title: Stimulatory effect of ghrelin on isolated porcine somatotropes.
abstract: Research on the mechanism for growth hormone secretagogue (GHS) induction of growth hormone secretion led to the discovery of the GHS receptor (GHS-R) and later to ghrelin, an endogenous ligand for GHS-R. The ability of ghrelin to induce an increase in the intracellular Ca(2+) concentration - [Ca(2+)](i) - in somatotropes was examined in dispersed porcine pituitary cells using a calcium imaging system. Somatotropes were functionally identified by application of human growth hormone releasing hormone. Ghrelin increased the [Ca(2+)](i) in a dose-dependent manner in 98% of the cells that responded to human growth hormone releasing hormone. In the presence of (D-Lys(3))-GHRP-6, a specific receptor antagonist of GHS-R, the increase in [Ca(2+)](i) evoked by ghrelin was decreased. Pretreatment of cultures with somatostatin or neuropeptide Y reduced the ghrelin-induced increase of [Ca(2+)](i). The stimulatory effect of ghrelin on somatotropes was greatly attenuated in low-calcium saline and blocked by nifedipine, an L-type calcium channel blocker, suggesting involvement of calcium channels. In a zero Na(+) solution, the stimulatory effect of ghrelin on somatotropes was decreased, suggesting that besides calcium channels, sodium channels are also involved in ghrelin-induced calcium transients. Either SQ-22536, an adenylyl cyclase inhibitor, or U73122, a phospholipase C inhibitor, decreased the stimulatory effects of ghrelin on [Ca(2+)](i) transiently, indicating the involvement of adenylyl cyclase-cyclic adenosine monophosphate and phospholipase C inositol 1,4,5-trisphosphate pathways. The nonpeptidyl GHS, L-692,585 (L-585), induced changes in [Ca(2+)](i) similar to those observed with ghrelin. Application of L-585 after ghrelin did not have additive effects on [Ca(2+)](i). Preapplication of L-585 blocked the stimulatory effect of ghrelin on somatotropes. Simultaneous application of ghrelin and L-585 did not cause an additive increase in [Ca(2+)](i). Our results suggest that the actions of ghrelin and synthetic GHS closely parallel each other, in a manner that is consistent with an increase of hormone secretion.
authors.affiliation: Neuroscience Program, Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Glavaski-Joksimovic
authors.forename: Ksenija
authors.initials: K
authors.lastname: Jeftinija
authors.forename: Colin G
authors.initials: CG
authors.lastname: Scanes
authors.forename: Lloyd L
authors.initials: LL
authors.lastname: Anderson
authors.forename: Srdija
authors.initials: S
authors.lastname: Jeftinija
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D000831:Animals, Newborn; D001552:Benzazepines / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D018929:Cell Culture Techniques; D004305:Dose-Response Relationship, Drug; D054439:Ghrelin; D013006:Growth Hormone / Q000187:drug effects / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000378:metabolism*; D007150:Immunohistochemistry; D009478:Neuropeptide Y / Q000378:metabolism / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D036361:Peptide Hormones / Q000008:administration & dosage / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D015398:Signal Transduction / Q000187:drug effects*; D015222:Sodium Channels / Q000378:metabolism; D013004:Somatostatin / Q000378:metabolism / Q000494:pharmacology; D013552:Swine; D013777:Tetrazoles / Q000378:metabolism / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D001552:Benzazepines; D020746:Calcium Channels, L-Type; D054439:Ghrelin; C091588:L 692585; D009478:Neuropeptide Y; D036361:Peptide Hormones; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D015222:Sodium Channels; D013777:Tetrazoles; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D010738:Type C Phospholipases; D009543:Nifedipine; D002118:Calcium