Effect of hypophysectomy on insulin-like growth factor (IGF)-1 binding activity of serum in chickens

1. Hypophysectomy elevated IGF-1 binding activity of serum concurrently with decreases in circulating concentrations of IGF-1 and growth hormone (GH). 2. When sera pooled from each experimental group were chromatographed on a Sephadex G-200 column, IGF-1 binding activity was mainly found in 150 and 30 kilodalton (kDa) proteins. 3. Most of the serum IGF-1 were distributed among 150 kDa protein fractions. 4. Hypophysectomy elevated IGF-1 binding activity of these proteins, especially that of 30 kDa protein. 5. The binding of [125I]IGF-1 to the 30 kDa protein was inhibited by unlabelled IGF-1 but not by insulin, and saturated with a small amount of the ligand compared to the 150 kDa protein. 6. The IGF-1 binding activity of 30 kDa protein was dependent on GH status of chickens.