Identification of Insulin-Like Growth Factor-Binding Protein-3 (IGFBP-3) and IGFBP-2 in Human Follicular Fluid*

Abstract

Two major insulin-like growth factor-binding proteins, IGFBP-2 and IGFBP-3, were identified by Western ligand blotting of human follicular fluid (FF) aspirated from luteinizing follicles during ovarian stimulation with human menopausal gonadotropin (LH and FSH). IGFBP-1 was also present in FF, and an IGFBP with a mol wt of 24000 daltons, present in serum, appeared to be absent in FF. Identification of IGFBP-1, IGFBP-2, and IGFBP-3 was confirmed using IGFBP-specific antisera. IGF-I and IGF-II levels were measured in patient serum and FF at the time of oocyte harvest, and serum levels of both peptides were consistently higher than FF levels. The finding of three major serum IGFBPs in human FF suggests that IGF regulation in the ovary is probably under complex control by this set of regulatory BPs.

Regulation and Physiological Role of Insulin-Like-Growth-Factor-Binding Protein-1 in Human Granulosa Cells

“…Human follicular fluid contains immunoreactive IGFBP-1 [26,27] and cultured human luteinizing granu losa cells synthesize IGFBP-1 [29,30]. Western immunoblotting in this study further suggests IGFBP-1 produc tion by human luteinizinggranulosa cells.…”

“…In humans, luteinizing granulosa cells were found to contain mRNAs encoding IGFBP-1, -2, -3, and -4 [24,25], and these four IGFBPs have been demonstrated in follicular fluid both from hyperstimulated ovarian cycles and from spontaneous cycles [26][27][28], Cultured luteiniz ing granulosa cells synthesize IGFBP-1 [29] that is con trolled by both adenylate-cyclase-and protein-kinase-Cdependent pathways [30]. IGFBP-1 inhibits IGF-I-mediated DNA amplification in human luteinizing granulo sa cells [31].…”

Insulin-Like Growth Factor-Binding Protein-1 in Human Follicular Fluid: A Marker for Oocyte Maturation

“…Giudice et al [24] observed decreased amounts of IGFBPs in immature FFs by Western ligand blotting analysis compared with that in mature FFs. Chang et al [25] reported that the fertilization rate was elevated with a high IGFBP-1 concentration in FFs.…”

Clinical Implications of Insulin-Like Growth Factors and Their Binding Proteins in Reproduction.

“…Thus, insulin excess may up-regulate hepatic production of GHBP [54]. This potential link between insulin and functional activity of the somatotropic axis is further supported by the ability of insulin excess to inhibit hepatic production of IGFBP-1, with the marked suppression of IGFBP-1 levels in obese PCOS resulting in a more than 10-fold increase in the IGF-I/IGFBP-1 ratio The follicular fluid of human ovaries has been shown to contain multiple species of IGFBPs which are thought to regulate the bioavailability of the IGFs to their target tissues [55][56][57] . There are discrete changes in IGFBP concentrations in follicular fluids which are correlated with the physiological state of the follicle [58,59].…”