Luteinizing hormone and sexual steroid plasma levels after treatment of European sea bass with sustained-release delivery systems for gonadotropin-releasing hormone analogue

TitleLuteinizing hormone and sexual steroid plasma levels after treatment of European sea bass with sustained-release delivery systems for gonadotropin-releasing hormone analogue
Publication TypeJournal Article
Year of Publication2002
AuthorsMañanós, E, Carrillo M, Sorbera LA, Mylonas CC, Asturiano JF, Bayarri MJ, Zohar Y, Zanuy S
JournalJournal of Fish Biology
Volume60
Issue2
Pages328 - 339
KeywordsEuropean sea bass, Gonadotropin-releasing hormone analogue, Luteinizing hormone, Reproduction, Spawning induction, Spermiation
Abstract

Spermiating male European sea bass Dicentrarchus labrax were treated with gonadotropin-releasing hormone agonists (GnRHa), either a GnRHa injection (IN; 25 μg kg -1 body mass) or one of three types of controlled-release GnRHa-delivery systems: fast release implants (EVAc; 100 μg kg -1), slow release implants (EVSL; 100 μg kg -1) and slow release microspheres (MC; 50 μg kg -1). Luteinizing hormone (LH) release was highly stimulated by all GnRHa treatments, with elevated plasma levels lasting for 2 days in injected fish (IN) and 2, 4 and 6 weeks in controlled-release-treated fish (EVAc, MC and EVSL, respectively), correlating with a 1, 3, 5 and 5 week period of stimulation of milt production, respectively. Plasma levels of the androgens testosterone (T) and 11-ketotestosterone (11-KT), were not significantly affected by the GnRHa treatments. Plasma T was high at early spermiation and declined sharply near the end of this period. Plasma 11-KT levels declined continuously throughout the experiment. Levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P), a proposed maturation-inducing steroid (MIS) in European sea bass, fluctuated around 0.2-1 ng ml -1 and were not greatly affected by the treatments. These results indicated a close correlation between sustained stimulation of LH release, achieved by GnRHa-delivery systems, and long-term enhancement of milt production. They also show an absence of changes in the common sex steroids, associated with elevated LH and enhanced spermiation. © 2002 The Fisheries Society of the British Isles.

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