The effects of insulin-like growth factor-1 in prepubertal ovarian estradiol secretion

Abstract

Previously, it has been shown that insulin-like growth factor-1 (IGF-1) of peripheral origin acts centrally to stimulate the secretion of luteinizing hormone releasing hormone (LHRH) during the onset of puberty. This release of LHRH acts upon the pituitary gland to stimulate the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH), which increases estradiol (E₂) production by granulosa cells in the ovary. It has also been shown that IGF-1 has a facilitative effect on the ability of FSH to stimulate the production of E₂ by ovaries in the first proestrous phase of peripubertal development. However, whether or not this intraovarian effect of IGF-1 occurs prior to first proestrous and thus, has an earlier action to augment E₂ secretion during the late juvenile phase of the pubertal process in not known. This study was conducted to identify the role of serum IGF-1 at the ovarian level during the developmental stages that precede first ovulation and puberty. Results showed that, when administered to granulosa cells collected from rats in the late juvenile stage of puberty, IGF-1 did not show a facilitative effect on the ability of FSH to stimulate E₂ production. However, IGF-1 did facilitate FSH-induced E₂ production (p<0.01) in granulosa cells collected from rats in the first proestrous stage. These results suggest that IGF-1 plays an important role in the facilitation of E₂ production leading to first ovulation and puberty, but only after the ovary has developed into the proestrous phase of follicular development.