Effects of insulin-like growth factor-I on final oocyte maturation and steroid production in Fundulus heteroclitus |
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| Authors: | Z Negatu SM Hsiao RA Wallace |
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| Institution: | (1) Whitney Laboratory of University of Florida, St. Augustine, FL 32086, USA;(2) Department of Anatomy and Cell Biology, College of Medicine, University of Florida, Gainesville, FL 32610, USA;(3) Present address: Aqua Technologies Group, Inc., 5005 Sunshine State Parkway Feeder Rd., Fort Pierce, FL 34951, USA;(4) Division of Agricultural Sciences, Southern University and A&M College, Baton Rouge, LA 70813, USA |
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| Abstract: | Recent evidence has indicated the presence of IGF-I and IGF-I receptors in mammalian and teleost ovarian follicles. Since growth hormone (GH), which can be secreted from the pituitary concomitant with a gonadotropin as a response to gonadotropin-releasing hormone, generally acts to release IGF-I from tissues including the ovary, the effect of IGF-I itself on ovarian steroidogenesis and oocyte maturation was investigated in the model teleost, Fundulus heteroclitus. IGF-I was found to be without effect on ovarian follicle steroidogenesis, but initiated oocyte maturation in a dose-dependent manner even more rapidly and effectively than 17 ,20 -dihydroxy-4-pregnene-3-one (DHP), the naturally occurring maturation-inducing steroid. IGF-II also induced oocyte maturation in a dose-dependent manner. IGF-I induction of oocyte maturation occurred in the absence of DHP production by the granulosa cells (which is normally stimulated by gonadotropin), and could be inhibited by cycloheximide but not actinomycin D, thus implicating the role of protein synthesis. These results suggest that GH-stimulated release of ovarian IGF-I may have an even more direct role than DHP on the reinitiation of oocyte maturation. |
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| Keywords: | estradiol Fundulus heteroclitus growth hormone IGF-I IGF-II oocyte maturation ovarian follicle steroidogenesis signal transduction testosterone |
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