Mechanisms of action of growth hormone-releasing peptide-2 in bovine pituitary cells.
We conducted this study to investigate the mechanisms of action of growth hormone-releasing peptide-2 (D-Ala-D-beta Nal-Ala-Trp-D-Phe-Lys-NH2; GHRP-2) in bovine anterior pituitary primary cell culture. Doses of GHRP-2 from 10(-13) to 10(-7) M) increased (P < .05) GH secretion. The GHRP-2 (10(-7) M) and GH-releasing factor (GRF; 10(-7) M) administered together had an additive effect on the release of GH (P < .05). Somatostatin (1 microM) decreased GH secretion in response to GHRP-2 and(or) GRF (P < .05). Secretion of GH in response to GHRP-2 was blocked (P < .01) by a GRF receptor antagonist (.1 microM). Nifedipine (10 microM), a voltage-dependent Ca2+ channel blocker, inhibited (P < .01) GHRP-2-stimulated GH release. The GH release in response to GHRP-2 and 4 beta-phorbol-12-myristate-13-acetate (10(-7) M), a protein kinase C activator, was additive (P < .01). Forskolin (30 microM), a cAMP elevating agent, further stimulated (P < .01) the GH release in response to GHRP-2. Bovine GH concentrations in culture media were assayed by indirect competitive enzyme immunoassay. These results showed that GHRP-2 1) stimulates GH secretion from bovine pituitary cells, 2) may partially act via GRF receptor, 3) has GH secretion activity caused by Ca2+ influx via Ca2+ channels, and 4) may increase GH secretion via protein kinase C and cAMP pathways.
Roh
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Department of Animal Science, Obihiro University of Agriculture and Veterinary Medicine, Japan.
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M L
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Matsunaga
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Hidaka
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Hidari
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D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002417:Cattle / Q000378:metabolism*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D013006:Growth Hormone / Q000032:analysis / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology / Q000502:physiology; D006728:Hormones / Q000494:pharmacology*; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D013004:Somatostatin / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002121:Calcium Channel Blockers; D006728:Hormones; D009842:Oligopeptides; D005576:Colforsin; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; C091874:growth hormone-releasing peptide-2; D011493:Protein Kinase C; D009543:Nifedipine; D013755:Tetradecanoylphorbol Acetate