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Title: EXPRESSION OF INSULIN-LIKE GROWTH FACTORS AND THEIR BINDING PROTEINS BY PORCINE OVARIAN CELLS

Author
item HAMMOND, J - MS HERSHEY MED CTR, PA
item GRIMES, R - MS HERSHEY MED CTR, PA
item SAMARAS, S - MS HERSHEY MED CTR, PA
item HELMS, K - MS HERSHEY MED CTR, PA
item Guthrie, Howard

Submitted to: Serono Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The incidence of long infertile periods and low ovulation rate in female swine is a serious economic problem that can occur after weaning or during environmental stress. Pigs that fail to be in estrus or fail to conceive increase producer costs by 25%. We hypothesized that intra ovarian insulin- like growth factors (IGFs), and IGF binding proteins (IGFBPs) amplify and attenuate, respectively, the actions of gonadotropins on follicular growth and steroidogenesis. The epidermal growth factor-like peptides are found in luteal tissue and luteinized granulosa cells. IGF-I protein and messenger ribonucleic acid (mRNA) content were positively associated with follicle maturation. In contrast, expression of IGFBP-2, -4, and -5 decreased during follicle maturation and was high in small healthy or atretic follicles. We conclude that actions of the IGF/IGFBP system could be involved in determination of whether follicles ovulate or die. We will use these results as a basis for studies on the molecular regulation of the IGF/IGFB system and its role in follicular growth and maturation. These studies will provide knowledge required better regulate ovulation rate.

Technical Abstract: Growth of ovulatory follicles cannot be wholly explained by changes in the secretion of gonadotropins. Little is known about how intra ovarian factors regulate ovarian follicle maturation. The purpose this review is to describe our investigations into the action and regulation of intra ovarian insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs). Increased expression of IGF-I protein and mRNA during preovulatory maturation indicates that it plays a role in cytodifferentiation and proliferation of follicle cells. IGFBP-2 and lower molecular weight forms which likely represent IGFBP-4, glycosylated IGFBP-4, and IGFBP-5 are highest in immature, healthy and perhaps in atretic follicles. Expression IGFBP-2, -4 and -5 decrease during the greater part of preovulatory maturation, then IGFBP-4 and -5, but not -2 increase in luteinizing follicular tissue following the preovulatory LH surge. IGFBP-3 mRNA is predominantly expressed in luteal tissue and minimally expressed in follicular tissue in spite of high accumulation IGFBP-3 protein in follicular fluid and granulosa cell conditioned medium. Principle regulatory factors are gonadotropins and cAMP which inhibit IGFBP production, and growth factors (IGFs, insulin, and EGF) which enhance production in vitro. Results indicate that IGFBPs function to inhibit or attenuate growth and steroidogenesis in non-ovulatory follicles. Actions of the IGF/IGFBP system could be involved in determination of whether follicles undergo preovulatory maturation or die.