Direct effects of prolactin and dopamine on the gonadotroph response to GnRH.
The intrapituitary mechanisms underlying the inhibitory actions of hyperprolactinaemia on the reproductive axis remain unclear. Previous work on primary pituitary cultures revealed combined suppressive effects of prolactin (PRL) and dopamine on the gonadotrophin response to GnRH. However, whether these effects occur directly at the level of the gonadotroph and are accompanied by changes in gene expression is still unresolved. Here, alphaT(3)-1 and LbetaT2 cells were used to investigate the effects of PRL and dopamine on gonadotrophin synthesis and release in gonadotroph monocultures under basal and GnRH-stimulated conditions. PRL receptor and dopamine receptor mRNA expressions were first determined by RT-PCR in both cell lines. Then, PRL and the dopamine agonist bromocriptine (Br), alone or in combination, were shown to block the maximal alpha-subunit and LHbeta-subunit mRNA responses to a dose-range of GnRH. The LH secretory response was differentially affected by treatments. GnRH dose-dependently stimulated LH release, with a 4-5 fold increase at 10(-8) M GnRH. Unexpectedly, PRL or Br stimulated basal LH release, with PRL, but not Br, enhancing the LH secretory response to GnRH. This effect was, however, completely blocked by Br. These results reveal direct effects of PRL and dopamine at the level of the gonadotroph cell, and interactions between these two hormones in the regulation of gonadotrophin secretion. Moreover, uncoupling between LH synthesis and release in both the basal and the GnRH-stimulated responses to PRL and dopamine was clearly apparent.
Henderson
Helen L
HL
Department of Anatomy, University of Bristol, Bristol BS2 8EJ, England, UK.
Townsend
Julie
J
Tortonese
Domingo J
DJ
D000818:Animals; D002478:Cells, Cultured; D004298:Dopamine / Q000494:pharmacology*; D052681:Gonadotrophs / Q000187:drug effects* / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics; D020935:MAP Kinase Signaling System; D051379:Mice; D011388:Prolactin / Q000494:pharmacology*; D017448:Receptors, Dopamine D2 / Q000032:analysis / Q000502:physiology; D011981:Receptors, Prolactin / Q000032:analysis / Q000502:physiology
D037101:Luteinizing Hormone, beta Subunit; D017448:Receptors, Dopamine D2; D011981:Receptors, Prolactin; D007987:Gonadotropin-Releasing Hormone; D011388:Prolactin; D007986:Luteinizing Hormone; D004298:Dopamine