IN-VIVO HORMONAL-REGULATION OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-5 MESSENGER-RNA IN THE IMMATURE RAT OVARY

OBJECTIVE: Despite the potential importance of insulin-like growth fac tor binding protein-5 (IGFBP-5) to follicular development, the hormona l regulation of this antigonadotropic IGFBP has not been investigated. Therefore, it was the objective of this study to eludicate the role o f gonadotropins and estrogen in the in vivo regulation of IGFBP-5 mRNA expression. METHODS: Two models of follicular development in immature vats were used. Specifically, vats were hypophysectomized and treated with FSH and/or diethylstilbestrol (DES). Alternatively, terminal fol licular development was induced in intact immature vats by pregnant ma re serum gonadotropin (PMSG) and hCG. The IGFBP-5 mRNA in whole ovaria n RNA was assayed by Northern blot hybridization. Localization of expr ession in PMSG and hCG-stimulated ovaries was further assessed by in s itu hybridization. RESULTS: Expression of lGFBP-5 mRNA was increased i n ovaries from hypophysectomized vats. Treatment with FSH and/or DES d id not alter the abundance of this mRNA. Treatment with PMSG induced a transient increase in IGFBP-5 expression that was localized in a subs et of alpha-inhibin-negative follicles. At later times after PMSG, IGF BP-5 expression persisted in the surface epithelium but was not detect ed in large preovulatory follicles. In vitro studies affirmed the anti gonadotropic action of IGFBP-5. CONCLUSION: In vivo expression of IGFB P-5 in the vat ovary is moderated by hormonal treatment both in terms of total expression and follicular localization.