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The Presence and Ancestral Role of Gonadotropin-Releasing Hormone in the Reproduction of Scleractinian Coral, Euphyllia ancora

Institute of Marine Biology (W.-H.T., J.-S.H.) and Department of Aquaculture (W.-H.T., Y.-H.T., H.-F.W., C.-F.C.), National Taiwan Ocean University, Keelung 202, Taiwan; National Museum of Marine Biology and Aquarium (W.-H.T., Y.-H.L.), Pingtung 944, Taiwan; Department of Aquaculture, National Kaohsiung Marine University (S.-R.J., W.-S.Y.), Kaohsiung 811, Taiwan; and Unité Mixte de Recherche, 5178 Centre National de la Recherche Scientifique, Biologie des Organismes Marins et Ecosystèmes, Département des Milieux et Peuplements Aquatiques, Muséum National d’Histoire Naturelle (S.D.), 75231 Paris, France

Address all correspondence and requests for reprints to: Dr. Ching-Fong Chang, Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan. E-mail: B0044{at}mail.ntou.edu.tw.

The objectives of this study were to investigate the presence of immunoreactive GnRH (irGnRH) in scleractinian coral, Euphyllia ancora, study its seasonal variation, and evaluate its biological activity. irGnRH was detected and quantified in coral polyps. The biological activity of coral irGnRH was tested on pituitary cells from black porgy by evaluating its ability to stimulate LH release. Coral extracts (10^–9–10^–5 M irGnRH) as well as mammalian (m) GnRH agonist (10^–10–10^–6 M) had a similar dose-dependent effect on LH release. Furthermore, GnRH receptor antagonist dose-dependently inhibited the stimulation of LH release in response to coral extracts (10^–5 M irGnRH) and mGnRH agonist (10^–6 M). Peak levels of irGnRH (10-fold increase) were observed during the spawning period in a 3-yr investigation. Significantly higher aromatase activity and estradiol (E₂) levels were also detected during the period of spawning compared with the nonreproductive season. In in vivo experiments, mGnRH agonist time- and dose-dependently stimulated aromatase activity as well as the concentrations of testosterone and E₂ in free and glucuronided forms in coral. In conclusion, our data indicate that irGnRH does exist in coral, with its ability to stimulate LH release in fish. Seasonal variations of coral irGnRH, with a dramatic increase during the spawning period, concomitant to that in aromatase and E₂, as well as the ability of mGnRH agonist to stimulate coral aromatase, steroidogenesis, and steroid glucuronization suggest that irGnRH plays an important role in the control of oocyte growth and mass spawning in corals.