title: Stimulation of gonadotropin release and of ovarian development, by the administration of a gonadoliberin agonist and of dopamine antagonists, in female silver eel pretreated with estradiol.
abstract: In freshwater or seawater female silver eel, the release of gonadotropin (GTH) accumulated in the pituitary under estradiol (E2) influence could be stimulated by a conjugated treatment with a mammalian gonadoliberin agonist (GnRH-A = des-Gly10, (D-Ala6)-LH-RH ethylamide) and a blocker of dopamine receptor (pimozide). Furthermore, despite the GTH release, no reduction or even a significant increase in pituitary GTH levels were noted, indicating a stimulation of GTH synthesis. In consequence of the endogenous GTH release, a stimulation of ovarian development was induced, as demonstrated by the gonadosomatic index and histological study. Similar results were obtained with a combined treatment with GnRH-A and an inhibitor of catecholamine synthesis (L-alpha-methyl-3,4-dihydroxyphenylalanine). In contrast, no effect was produced by GnRH-A, pimozide, or L-alpha-methyl-DOPA, given alone. The results suggest that a double neuroendocrine mechanism (a lack of GnRH production and a dopaminergic inhibition of GnRH action) is involved in the prepubertal blockage of eel gonadotropic function before the reproductive migration.
authors.affiliation: Museum National d'Histoire Naturelle, UA 90 CNRS, Paris, France.
authors.forename: S
authors.initials: S
authors.lastname: Dufour
authors.forename: E
authors.initials: E
authors.lastname: Lopez
authors.forename: F
authors.initials: F
authors.lastname: Le Menn
authors.forename: N
authors.initials: N
authors.lastname: Le Belle
authors.forename: S
authors.initials: S
authors.lastname: Baloche
authors.forename: Y A
authors.initials: YA
authors.lastname: Fontaine
mesh_terms: D000811:Anguilla / Q000502:physiology*; D000818:Animals; D004298:Dopamine / Q000502:physiology*; D018492:Dopamine Antagonists; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D006062:Gonadotropins / Q000378:metabolism*; D008750:Methyldopa / Q000494:pharmacology; D010053:Ovary / Q000254:growth & development*; D010868:Pimozide / Q000494:pharmacology; D010902:Pituitary Gland / Q000378:metabolism
chemical_list: D018492:Dopamine Antagonists; D006062:Gonadotropins; D010868:Pimozide; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; C010661:surfagon; D008750:Methyldopa; D004298:Dopamine