REGULATION OF IGF BINDING-PROTEINS BY FSH IN HUMAN LUTEINIZING GRANULOSA-CELLS

Objectives: To evaluate the regulation of the secretion of insulin-lik e growth factor (IGF) binding proteins (IGFBPs) by FSH in human lutein izing granulosa cells. Design and Results: Luteinizing granulosa cells were incubated with and without FSH. Levels of lCFBP-1 and -3 in the medium were measured by EIA and RIA, respectively and binding activiti es of these IGFBP were evaluated by Western ligand blot. FSH inhibited the secretion of IGFBP-1 dose dependently. FSH did not inhibit the se cretion of immunoreactive IGFBP-3, but inhibited the binding activity of IGFBP-3. To assess the protease activity, I-125-IGFBP-3 was incubat ed with the cultured medium. I-125-IGFBP-3 degraded into small fragmen ts when it was incubated with the cultured medium treated with FSH. Co nclusions: FSH enhances the action of IGF-I in human granulosa cells b y inhibiting the secretion of IGFBP-1 and the binding activity of IGFB P-3 by stimulating the proteolysis of IGFBP-3.