Endogenous Insulin-Like Growth Factor-I Is Obligatory for Stimulation of Rat Inhibin α-Subunit Expression by Follicle-Stimulating Hormone1

Insulin-like growth factor-I (IGF-I) is essential for FSH-dependent steroidogenesis by rat granulosa cells (GC), but whether IGF-I is required for other FSH-dependent functions is unknown. To investigate the role of IGF-I in the mechanisms of FSH-stimulated inhibin α-subunit (Inh-α) production, rat GC were cultured with FSH, IGF-I, insulin-like growth factor-binding protein (IGFBP)-4, IGFBP-5, and/or anti-IGF-I antibody. Inh-α protein and mRNA...