Effect of Melatonin on the Release of Gonadotropin‐Releasing Hormone and Cyclic AMP from the Rat Hypothalamus: an in vitro Study

Messager, Sophie; Caillol, Monique; Rossano, Bernadette; Martinet, Lise

doi:10.1046/j.1365-2826.1996.52711.x

Cited by 9 publications

(6 citation statements)

References 38 publications

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“…HypGnRH represents 85 and 55% of the total GnRH-like content of fetal and neonatal Ht, respectively [4, 9]. The sensitivity of both peptides may thus change over time, as also suggested by the fact that cAMP- and forskolin-induced GnRH secretion decreases as the animals mature [36, 37]. This is also consistent with our observation that secretion of both peptides was only weakly stimulated by a cAMP analogue or by forskolin.…”

Section: Discussionsupporting

confidence: 88%

In vitro Secretion of Gonadotropin-Releasing Hormone (GnRH) and [Hydroxyproline9]GnRH from the Rat Hypothalamus Exhibits a Differential Sensitivity to Castration and Second Messengers

Rochdi¹,

Theraulaz²,

Enjalbert³

et al. 1998

Neuroendocrinology

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The decapeptide [hydroxyproline⁹]GnRH (HypGnRH) has been characterized as an endogenous posttranslational product of the gonadotropin-releasing hormone (GnRH) precursor in a wide range of mammalian brains. Despite consistent biological effects, its secretion by the hypothalamus remains hypothetical. We report here in vitro secretion of HypGnRH and GnRH by the hypothalamus from intact and castrated male rats and provide evidence that they are differentially regulated. Both peptides were identified by two anti-GnRH antibodies of different specificities after separation under two high-performance liquid chromatography conditions. Calcium dependency of HypGnRH release was demonstrated under stimulation with KCl in the absence or presence of Ca²⁺, as well as with Bay K 8644, veratridine, methoxyverapamil, or tetrodotoxin. Activation of signaling pathways involving adenylate cyclase and protein kinases A and C (PKC) induced HypGnRH release. Expression of data as percentage of release over tissue stores revealed a two- to threefold higher release of HypGnRH than of GnRH under the different modes of stimulation used, except under PKC activation which triggered a comparable recruitment of both peptides. Castration selectively affected PKC-coupled GnRH secretion which showed a twofold lesser release than in intact rats, while the HypGnRH release was unaffected. We conclude that HypGnRH and GnRH are not secreted from the hypothalamus according to the same mechanisms.

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Section: Discussionsupporting

confidence: 88%

In vitro Secretion of Gonadotropin-Releasing Hormone (GnRH) and [Hydroxyproline9]GnRH from the Rat Hypothalamus Exhibits a Differential Sensitivity to Castration and Second Messengers

Rochdi¹,

Theraulaz²,

Enjalbert³

et al. 1998

Neuroendocrinology

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“…That difference in CV is unlikely to be explained by the incubation system since Rasmussen et al [37] observed a more regular periodicity using perifused human mediobasal hypothalami in vitro (CV: 35%). More recently, other authors also reported pulsatile GnRH secretion showing less variable intervals using the mediobasal hypothalamus than using preoptic explants [38] . We tend to conclude that different mechanisms of episodic GnRH secretion may coexist because pulsatility is less regular using the median eminence than using the retrochiasmatic or mediobasal hypothalamus.…”

Section: Discussionmentioning

confidence: 93%

Pulsatile Secretion of Gonadotropin-Releasing Hormone by Rat Hypothalamic Explants of GnRH Neurons without Cell Bodies

et al. 1997

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Gonadotropin-releasing hormone (GnRH) is typically secreted in a pulsatile manner. It is still unclear whether pulsatility depends on a GnRH pulse generator residing in the GnRH neurons or in other neurons. Since the cell bodies of GnRH neurons are located rostrally to the optic chiasm and the majority of GnRH terminals in the median eminence of the rat hypothalamus, we have compared GnRH secretion from individual preoptic, retrochiasmatic and median eminence explants using a static incubation system. GnRH is released from the three different types of explant in response to depolarization with veratridine or glutamate receptor stimulation using the agonist N-methyl-D-aspartate. Only the retrochiasmatic explants, however, show a characteristic pulsatile secretion of GnRH. The mean (±SD) interpulse interval is respectively 37 ± 5, 25 ± 4 and 12 ± 1 min when the fractions are collected at 7.5-, 5.0- and 2.5-min intervals. The immunocytochemically stained GnRH cell bodies are normally distributed in the preoptic explants (n = 212–420) while only 3 GnRH cell bodies can be visualized in 7 retrochiasmatic explants. Semi-quantitative RT-PCR shows that GnRH mRNA is present in the retrochiasmatic explant in a ratio of about 1:600 relative to the preoptic explant. We conclude that pulsatile GnRH secretion occurs in the virtual absence of GnRH cell bodies but does not occur from GnRH terminals in the isolated median eminence. These data further indicate that a mechanism of GnRH pulsatility is located in the retrochiasmatic hypothalamus and involves neurons different from the GnRH neurons.

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“…In the present the transmitter levels during the preparation of hypothalamic tissues, may explain why the effect of melatonin on LHRH release study, we injected melatonin ICV in order to restrict the site of its action at the suprapituitary level. The lack of effect of in vitro varied among different experimental protocols (10)(11)(12).…”

Section: Discussionmentioning

confidence: 99%

“…Concerning the regulation of gonadotropin secretion, not uniform. For example, melatonin either increased ( 10,12 ), decreased ( 12) or did not affect (11,12) LHRH output from the Trentini et al (18 ) showed that melatonin prevented the loss of LH responses to naloxone in aged female rats. Aubert et al (19) hypothalamus of adult male rats in vitro.…”

mentioning

confidence: 99%

“…Suprapituitary sites of melatonin action in controlling LH suggesting that opioids may mediate the action of melatonin. Alternatively, augmentation of the morphine analgesia by mela-secretion have also been suggested in the rat (10)(11)(12). However, the reported effects of melatonin at the hypothalamic level are tonin in mice ( 17) may suggest synergism of melatonin and opioids.…”

mentioning

confidence: 99%

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Melatonin Inhibits Naloxone‐Induced Luteinizing Hormone Release in Ovariectomized Estrogen‐Primed Rats

Akema

Chiba

Ikeda

et al. 1997

J Neuroendocrinology

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The present study aimed to examine the effect of melatonin on naloxone-induced luteinizing hormone (LH) secretion in ovariectomized estrogen-primed rats. A single intracerebroventricular (i.c.v.) injection of naloxone (mu opioid receptor blocker, 15 micrograms) or an intravenous (i.v.) injection of LH-releasing hormone (LHRH, 50 ng/kg) elicited a transient and significant increase in the serum LH concentration within 10 min. While an i.c.v. injection of 100 ng melatonin by itself did not change the basal LH release, it almost completely inhibited the naloxone-induced LH release. Melatonin (10 ng) also significantly reduced the effect of naloxone. However, an i.c.v. injection of 100 ng melatonin did not affect the LHRH-induced LH release. In separate experiments, the effect of melatonin on naloxone-induced pulsatile LH secretion was studied in estrogen-treated rats. A continuous i.v. infusion of naloxone (20 mg/kg/h) induced LH pulses in rats treated i.c.v. with saline. An i.c.v. administration of 100 ng melatonin, which by itself did not affect basal LH secretion, significantly reduced the frequency, but not the amplitude, of LH pulses induced by the naloxone infusion. These results show that melatonin has a suprapituitary site of action to inhibit naloxone-induced LH release, and suggest that melatonin has an effect in inhibiting the activity of the hypothalamic LHRH pulse generator, either directly or indirectly, in female rats.

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Effect of Melatonin on the Release of Gonadotropin‐Releasing Hormone and Cyclic AMP from the Rat Hypothalamus: an in vitro Study

Cited by 9 publications

References 38 publications

In vitro Secretion of Gonadotropin-Releasing Hormone (GnRH) and [Hydroxyproline<sup>9</sup>]GnRH from the Rat Hypothalamus Exhibits a Differential Sensitivity to Castration and Second Messengers

In vitro Secretion of Gonadotropin-Releasing Hormone (GnRH) and [Hydroxyproline<sup>9</sup>]GnRH from the Rat Hypothalamus Exhibits a Differential Sensitivity to Castration and Second Messengers

Pulsatile Secretion of Gonadotropin-Releasing Hormone by Rat Hypothalamic Explants of GnRH Neurons without Cell Bodies

Melatonin Inhibits Naloxone‐Induced Luteinizing Hormone Release in Ovariectomized Estrogen‐Primed Rats

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