INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) COLOCALIZES WITH IGF-BINDING PROTEINS (ICFBPS) IN MOUSE AND RAT OVARY

The cellular localization of insulin-like growth factor (ICF)-I mRNA, IGF-I peptide, and IGF-binding proteins (IGFBPs) was examined in mouse and rat ovaries through use of in situ hybridization and immunohistoc hemical methods. IGF-I mRNA was found to be most abundant in granulosa cells, although lower levels were also detected in cells of the theca interna, stroma, and corpus luteum. In contrast, IGF-I immunoreactivi ty was undetectable or low in granulosa cells, weak and variable in oo cytes, high in theca interna and the corpus luteum, and highest in the stroma. Antibodies directed against IGFBP-2, 3, and 5 yielded similar patterns of immunoreactivity to that observed for IGF-I peptide. The results indicate that IGF-I is synthesized in ovarian follicles, and t hat IGF-I of ovarian or systemic origin becomes localized to sites con taining IGFBPs in the ovary.