title: Somatostatin actions on a protein kinase C-dependent growth hormone secretagogue cascade.
abstract: In mammals, the ability of somatostatin (SS) to block growth hormone (GH) secretion is due, in part, to the inhibition of two key intracellular mediators, cAMP and Ca2+. We examined whether or not inhibition of Ca2+ signaling was mediating SS-induced inhibition basal, as well as gonadotropin-releasing hormone (GnRH; a protein kinase C (PKC)-dependent growth hormone secretagogue)-stimulated growth hormone (GH) release. Although SS reduced basal GH release from populations of pituitary cells, parallel reductions in [Ca2+]i were not observed within single, identified somatotropes. Similarly, application of GnRH and the PKC activator DiC8 elicited increases in [Ca2+]i and GH release, but abolition of the Ca2+ responses did not accompany SS inhibition of the GH responses. Surprisingly, while DiC8 potentiated SS inhibition of GH release, SS paradoxically increased DiC8-stimulated increases in [Ca2+]i. These data establish that abolition of Ca2+ signals is not a primary mechanism through which SS lowers basal, or inhibits GnRH-stimulated hormone release.
authors.affiliation: Department of Biological Sciences, CW 405 Biological Sciences Building, Faculty of Science, University of Alberta, Edmonton, T6G 2E9, Alberta, Canada.
authors.forename: W K
authors.initials: WK
authors.lastname: Yunker
authors.forename: J P
authors.initials: JP
authors.lastname: Chang
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D018929:Cell Culture Techniques; D004075:Diglycerides / Q000494:pharmacology; D006054:Goldfish; D007987:Gonadotropin-Releasing Hormone / Q000187:drug effects*; D013006:Growth Hormone / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008322:Mammals; D010902:Pituitary Gland / Q000166:cytology; D011493:Protein Kinase C / Q000494:pharmacology*; D013004:Somatostatin / Q000494:pharmacology*
chemical_list: D004075:Diglycerides; C044295:1,2-dioctanoylglycerol; D007987:Gonadotropin-Releasing Hormone; D013004:Somatostatin; D013006:Growth Hormone; D011493:Protein Kinase C; D002118:Calcium