Melanin-concentrating hormone reduces somatolactin release from cultured goldfish pituitary cells.
Melanin-concentrating hormone (MCH)-containing neurons directly innervate the adenohypophysis in the teleost pituitary. We examined immunohistochemically the relationship between MCH-containing nerve fibres or endings and somatolactin (SL)-producing cells in the goldfish pituitary. Nerve fibres or endings with MCH-like immunoreactivity were identified in the neurohypophysis in close proximity to the adenohypophysial cells showing SL-like immunoreactivity. We also examined the effect of MCH on SL release from cultured goldfish pituitary cells and SL synthesis using a cell immunoblot and a real-time PCR method. Treatment of individually dispersed pituitary cells with MCH 10(-7) M for 3 h decreased the area of SL-like immunoreactivity on immunoblots, and MCH-induced reductions in SL release were blocked by treatment with the mammalian MCH receptor (MCHR) antagonist, compound-30, at a concentration of 10(-5) M. Treatment with 10(-7) M MCH for 3 h did not affect sl-alpha and -beta (smtla and -b as given in the Zfin Database) mRNA expression levels. These led us to explore the signal transduction mechanism leading to the inhibition of SL release, for which we examined whether MCH-induced reductions in SL release are mediated by the G(i) or G(q) protein-coupled signalling pathway. The MCH-induced reductions in SL release were abolished by treatment with the G(i/o) protein inhibitors, NF023 (10(-5) M) or pertussis toxin (260 ng/ml), but not by the phospholipase C inhibitor, U-73122 (3x10(-6) M). These results indicate that MCH can potentially function as a hypothalamic factor suppressing SL release via the MCHR, and subsequently through the G(i) protein to inhibit the adenylate cyclase/cAMP/protein kinase A-signalling pathway in goldfish pituitary cells.
Tanaka
Mio
M
Laboratory of Regulatory Biology, Graduate School of Science and Engineering, University of Toyama, 3190-Gofuku, Toyama 930-8555, Japan.
Azuma
Morio
M
Nejigaki
Yumika
Y
Saito
Yumiko
Y
Mizusawa
Kanta
K
Uchiyama
Minoru
M
Takahashi
Akiyoshi
A
Shioda
Seiji
S
Matsuda
Kouhei
K
D000818:Animals; D002478:Cells, Cultured; D004963:Estrenes; D005260:Female; D029941:Fish Proteins / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism*; D006054:Goldfish / Q000378:metabolism*; D007028:Hypothalamic Hormones / Q000378:metabolism*; D015151:Immunoblotting; D008297:Male; D008543:Melanins / Q000378:metabolism*; D009412:Nerve Fibers / Q000502:physiology*; D037342:Pertussis Toxin; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D010907:Pituitary Hormones / Q000378:metabolism*; D011760:Pyrrolidinones; D012333:RNA, Messenger / Q000378:metabolism; D011979:Receptors, Pituitary Hormone / Q000037:antagonists & inhibitors; D013498:Suramin / Q000031:analogs & derivatives; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D004963:Estrenes; D029941:Fish Proteins; D006023:Glycoproteins; D007028:Hypothalamic Hormones; D008543:Melanins; C105374:NF023; D010907:Pituitary Hormones; D011760:Pyrrolidinones; D012333:RNA, Messenger; D011979:Receptors, Pituitary Hormone; C092274:melanin-concentrating hormone receptor; C064448:somatolactin protein, fish; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D013498:Suramin; C019463:melanin-concentrating hormone; D037342:Pertussis Toxin; D010738:Type C Phospholipases