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Original Articles |
Imperial College School of Medicine at St. Marys, Norfolk Place, London, W2 1PG, United Kingdom
Address all correspondence and requests for reprints to: Debbie S. Willis, Department of Obstetrics and Gynaecology, Imperial College School of Medicine at St. Marys, Norfolk Place, London, W2 1PG, United Kingdom.
Abstract
In experimental animal models, insulin-like growth factors (IGFs) have been found to be more potent stimulators of ovarian function than insulin. In human theca cells, however, insulin, IGF-I, and IGF-II have similar effects on androgen production. The relative effects of insulin and IGFs on human granulosa cell steroidogenesis is unknown. Furthermore, it is unclear whether effects of IGF-II on steroidogenesis are mediated by the type-I or type-II IGF receptor.
The effects of insulin, IGF-I, and IGF-II on human granulosa cell
steroidogenesis were compared in vitro. As expected,
insulin, IGF-I, and IGF-II enhanced steroidogenesis. Previously, IGF-II
has been shown to enhance granulosa cell steroid production after
insulin preincubation. In this study, an effect of IGF-II, independent
of insulin priming, also was observed. In granulosa cell cultures from
small antral follicles (
13 mm), insulin and IGF-I stimulated steroid
production to a similar degree, whereas IGF-II was less effective. In
contrast, IGFs were more effective than insulin (IGF-I >
IGF-II > insulin) in granulosa cells isolated from preovulatory
follicles. IGF-I and IGF-II actions were mediated via the type-1 IGF
receptor.
The increased responsiveness of mature granulosa cells to IGFs may be an important mechanism by which granulosa cells increase their steroidogenic output in the preovulatory follicle.
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