced a hyperthyroid state and reversed these serum parameters. A chromatographic analysis of serum proteins revealed that T₄ supplement markedly enhanced the IGF-binding activity of a 30 kDa protein and slightly lowered that of a 150 kDa protein, suggesting that T₄ increases unsaturated IGF-binding proteins by reducing circulating IGF-1 concentrations.

Key words

Chicken - Hypothyroid - Thyroxine - IGF-Binding Proteins