Physiological inhibition of growth hormone secretion by both insulin-like growth factors-I and -II in chickens.

1. The role of both insulin-like growth factors (IGF)-I and -II in regulation of growth hormone (GH) secretion in chickens was examined. Seven-week-old male broiler chickens were injected intravenously (i.v.) with recombinant human IGF-I or IGF-II or specific anti-IGF-I or IGF-II immunoglobulins. Blood samples were taken before treatment and at 15 min intervals afterwards for 1 h. Controls received saline i.v. 2. Both IGF-I and IGF-II administration resulted in a rapid, significant decrease in plasma GH concentrations, but the concentrations of both triiodothyronine and thyroxine remained unchanged. 3. Immunisation against both IGF-I and IGF-II produced a significant elevation in plasma GH. 4. These data show that both IGFs can regulate GH concentrations in birds. Furthermore, the immunoneutralisation data suggest that these hormones have a physiological role in the regulation of GH secretion.