Orexins suppress catecholamine synthesis and secretion in cultured PC12 cells.
New orexigenic peptides called orexin-A and -B have recently been described in neurons of the lateral hypothalamus and perifornical area. No orexins have been found in adipose tissues or visceral organs, including the adrenal gland. However, expression of the orexin-receptor 2 (OX2R) in the rat adrenal gland has been reported. To test the effects of orexins on peripheral organs, we investigated their effects on catecholamine synthesis and secretion in the rat pheochromocytoma cell line PC12. Orexin-A and -B (100 nM) significantly reduced basal and PACAP-induced tyrosine hydroxylase (TH) (the rate-limiting enzyme in the biosynthesis of catecholamines) mRNA levels. Orexin-A and -B (100 nM) also significantly inhibited the PACAP-induced increase in the cAMP level, suggesting that the suppressive effect on TH mRNA is mediated, at least in part, by the cAMP/protein kinase A pathway. Furthermore, orexin-A and -B (100 nM) significantly suppressed basal and PACAP-induced dopamine secretion from PC12 cells. Next, we examined whether orexin receptors (OX1R, OX2R) were present in the rat adrenal gland and PC12 cells. In the adrenal glands, OX2R was as strongly expressed as in the hypothalamus, but OX1R was not detected. On the other hand, neither OX1R nor OX2R was expressed in PC12 cells. However, binding assays showed equal binding of orexin-A and -B to PC12 cells, suggesting the existence in these cells of some receptors for orexins. These results indicate that orexins suppress catecholamine release and synthesis, and that the inhibitory effect is mediated by the cAMP/protein kinase A pathway.
Department of Clinical Pathology, University of Tsukuba, Tsukuba, Ibaraki, 305-8575, Japan.
T
T
Nanmoku
K
K
Isobe
T
T
Sakurai
A
A
Yamanaka
K
K
Takekoshi
Y
Y
Kawakami
K
K
Ishii
K
K
Goto
T
T
Nakai
D000310:Adrenal Gland Neoplasms / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D004298:Dopamine / Q000096:biosynthesis* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides / Q000378:metabolism* / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism / Q000494:pharmacology; D064446:Orexin Receptors; D000068797:Orexins; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000378:metabolism* / Q000473:pathology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide / Q000096:biosynthesis; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism
C495403:Adcyap1 protein, rat; D002352:Carrier Proteins; C578627:Hcrtr1 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D064446:Orexin Receptors; D000068797:Orexins; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D000242:Cyclic AMP; D014446:Tyrosine 3-Monooxygenase; D002118:Calcium; D004298:Dopamine