Dopamine inhibition of gonadotropin and alpha-melanocyte-stimulating hormone release in vitro from the pituitary of the goldfish (Carassius auratus).
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.
Omeljaniuk
R J
RJ
Department of Zoology, University of Alberta, Edmonton, Canada.
Tonon
M C
MC
Peter
R E
RE
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
D006062:Gonadotropins; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D004294:Domperidone; D009074:Melanocyte-Stimulating Hormones; D001058:Apomorphine; D004298:Dopamine