Effect of growth hormone (GH)-releasing peptide (GHRP) on the release of GH from cultured anterior pituitary cells in cattle.
The effect of His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (GHRP) on growth hormone (GH) release from cultured bovine anterior pituitary (AP) cells was studied in vitro with the interactive effects of GH-releasing factor (GRF: hpGRF (1-29)-NH2) and somatostatin (SRIF). The AP cells (5 x 10(4) cells per well) were incubated with media, and the media were changed 3 days after plating. After 3.5 days in culture, cells were incubated for 2 h with the peptides. GHRP stimulated GH release from cultured cells in a dose-related manner. At doses from 10(-11) to 10(-7) M GHRP, the amount of GH released was significantly greater than the controls (P < 0.05 to P < 0.001). The amounts of GH released at lower doses of GHRP (10(-14) to 10(-12) M) were not significantly different from the controls. GH concentrations after treatment with 10(-11) and 10(-7) M GHRP were 3.98 +/- 0.27 and 4.81 +/- 0.16 ng/ml, respectively. In experiments performed similarly, the 10(-7) M GHRH, GHRP, and combined treatment with GHRP plus GHRH increased GH 126, 57, and 139%, respectively (P < 0.001). The GH releasing effects of either GHRH alone or GHRP plus GHRH were significantly more potent than that of GHRP alone (P < 0.001). The additive effect was not significant when compared with GHRH alone. GH release induced by either GHRH or GHRP was significantly inhibited by SRIF (P < 0.01) compared with the untreated control. The inhibitory effect of SRIF in combined treatment with GHRP plus GHRH was significantly less than that of SRIF with GHRH or with GHRP (P < 0.01). The present study suggests that GH-releasing peptide (GHRP) induced GH release in cattle via a direct action on anterior pituitary cells in vitro.
Soliman
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Laboratory of Animal Reproduction, Faculty of Agriculture, Iwate University, Morioka, Japan.
Hashizume
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Kanematsu
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D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D013004:Somatostatin / Q000494:pharmacology
D009842:Oligopeptides; C041048:growth hormone releasing hexapeptide; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone