Growth hormone releasing hexapeptide (GHRP-6) activates the inositol (1,4,5)-trisphosphate/diacylglycerol pathway in rat anterior pituitary cells.
Growth hormone-releasing hexapeptide (GHRP-6) is known to stimulate secretion of growth hormone (GH) in vivo and in vitro in a variety of species. However, the cellular effects of GHRP-6 remain largely unknown. We have tested the influence of GHRP-6 on the inositol phospholipid second messenger system in cultured anterior pituitary cells. Cultured pituitary cells responded upon challenge with GHRP-6 with a dose-dependent release of GH. Moreover, incubation of GHRP-6 with pituitary cell cultures labelled with myo-[3H]inositol resulted in a dose-dependent rise in [3H]inositol phosphates. Brief stimulation of pituitary cells with GHRP-6 increased phosphorylation of MBP4-14, a specific protein kinase C substrate, when incubated with the cytosol- or plasma membrane fraction from the stimulated cells. Furthermore, introduction of MBP4-14 into the cytosol in digitonin permeabilized pituitary cells caused increased phosphorylation of this substrate. GHRP-6 induced a rise in intracellular Ca2+ in individual somatotrophs loaded with the Ca2+ indicator, Fura-2. Preincubation (3 min) with somatostatin (SRIF) diminished the Ca2+ spike elicited by GHRP-6, while no effect of SRIF was observed when added simultaneously with GHRP-6. These results indicate that GHRP-6-stimulated GH-secretion involves the diacylglycerol/inositol(1,4,5)trisphosphate pathway with a resulting rise in cytosolic Ca2+.
Division of Endocrinology and Metabolism, Department of Physiology, The Panum Insititue, University of Copenhagen, Denmark.
S E
SE
Mau
M R
MR
Witt
O J
OJ
Bjerrum
T
T
Saermark
H
H
Vilhardt
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D013006:Growth Hormone / Q000378:metabolism; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D004676:Myelin Basic Protein / Q000737:chemistry / Q000378:metabolism; D009842:Oligopeptides / Q000737:chemistry / Q000494:pharmacology*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015290:Second Messenger Systems / Q000187:drug effects; D013004:Somatostatin / Q000494:pharmacology
D004075:Diglycerides; D004676:Myelin Basic Protein; D009842:Oligopeptides; D010446:Peptide Fragments; C066466:myelin basic protein 1-14; C041048:growth hormone releasing hexapeptide; D013004:Somatostatin; D015544:Inositol 1,4,5-Trisphosphate; D013006:Growth Hormone; D011493:Protein Kinase C; D002118:Calcium