Insulin-like growth factor family in Graafian follicle development and function.
The insulin-like growth factor (IGF) family plays an important role in follicle development, dominant follicle growth and steroidogenesis, and follicular atresia. Insulin-like growth factor (IGF)-II is the primary IGF in human ovary, acting as a mediator of gonadotropin action. IGF-II stimulates granulosa steroidogenesis, and its actions, along with those of follicle-stimulating hormone (FSH), are inhibited by IGF binding protein (IGFBP)-4. At the time of follicle selection, in the estrogen-dominant follicle, granulosa IGF-II synthesis increases dramatically. Simultaneously, in the selected follicle, IGFBP-4, an inhibitor of IGF-II action and abundant within androgen-dominant follicles, is proteolyzed by a specific IGFBP-4 protease, resulting in decreased affinity of IGFBP-4 for IGF-II. The IGFBP-4 protease has recently been identified in human ovary as pregnancy-associated plasma protein-A (PAPP-A). In the Graafian follicle, IGF-II bioavailability is increased to act as a mediator of FSH action, by increased synthesis of this peptide and concomitant decrease in an inhibitor of its actions by proteolysis of IGFBP-4.
Giudice
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LC
Division of Reproductive Endocrinology and Infertility, Center for Research on Women's Health and Reproductive Medicine, Department of Gynecology and Obstetrics, Stanford University Medical Center, Stanford, California 94305-5317, USA. giudice@stanford.edu
D000818:Animals; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry; D015870:Gene Expression; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D007335:Insulin-Like Growth Factor II / Q000502:physiology; D006080:Ovarian Follicle / Q000254:growth & development / Q000502:physiology*; D010053:Ovary / Q000502:physiology; D017451:Receptors, Somatomedin / Q000235:genetics; D013002:Somatomedins / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D018974:Insulin-Like Growth Factor Binding Protein 4; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II