Insulin-like growth factors in the regulation of avian ovarian functions

In the past three decades, overwhelming evidence has accumulated to show th at insulin-like growth factor (IGF)-I and -II, their receptors and binding proteins (IGFBP) (the IGF system), have major roles to play in the regulati on of ovarian function in mammals. Although studies in birds did not start until 5-6 years ago, the limited information thus far available suggests th at the IGFs act as autocrine/paracrine regulators of follicular growth and differentiation, just as observed in mammals. The genes for IGF-I and -II, type-I IGF receptor, IGFBP-2, and IGFBP-5 are expressed in both granulosa a nd theca cells of the chicken ovary. The mechanisms by which the IGF system controls ovarian function in the avian species are complex and involve int eractions with the gonadotrophins (LH and FSH), growth hormone, and even ot her growth factors. Effects are different between strains and nutritional s tatus. (C) 1999 Elsevier Science Inc. All rights reserved.