Insulin-like growth factor-I (IGF-I) stimulates the development of cultured rat pre-antral follicles

The aim of the present study is to investigate the effect of insulin-like g rowth factor (IGF-I) on the development of cultured rat pre-antral follicle s. Pre-antral follicles with a diameter between 140 and 160 mum are mechani cally isolated from ovaries of 10-day-old rats and cultured in groups for 6 days in FSH and insulin-containing serum-free medium in the absence or pre sence of IGF-I at concentrations of 1, 10, and 100 ng/ml, respectively. DNA content of the follicles before and after culture is measured to evaluate whether a possible growth is due to proliferation of follicular cells and t he ultrastructure of the cultured follicles is studied with transmission el ectron microscopy to evaluate the quality of follicles cultured under diffe rent conditions. Furthermore, reverse transcriptase polymerase chain reacti on (RT-PCR) is used to assess the gene expression of [GF-I and type I IGF r eceptor in pre-antral follicles. When follicles were cultured in medium con taining IGF-I at a concentration of 1 and 10 ng/ml, the increase in follicl e diameter after a 6-day culture differs significantly from that in the abs ence of IGF-I. The ultrastructure of follicles cultured in IGF-I-containing medium is better sustained when corn pared to that of follicles cultured i n the absence of IGF-I. Especially, theca cells, which are undergoing degen eration under controlled culture condition, demonstrate normal cellular ult rastructure with some characteristics of steroid-secreting cells in the pre sence of IGF-I, Moreover, in oocytes of follicles cultured in the presence of IGF-I, cortical granules are observed distributed along the ooplasma mem brane whereas cortical granules are hardly present in follicles cultured wi thout IGF-I. With RT-PCR, the presence of the mRNA of IGF-I and type I IGF receptor is demonstrated in both the somatic follicular cells and the oocyt es. Taken together, these results suggest that IGF-I, in the presence of fo llicle-stimulating hormone (FSH), enhances rat pre-antral follicle developm ent in vitro and supports the morphology of cultured pre-antral follicles. The stimulatory effect of exogenous IGF-I on the development of pre-antral follicle together with the gene expression ol: both IGF-I and type I IGF re ceptor in pre-antral follicles suggests the involvement of [GF-I in early f olliculogenesis and its actions are likely mediated by the putative type I IGF receptor, via both endocrine and paracrine/autocrine pathways. (C) 2001 Wiley-Liss, Inc.