title: Orexin-A augments voltage-gated Ca2+ currents and synergistically increases growth hormone (GH) secretion with GH-releasing hormone in primary cultured ovine somatotropes.
abstract: Orexins are recently discovered neuropeptides that play an important role in the regulation of hormone secretion, and their receptors have been recently demonstrated in the pituitary. The effects of orexin-A on voltage-gated Ca2+ currents and GH release in primary cultured ovine somatotropes were examined. The expression of orexin-1 receptor was demonstrated by RT-PCR in ovine somatotropes, from which Ca2+ currents were also isolated as L, T, and N currents. Application of orexin-A (100 nM) significantly and reversibly increased only the L current, and coadministration of orexin-A and GHRH (10 nM) showed an additive effect on this current, but no effect of orexin-A was observed on either T or N current. Furthermore, the orexin-A-induced increase in the L current was completely abolished by the inhibition of protein kinase C (PKC) activity using calphostin C (100 nM), phorbal 12,13-dibutyrate pretreatment (0.5 micro M) for 16 h or specific PKC inhibitory peptide PKC(19-36) (1 mM). However, the increase in L current by orexin-A was sustained when cells were preincubated with a specific protein kinase A blocker H89 (1 micro M) or a specific intracellular Ca2+ store depleting reagent thapsigargin (1 micro M). Finally, orexin-A alone did not significantly increase GH release, but coadministration of orexin-A and GHRH showed a synergistic effect on GH secretion in vitro. Our results therefore suggest that orexin-A may play an important role in regulating GHRH-stimulated GH secretion through the enhancement of the L-type Ca2+ current and the PKC-mediated signaling pathway in ovine somatotropes.
authors.affiliation: Prince Henry's Institute of Medical Research, Clayton, Victoria 3168, Australia.
authors.forename: Ruwei
authors.initials: R
authors.lastname: Xu
authors.forename: Qinling
authors.initials: Q
authors.lastname: Wang
authors.forename: Ming
authors.initials: M
authors.lastname: Yan
authors.forename: Maria
authors.initials: M
authors.lastname: Hernandez
authors.forename: Changhong
authors.initials: C
authors.lastname: Gong
authors.forename: Wah Chin
authors.initials: WC
authors.lastname: Boon
authors.forename: Yoko
authors.initials: Y
authors.lastname: Murata
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ueta
authors.forename: Chen
authors.initials: C
authors.lastname: Chen
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000494:pharmacology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004357:Drug Synergism; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D009479:Neuropeptides / Q000494:pharmacology*; D064446:Orexin Receptors; D000068797:Orexins; D010903:Pituitary Gland, Anterior / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D012313:RNA / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012756:Sheep; D015398:Signal Transduction
chemical_list: D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D012313:RNA; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium