title: Dopamine inhibition of gonadotropin and alpha-melanocyte-stimulating hormone release in vitro from the pituitary of the goldfish (Carassius auratus).
abstract: The purpose of the present investigation was to examine the receptor specificity of dopamine inhibition of gonadotropin (GtH) and alpha-melanocyte-stimulating hormone (alpha-MSH) release from the goldfish (Carassius auratus) pituitary in vitro. Pars distalis (PD) and neurointermediate lobe (NIL) fragments of the goldfish pituitary were superfused in vitro under various experimental paradigms; eluate from PD and NIL fragments was analyzed for (GtH) and (alpha-MSH), respectively. Spontaneous GtH release from PD fragments was relatively constant over 6 hr; continuous superfusion with dopamine reversibly inhibited spontaneous GtH release with an estimated ED50 of 10(-4.4) M. Domperidone, a specific D-2 receptor antagonist, reversed the inhibitory action of dopamine and increased spontaneous GtH release. Acute treatment of PD fragments with salmon GnRH (sGnRH) stimulated GtH release; dopamine inhibited GtH release from similarly treated fragments with an ED50 of 10(-7.5) M. The spontaneous release of alpha-MSH from NIL fragments was relatively constant over 6 hr; continuous superfusion with dopamine reversibly inhibited this release with an ED50 of 10(-7.2) M. Acute treatment of NIL fragments with thyrotropin-releasing hormone (TRH) caused acute dose-related increases in alpha-MSH release with an ED50 of 10(-8.2) M; dopamine reversibly inhibited alpha-MSH release from similarly treated fragments with an ED50 of 10(-7.7) M. Both stereoisomers of apomorphine, a dopamine agonist, inhibited GtH release from PD fragments treated with sGnRH; in contrast, alpha-MSH release from NIL fragments treated with TRH was stereospecifically inhibited by (-)-apomorphine, but not by (+)-apomorphine. Domperidone reversed (ED50 = 10(-6.6) M) dopamine (10(-6.3) M) inhibition of GtH release from PD fragments treated with sGnRH. In NIL fragments, the inhibitory action of dopamine (10(-6.3) M) was reversed by domperidone (ED50 = 10(-5.5) M), which restored the acute alpha-MSH release response to TRH. These results suggest the involvement of a low-affinity dopamine/neuroleptic receptor in dopamine inhibition of GtH and alpha-MSH release from the pituitary of the goldfish.
authors.affiliation: Department of Zoology, University of Alberta, Edmonton, Canada.
authors.forename: R J
authors.initials: RJ
authors.lastname: Omeljaniuk
authors.forename: M C
authors.initials: MC
authors.lastname: Tonon
authors.forename: R E
authors.initials: RE
authors.lastname: Peter
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D004294:Domperidone / Q000494:pharmacology*; D004298:Dopamine / Q000494:pharmacology*; D005260:Female; D006054:Goldfish; D006062:Gonadotropins / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011954:Receptors, Dopamine / Q000187:drug effects; D017448:Receptors, Dopamine D2
chemical_list: D006062:Gonadotropins; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D004294:Domperidone; D009074:Melanocyte-Stimulating Hormones; D001058:Apomorphine; D004298:Dopamine