Paracrine regulation of insulin-like growth factor I (IGF-I) and IGF-II on prostaglandins F2α and E2 synthesis by human corpus luteum in vitro:: A possible balance of luteotropic and luteolytic effects

The existence of a complete intraovarian insulin-like growth factor (IGF) system replete with ligands, receptors, and binding proteins has been demonstrated as well as the ability of IGF-I to positively affect steroidogenesis in human granulosa cells. Furthermore, we recently showed that IGF-I and IGF-II stimulate progesterone secretion by human luteal cells. As the PGs, PGE(2) and PGF(2 alpha), are classically known to have luteotropic and luteolytic effects, we wanted to determine whether the IGFs could affect the human luteal phase by influencing the PG system. For this reason, human luteal cells were cultured for different times (12, 24, and 48 h) with IGF-I, IGF-II (10-100ng/mL), and GH (100 ng/mL), and both PGs were assayed in the medium culture. We found that both IG F-I and IGF-II were able to stimulate PGE, synthesis in a time- and dose-dependent way, whereas they both inhibited PGF(2 alpha) production. GH, too, significantly :reduced PGF(2 alpha) synthesis; this effect was IGF-I mediated because it was reverted by increasing dilutions of an anti-IGF-I antibody. On the contrary, no GH effect was observed on PGE(2) production. In conclusion, based on these data and on our previous results, we speculate that IGFs could influence luteal steroidogenesis through PG system.