In vivo and in vitro effect of growth hormone on estradiol secretion by human granulosa cells

Abstract

GH therapy increases the ovarian response to gonadotropin stimulation in women presenting with ovaries that are relatively resistant to conventional gonadotropin therapy. As it is not completely certain whether GH modulates the actions of FSH on granulosa cells directly or via insulin-like growth factor-I (IGF-I) production, we studied its effect on steroid release by human granulosa cells obtained from subjects affected by unexplained or male factor infertility. In all subjects, superovulation for in vitro fertilization/embryo transfer was induced by treatment with gonadotropins or GH plus gonadotropins combined. The effects of the different in vivo treatments were evaluated in the conditioned medium obtained after the first 24 h of incubation; granulosa cells from patients treated with GH released higher amounts of estradiol and progesterone into the medium than did granulosa cells from patients treated with gonadotropins alone. When the release of steroid due to the in vivo treatment was exhausted, cells were subjected to increasing concentrations of GH in the presence or absence of 200 nmol anti-IGF Sm 1.2 monoclonal antibody (MoAb) or the antitype I receptor alpha IR3 MoAb. The results revealed that GH stimulates estradiol production in a dose-dependent fashion, and the presence of the MoAbs drastically reduces the GH effect. These data demonstrate that the established stimulatory effect of GH on ovarian function is dependent not only on the increased levels of circulating IGF-I, but also on a direct effect of GH on granulosa cells, which seems to be mediated at least in part by the autocrine action of IGF, particularly IGF-II. In fact, chromatographic analysis of medium conditioned by human granulosa cells revealed that these cells clearly produce IGF-II and IGF-binding proteins and only small amounts of IGF-I. Since GH appears to be able to increase the in vitro effect of both IGF-I and IGF-II, we can hypothesize a sensitization of the granulosa cells to the IGF-II produced by the cells themselves, which acts through the IGF-I receptor.