Effects of activators of different intracellular signaling pathways on steroid production by goldfish vitellogenic ovarian follicles.
For the present study, calcium ionophore A23187 and phorbol 12-myristate 13-acetate (PMA) were used to investigate the possible roles that changes in intracellular calcium content and protein kinase C activation play in steroid production by goldfish vitellogenic ovarian follicles (0.2-0.7 mm in diameter) incubated in vitro. While largely ineffective when tested alone, PMA and A23187 exhibit synergism leading to increased testosterone and 17 beta-estradiol production. Production of both steroids was also increased by the addition of either human chorionic gonadotropin (hCG) or forskolin, a direct activator of adenylate cyclase. However, hCG- and forskolin-stimulated testosterone and 17 beta-estradiol production was attenuated by PMA and A23187 either alone or in combination. Both drugs blocked the stimulatory actions of hCG on adenosine 3',5'-cyclic monophosphate (cAMP) formation. PMA also influenced steroid production at sites distal to cAMP formation as it blocked the actions of dibutyryl cAMP a permeant analog of cAMP. This action was prior to cholesterol side-chain cleavage as PMA had no effect on the metabolism of 25-hydroxycholesterol to testosterone or 17 beta-estradiol. By comparison, A23187 had no effects on either dbcAMP- or 25-hydroxycholesterol-stimulated steroid production. Separation of vitellogenic and prematurational, full-grown (0.9-1.1 mm in diameter) ovarian follicles from the same fish lead to the demonstration of opposing actions of A23187 in the two follicle types. Whereas A23187 inhibited hCG-stimulated steroid production in vitellogenic follicles, it had an additive effect on the stimulatory action of hCG on testosterone production by prematurational, full-grown ovarian follicles. In conclusion, these studies on vitellogenic ovarian follicles demonstrate specific regulatory actions of calcium and protein kinase C at multiple steps in the steroidogenic cascade and that ovarian responsiveness to calcium changes during the course of follicle development in the goldfish.
Srivastava
R K
RK
Department of Zoology, University of Guelph, Ontario, Canada.
Van der Kraak
G
G
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D004958:Estradiol / Q000096:biosynthesis; D005260:Female; D006054:Goldfish / Q000378:metabolism*; D006080:Ovarian Follicle / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013256:Steroids / Q000096:biosynthesis*; D013739:Testosterone / Q000096:biosynthesis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014818:Vitellogenesis
D006063:Chorionic Gonadotropin; D013256:Steroids; D000001:Calcimycin; D013739:Testosterone; D004958:Estradiol; D000242:Cyclic AMP; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium