Neuropeptide Y inhibits spontaneous alpha-melanocyte-stimulating hormone (alpha-MSH) release via a Y(5) receptor and suppresses thyrotropin-releasing hormone-induced alpha-MSH secretion via a Y(1) receptor in frog melanotrope cells.
In amphibians, the secretion of alpha-MSH by melanotrope cells is stimulated by TRH and inhibited by NPY. We have previously shown that NPY abrogates the stimulatory effect of TRH on alpha-MSH secretion. The aim of the present study was to characterize the receptor subtypes mediating the action of NPY and to investigate the intracellular mechanisms involved in the inhibitory effect of NPY on basal and TRH-induced alpha-MSH secretion. Y(1) and Y(5) receptor mRNAs were detected by RT-PCR and visualized by in situ hybridization histochemistry in the intermediate lobe of the pituitary. Various NPY analogs inhibited in a dose-dependent manner the spontaneous secretion of alpha-MSH from perifused frog neurointermediate lobes with the following order of potency porcine peptide YY (pPYY) > frog NPY (fNPY) > porcine NPY (pNPY)-2-36) > pNPY-(13-36) > [D-Trp(32)]pNPY > [Leu(31),Pro(34)]pNPY. The stimulatory effect of TRH (10(-8)6 M) on alpha-MSH release was inhibited by fNPY, pPYY, and [Leu(31),Pro(34)]pNPY, but not by pNPY-(13-36) and [D-Trp(32)]pNPY. These data indicate that the inhibitory effect of fNPY on spontaneous alpha-MSH release is preferentially mediated through Y(5) receptors, whereas the suppression of TRH-induced alpha-MSH secretion by fNPY probably involves Y(1) receptors. Pretreatment of neurointermediate lobes with pertussis toxin (PTX; 1 microg/ml; 12 h) did not abolish the inhibitory effect of fNPY on cAMP formation and spontaneous alpha-MSH release, but restored the stimulatory effect of TRH on alpha-MSH secretion, indicating that the adenylyl cyclase pathway is not involved in the action of fNPY on TRH-evoked alpha-MSH secretion. In the majority of melanotrope cells, TRH induces a sustained and biphasic increase in cytosolic Ca(2+) concentration. Preincubation of cultured cells with fNPY (10(-7) M) or omega-conotoxin GVIA (10(-7) M) suppressed the plateau phase of the Ca(2+) response induced by TRH. However, although fNPY abrogated TRH-evoked alpha-MSH secretion, omega-conotoxin did not, showing dissociation between the cytosolic Ca(2+) concentration increase and the secretory response. Collectively, these data indicate that in frog melanotrope cells NPY inhibits spontaneous alpha-MSH release and cAMP formation through activation of a Y(5) receptor coupled to PTX- insensitive G protein, whereas NPY suppresses the stimulatory effect of TRH on alpha-MSH secretion through a Y(1) receptor coupled to a PTX-sensitive G protein-coupled receptor.
Galas
Ludovic
L
European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM, U-413, UA Centre National de la Recherche Scientifique, University of Rouen, 76821 Mont-Saint-Aignan, France.
Tonon
Marie-Christine
MC
Beaujean
Delphine
D
Fredriksson
Robert
R
Larhammar
Dan
D
Lihrmann
Isabelle
I
Jegou
Sylvie
S
Fournier
Alain
A
Chartrel
Nicolas
N
Vaudry
Hubert
H
D037361:Adenylate Cyclase Toxin; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017403:In Situ Hybridization; D007202:Indicators and Reagents; D009478:Neuropeptide Y / Q000031:analogs & derivatives / Q000494:pharmacology*; D037342:Pertussis Toxin; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011895:Rana ridibunda; D017476:Receptors, Neuropeptide Y / Q000187:drug effects / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013973:Thyrotropin-Releasing Hormone / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D000521:alpha-MSH / Q000378:metabolism*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D002121:Calcium Channel Blockers; D007202:Indicators and Reagents; D009478:Neuropeptide Y; D017476:Receptors, Neuropeptide Y; D010566:Virulence Factors, Bordetella; C097212:neuropeptide Y-Y1 receptor; C100568:neuropeptide Y5 receptor; D000521:alpha-MSH; D013973:Thyrotropin-Releasing Hormone; D020866:omega-Conotoxin GVIA; D000242:Cyclic AMP; D037342:Pertussis Toxin; D002118:Calcium