Insulin-like growth factor binding protein profiles in human ovarian follicular fluid correlate with follicular functional status

Abstract

The insulin-like growth factors (IGF), IGF-I and IGF-II, influence ovarian follicular development. The IGF binding proteins (IGFBPs) comprise at least six distinct species which may modulate IGF action. We examined IGFBP profiles in follicular fluid (FF) from developing human ovarian follicles with aromatase activity as well as from androgen-dominant, atretic follicles. Western ligand blot analysis of FF from both atretic and active follicles revealed the presence of IGFBP-3 and IGFBP-2, confirmed by immunoprecipitation with specific antiserum, as well as 28 kilodalton (kDa) and 24 kDa IGFBPs. In FF specimens obtained during the follicular phase, IGFBP-2 and the 28 kDa and 24 kDa species were present in 3-, 6-, and 19-fold higher amounts in atretic compared to healthy developing follicles, respectively, and were present in greater amounts in atretic FF than in serum. In atretic FF obtained during the luteal phase, lower levels of IGFBP-2 and the 28 and 24 kDa IGFBPs were seen than in atretic follicles in the follicular phase. IGFBP-3 levels were comparable in all types of follicles and in serum. The 28 kDa IGFBP is glycosylated, and its level varied in parallel with the 24 kDa IGFBP, suggesting that these are variants of the recently identified IGFBP-4. IGFBP-1 was not detectable by immunoprecipitation and ligand blotting of FF obtained during the follicular phase. These data suggest that one or more IGFBPs present in higher levels in FF from atretic compared to healthy, developing follicles may play an important role in folliculogenesis and follicular atresia.