In VitroApplication of Testosterone Potentiates Gonadotropin-Releasing Hormone-Stimulated Gonadotropin-II Secretion from Cultured Goldfish Pituitary Cells

Lo, Angelina; Chang, John P.

doi:10.1006/gcen.1998.7117

Cited by 18 publications

(16 citation statements)

References 43 publications

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“…Caffeine and sGnRH have similar seasonal profiles with respect to their maximum efficacy in releasing GTH-II in vitro, with both being most efficient in between the stages of gonadal recrudescence and maturation (20,31). Compared with the kinetics of cGnRH-II-stimulated GTH-II release, responses to sGnRH become very extended during this period (31), raising the possibility that the prolonged component may be due to the recruitment of caffeine-sensitive intracellular Ca 2ϩ stores. Ca 2ϩ signals generated by sGnRH also have slower rates of rise and more often exhibit a prolonged monophasic waveform compared with those of cGnRH-II (24).…”

Section: Discussionmentioning

confidence: 95%

“…It is tempting to speculate that caffeine-sensitive Ca 2ϩ stores may be involved in the differential control of gonadotrope function by sGnRH and cGnRH-II (27). Caffeine and sGnRH have similar seasonal profiles with respect to their maximum efficacy in releasing GTH-II in vitro, with both being most efficient in between the stages of gonadal recrudescence and maturation (20,31). Compared with the kinetics of cGnRH-II-stimulated GTH-II release, responses to sGnRH become very extended during this period (31), raising the possibility that the prolonged component may be due to the recruitment of caffeine-sensitive intracellular Ca 2ϩ stores.…”

Section: Discussionmentioning

confidence: 98%

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Caffeine-stimulated GTH-II release involves Ca²⁺stores with novel properties

Johnson

Wong

Yunker

et al. 2002

American Journal of Physiology-Cell Physiology

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Modulation of Ca(2+) stores with 10 mM caffeine stimulates robust secretion of gonadotropin (GTH-II) from goldfish gonadotropes. Although both endogenous forms of gonadotropin-releasing hormone (GnRH) utilize a common intracellular Ca(2+) store, sGnRH, but not cGnRH-II, uses an additional caffeine-sensitive mechanism. We examined caffeine signaling by using Ca(2+) imaging, electrophysiology, and cell-column perifusion. Although caffeine inhibited K+ channels, this action appeared to be unrelated to caffeine-induced GTH-II release, because the latter was insensitive to tetraethylammonium. The effects of caffeine also were not mediated by the cAMP/protein kinase A pathway. Instead, caffeine-evoked GTH-II responses were Ca(2+) signal dependent because they were abolished by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid loading. Caffeine generated localized Ca(2+) signals that began near secretory granules. Surprisingly, caffeine-stimulated GTH-II release was insensitive to 100 microM ryanodine and, unlike GnRH action, was unaffected by inhibitors of voltage-gated Ca(2+) channels or sarco(endo)plasmic reticulum Ca(2+)-ATPases. Collectively, these data indicate that caffeine-stimulated GTH-II release is not mediated by typical agonist-sensitive Ca(2+) stores found in endoplasmic reticulum.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 98%

Caffeine-stimulated GTH-II release involves Ca²⁺stores with novel properties

Johnson

Wong

Yunker

et al. 2002

American Journal of Physiology-Cell Physiology

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“…As in the striped bass [22], T was necessary to observe the effect of GnRH. Thus, in both species, T appears to play a facilitatory role, likely by increasing pituitary sensitivity to GnRH, as it does in various teleosts [38,41,42]. Similarly, in various juvenile teleosts, GnRHa is efficacious only when administered in combination with T (for review, see [26]).…”

Section: Discussionmentioning

confidence: 97%

Dopamine Inhibits Luteinizing Hormone Synthesis and Release in the Juvenile European Eel: A Neuroendocrine Lock for the Onset of Puberty1

Vidal¹,

Pasqualini²,

Belle³

et al. 2004

Biology of Reproduction

157

113

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In various adult teleost fishes, LH ovulatory peak is under a dual neurohormonal control that is stimulatory by GnRH and inhibitory by dopamine (DA). We investigated whether DA could also be involved in the inhibitory control of LH at earlier steps of gametogenesis by studying the model of the European eel, Anguilla anguilla, which remains at a prepubertal stage until the oceanic reproductive migration. According to a protocol previously developed in the striped bass, eels received sustained treatments with GnRH agonist (GnRHa), DA-receptor antagonist (pimozide), and testosterone (T) either alone or in combination. Only the triple treatment with T, GnRHa, and pimozide could trigger dramatic increases in LH synthesis and release as well as in plasma vitellogenin levels and a stimulation of ovarian vitellogenesis. Thus, in the prepubertal eel, removal of DA inhibition is required for triggering GnRH-stimulated LH synthesis and release as well as ovarian development. To locate the anatomical support for DA inhibition, the distribution of tyrosine hydroxylase (TH) in the brain and pituitary was studied by immunocytochemistry. Numerous TH-immunoreactive cell bodies were observed in the preoptic anteroventral nucleus, with a dense tract of immunoreactive fibers reaching the pituitary proximal pars distalis, where the gonadotrophs are located. This pathway corresponds to that mediating the inhibition of LH and ovulation in adult teleosts. To our knowledge, this is the first demonstration of a pivotal role for DA in the control of LH and puberty in a juvenile teleost. These data support the view that DA inhibition on LH secretion is an ancient evolutionary component in the neuroendocrine regulation of reproduction that may have been partially maintained throughout vertebrate evolution.

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“…For example, seasonal differences in the direct gonadal feedback influences on sGnRH, and cGnRH-II stimulation of hormone release from gonadotropes, may be manifested through differential actions at the level of these intracellular signaling systems (Lo et al 1998b). In addition, sGnRH has been shown to be more consistently effective in elevating GTH-II beta-subunit mRNA levels than cGnRH-II in the goldfish pituitary (Khakoo et al 1994).…”

Section: Summary Perspectives and Physiological Implicationsmentioning

confidence: 98%

Signal transduction mechanisms mediating secretion in goldfish gonadotropes and somatotropes

Chang

Johnson²,

Goor³

et al. 2000

Biochem. Cell Biol.

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The intracellular signal transduction mechanisms mediating maturational gonadotropin and somatotropin secretion in goldfish are reviewed. Several major signaling mechanisms, including changes in intracellular [Ca2+], arachidonic acid cascades, protein kinase C, cyclic AMP/protein kinase A, calmodulin, nitric oxide, and Na+/H+ antiport, are functional in both cell types. However, their relative importance in mediating basal secretion and neuroendocrine-factor-regulated hormone release differs according to cell type. Similarly, agonist- and cell-type-specificity are also present in the transduction pathways leading to neuroendocrine factor-modulated maturational gonadotropin and somatotropin release. Specificity is present not only in the actions of different regulators within the same cell type and with the same ligand in the two cell types, but this also exists between isoforms of the same neuroendocrine factor within a single cell type. Other evidence suggests that function-selectivity of signaling may also result from differential modulation of Ca2+ fluxes from different sources. The interaction of different second messenger systems provide the basis by which regulation of maturational gonadotropin and somatotropin release by multiple neuroendocrine factors can be integrated at the target cell level.

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In VitroApplication of Testosterone Potentiates Gonadotropin-Releasing Hormone-Stimulated Gonadotropin-II Secretion from Cultured Goldfish Pituitary Cells

Cited by 18 publications

References 43 publications

Caffeine-stimulated GTH-II release involves Ca²⁺stores with novel properties

Caffeine-stimulated GTH-II release involves Ca²⁺stores with novel properties

Dopamine Inhibits Luteinizing Hormone Synthesis and Release in the Juvenile European Eel: A Neuroendocrine Lock for the Onset of Puberty1

Signal transduction mechanisms mediating secretion in goldfish gonadotropes and somatotropes

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In VitroApplication of Testosterone Potentiates Gonadotropin-Releasing Hormone-Stimulated Gonadotropin-II Secretion from Cultured Goldfish Pituitary Cells

Cited by 18 publications

References 43 publications

Caffeine-stimulated GTH-II release involves Ca2+stores with novel properties

Caffeine-stimulated GTH-II release involves Ca2+stores with novel properties

Dopamine Inhibits Luteinizing Hormone Synthesis and Release in the Juvenile European Eel: A Neuroendocrine Lock for the Onset of Puberty1

Signal transduction mechanisms mediating secretion in goldfish gonadotropes and somatotropes

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Caffeine-stimulated GTH-II release involves Ca²⁺stores with novel properties

Caffeine-stimulated GTH-II release involves Ca²⁺stores with novel properties