Effect of phorbol esters on the release of growth hormone and prolactin from rat pituitary cells cultured in monolayer

1984 ◽  
Vol 107 (2) ◽  
pp. 185-191 ◽  
Author(s):  
Eiji Ohmura ◽  
Toshio Tsushima ◽  
Hitomi Murakami ◽  
Kae Wakai ◽  
Kazuo Shizume
Keyword(s):  
Growth Hormone ◽  
Protein Kinase ◽  
Phorbol Ester ◽  
Time Course ◽  
Phorbol Esters ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Rat Pituitary ◽  
Rat Pituitary Cells ◽  
Cells Cultured

Abstract. The effect of phorbol diester tumour promoters on the release of growth hormone (GH) and prolactin (Prl) was studied in rat pituitary cells cultured in monolayer. 12-O-tetradecanoyl phorbol-13-acetate (TPA), the most potent phorbol ester, stimulated GH accumulation in the cultured medium in a dose-dependent manner. TPA also stimulated Prl accumulation. A time course study indicated that TPA mainly stimulates release of GH. The maximal stimulation of GH release by TPA (100 ng/ml) was 3–4-fold over control. Phorbol-12,13-dibutyrate (PDB), another tumour-promoting phorbol ester, stimulated GH release to an extent similar to that of TPA, while a biologically inactive compound, phorbol-12,13-diacetate (PDA), had no effect. TPA-stimulated GH release was not affected by the presence of indomethacin, an inhibitor of prostaglandin (PG) synthesis, indicating that PG is not involved in the process of TPA-stimulated GH release. Co++, a competitive antagonist of Ca++, at 2.0 mm completely suppressed the GH release induced by TPA, and this inhibition was partially reversed by the addition of 2.0 mm Ca++. Verapamil, a Ca++ channel blocker, reduced TPA-stimulated GH release, and trifluoperazine, an inhibitor of Ca-calmodulin formation, had a similar effect. Somatostatin (SRIF) also inhibited the GH release by TPA. These observations are compatible with the idea that Ca++ may be involved in the process of TPA-stimulated GH release. Since TPA has been reported to activate a Ca++- and phospholipiddependent protein kinase (protein kinase C), it is possible that TPA stimulate GH release by activating the enzyme. Further studies are required to clarify this point.

Involvement of thioredoxin in the regulation of growth hormone secretion in rat pituitary cell cultures

2001 ◽  
Vol 281 (2) ◽  
pp. E269-E274 ◽  
Author(s):  
Ikue Hata ◽  
Yosuke Shigematsu ◽  
Yusei Ohshima ◽  
Hirokazu Tsukahara ◽  
Kazuo Fujisawa ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Gh Secretion ◽  
Anterior Pituitary Cells ◽  
Rat Pituitary ◽  
Rat Pituitary Cells

We report here an examination of the effect of thioredoxin (TRX) on the secretion of growth hormone (GH) from rat anterior pituitary cells in vitro. Treatment of rat pituitary cells with growth hormone-releasing factor (GRF), but not GH, led to a significant increase in intracellular TRX protein levels. GRF, recombinant human TRX (rhTRX), and a combination thereof were all shown to induce immediate GH secretion from pituitary cells, as evidenced by perifusion experiments. RhTRX, but not other reducing agents such as β-mercaptoethanol and N-acetyl-l-cysteine, augmented GRF-stimulated and -unstimulated GH secretion from rat pituitary cells in a dose-dependent manner. RhTRX did not significantly affect the GH mRNA expression of pituitary cells stimulated in the presence or absence of GRF. In addition, rhTRX-augmented GH secretion was not significantly affected by the presence of cycloheximide. Collectively, these findings suggest that TRX is induced by stimulation with GRF and plays a regulatory role in GH secretion from rat anterior pituitary cells by enhancing the secretion of stored GH, rather than by the synthesis of GH.

Phorbol ester pretreatment attenuates the growth hormone (GH) response to GH-releasing factor in cultured rat pituitary cells

1988 ◽  
Vol 118 (3) ◽  
pp. 423-428 ◽  
Author(s):  
E. Ohmura ◽  
M. Okada ◽  
Y. Ohba ◽  
N. Onoda ◽  
T. Sano ◽  
...  
Keyword(s):  
Phorbol Ester ◽  
Suppressive Effect ◽  
Inhibitory Effect ◽  
Complete Suppression ◽  
Pituitary Cells ◽  
Rat Pituitary ◽  
Prolonged Culture ◽  
Subsequent Exposure ◽  
Rat Pituitary Cells ◽  
Cells Cultured

ABSTRACT The effect of phorbol ester pretreatment on rat (r) GH release induced by GH-releasing factor (GRF) or 8-bromo-cyclic (c)AMP was investigated using rat pituitary cells cultured in monolayers. Pretreatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 3 h significantly suppressed the rGH release induced by GRF, but not that by 8-bromo-cAMP 20 h later; this suppressive effect of TPA was concentration-dependent from 8 to 160 nmol/l, and complete suppression was observed after pretreatment with 80–160 nmol TPA/l. Production of cAMP by pituitary cells stimulated with GRF was similarly attenuated in TPA-pretreated cells. The rGH responsiveness to GRF of these cells was fully recovered on prolonged culture (40 h), suggesting that the inhibitory effect of TPA is reversible. In contrast, pretreatment with GRF (5 nmol/l) resulted in suppression of the rGH response to subsequent exposure to GRF (5 nmol/l) or 8-bromo-cAMP (10 mmol/l), but not to TPA. These observations suggest that pretreatment with TPA modifies the rGH response to GRF at steps before the formation of cAMP. J. Endocr. (1988) 118, 423–428

Tamoxifen inhibits phorbol ester stimulated osteoclastic bone resorption: An effect mediated by calmodulin

2000 ◽  
Vol 78 (6) ◽  
pp. 715-723 ◽  
Author(s):  
John P Williams ◽  
Margaret A McKenna ◽  
Allyn M Thames III ◽  
Jay M McDonald
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Bone Resorption ◽  
Phorbol Ester ◽  
Phorbol Esters ◽  
Fold Increase ◽  
Dependent Manner ◽  
Osteoclast Activity ◽  
Kinase C ◽  
Protein Kinase Cα

Tamoxifen inhibits bone resorption by disrupting calmodulin-dependent processes. Since tamoxifen inhibits protein kinase C in other cells, we compared the effects of tamoxifen and the phorbol ester, phorbol myristate acetate, on osteoclast activity. Phorbol esters stimulate bone resorption and calmodulin levels four-fold (k0.5 = 0.1–0.3 µM). In contrast, tamoxifen inhibited osteoclast activity ~60% with an IC50 of 1.5 µM, had no apparent effect on protein kinase C activity in whole-cell lysates, and reduced protein kinase Cα recovered by immunoprecipitation 75%. Phorbol esters stimulated resorption in a time-dependent manner that was closely correlated with a similar-fold increase in calmodulin. Protein kinase Cα, β, δ, ε, and ζ were all down-regulated in response to phorbol ester treatment. Tamoxifen and trifluoperazine inhibited PMA-dependent increases in bone resorption and calmodulin by 85 ± 10%. Down-regulation of protein kinase C isoforms by phorbol esters suggests that the observed increases in bone resorption and calmodulin levels are most likely due to a mechanism independent of protein kinase C and dependent on calmodulin. In conclusion, the data suggest that protein kinase C negatively regulates calmodulin expression and support the hypothesis that the effects of both phorbol esters and tamoxifen on osteoclast activity is mediated by calmodulin.Key words: osteoclast, calmodulin, tamoxifen, osteoporosis, protein kinase C.

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