The effects of insulin, and insulin-like growth factors I and II on human ovarian follicles in long-term culture

The aim of this study was to investigate the effects of insulin and insulin-like growth factors I and II (IGF-I and IGF-II) on human ovarian follicles in vitro. Ovarian cortical tissue slices (0.1-0.3 cm) were cultured for 7 or 14 days on an artificial extracellular matrix and with FSH. The ovarian tissue cultures were stimulated by insulin (33 ng/ml), IGF-I (20 or 50 ng/ml) or IGF-II (20 ng/ml). Combined effects of IGF-I (20 ng/ml) or IGF-II (20 ng/ml) and insulin (33 ng/ml) were also studied. Proliferating cell nuclear antigen (PCNA) was selected for immunohistochemical examination activation of the mitotic cell cycle in granulosa cells. After 1 week of culture the number of follicles had decreased in all cases. After 2 weeks of culture the number of healthy follicles had decreased dramatically in control cultures. However, the loss of follicles could be prevented with insulin and IGFs. The number of atretic follicles was significantly lower in insulin cultures compared with control cultures after 2 weeks. The proportion of primary follicles was significantly increased in cultures treated with insulin, IGF-I (50 ng/ml) or IGF-II (20 ng/ml) compared with control cultures after 2 weeks. A similar effect was seen after co-treatment with IGF-II and insulin. There were significantly more PCNA-positive follicles in IGF-I cultures than in control cultures. These results suggest that insulin, IGF-I and IGF-II may act as survival factors for early stage human follicles. IGFs may also be involved in activation of the mitotic cell cycle of granulosa cells.