Dopamine D2 receptors and secretion of FSH and LH: role of sexual steroids on the pituitary of the female rainbow trout

Author： Vacher C.   Ferrie`re F.   Marmignon M-H.   Pellegrini E.   Saligaut C.  

Publisher： Academic Press

ISSN： 0016-6480

Source： General and Comparative Endocrinology, Vol.127, Iss.2, 2002-06, pp. : 198-206

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Abstract

The role of sexual steroids in the modulation of a dopaminergic inhibitory tone on FSH and LH release was studied in the rainbow trout. The experiments were performed on previtellogenic trout, implanted or not with estradiol (E2), and vitellogenic trout. E2implant increased the circulating levels of LH and decreased the circulating levels of FSH in previtellogenic fish. The catecholamine inhibitorαMPT increased the circulating levels of LH, implanted or not withE2.αMPT increased circulating levels of LH in vitellogenic fish. This increase could be prevented by the dopaminergic agonist bromocryptine. The dopaminergic drugs had no effect on the circulating levels of FSH in all groups.E2 decreased mRNA levels of sGnRH1 and sGnRH2 in the telencephalon of previtellogenic fish. The dopaminergic treatments had no effect on mRNA levels of both forms of sGnRH in previtellogenic and vitellogenic fish. Primary cultures of pituitary cells were primed for three days with steroids (E2 or17α-hydroxy,20β-dihydroprogesterone (17α20βP)) before treatment with increasing doses of bromocryptine, associated or not with sGnRH.E2, but not17α20βP, potentiated the sGnRH-induced release of LH. Bromocryptine induced a slight dose-dependent decrease of sGnRH-induced release of LH. This decrease was potentiated by17α20βP.E2 and17α20βP had no effect on the release of FSH, but bromocryptine decreased the10-8 M sGnRH-induced release of FSH. In conclusion, the development of the dopaminergic inhibitory tone on gonadotropin release, at the onset of vitellogenesis, requires factors other than estradiol. E2should contribute in part to decrease the release of FSH. At the end of the reproductive cycle,17α20βP should reinforce the dopaminergic inhibitory tone.© 2002 Elsevier Science (USA)

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