Melatonin stimulates the release of growth hormone and prolactin by a possible induction of the expression of frog growth hormone-releasing peptide and its related peptide-2 in the amphibian hypothalamus

Vishwajit S. Chowdhury, Kazutoshi Yamamoto, Izumi Saeki, Itaru Hasunuma, Taichi Shimura, Kazuyoshi Tsutsui

    Research output: Contribution to journalArticle

    9 Citations (Scopus)

    Abstract

    We recently identified a novel hypothalamic neuropeptide stimulating GH release in bullfrogs and termed it frog GH-releasing peptide (fGRP). The fGRP precursor encodes fGRP and its related peptides (fGRP-RP-1, -RP-2, and -RP-3), and fGRP-RP-2 also stimulates GH and prolactin (PRL) release. Cell bodies and terminals containing these neuropeptides are localized in the suprachiasmatic nucleus (SCN) and median eminence, respectively. To understand the physiological role of fGRP and fGRP-RP-2, we investigated the mechanisms that regulate the expression of these neuropeptides. This study shows that melatonin induces the expression of fGRP and fGRP-RPs in bullfrogs. Orbital enucleation combined with pinealectomy (Ex plus Px) decreased the expression of fGRP precursor mRNA and content of mature fGRP and fGRP-RPs in the diencephalon including the SCN and median eminence. Conversely, melatonin administration to Ex plus Px bullfrogs increased dose-dependently their expressions. The expression of fGRP precursor mRNA was photoperiodically controlled and increased under short-day photoperiods,whenthe nocturnal duration of melatonin secretion increases. To clarify the mode of melatonin action on the induction of fGRP and fGRP-RPs, we further demonstrated the expression of Mel1b, a melatonin receptor subtype, in SCN neurons expressing fGRP precursor mRNA. Finally, we investigated circulating GH and PRL levels after melatonin manipulation because fGRP and fGRP-RP-2 stimulate the release of GH and GH/PRL, respectively. Ex plus Px decreased plasma GH and PRL concentrations, whereas melatonin administration increased these hormone levels. These results suggest that melatonin induces the expression of fGRP and fGRP-RP-2, thus stimulating the release of GH and PRL in bullfrogs.

    Original languageEnglish
    Pages (from-to)962-970
    Number of pages9
    JournalEndocrinology
    Volume149
    Issue number3
    DOIs
    Publication statusPublished - 2008 Mar

    Fingerprint

    Amphibians
    Melatonin
    Anura
    Prolactin
    Growth Hormone
    Hypothalamus
    Peptides
    Rana catesbeiana
    Suprachiasmatic Nucleus
    RNA Precursors
    Neuropeptides
    gamma-aminobutyryl-2-methyltryptophyl-2-methyltryptophyl-2-methyltryptophyl-lysinamide
    Median Eminence
    Melatonin Receptors
    Diencephalon
    Photoperiod

    ASJC Scopus subject areas

    • Endocrinology
    • Endocrinology, Diabetes and Metabolism

    Cite this

    Melatonin stimulates the release of growth hormone and prolactin by a possible induction of the expression of frog growth hormone-releasing peptide and its related peptide-2 in the amphibian hypothalamus. / Chowdhury, Vishwajit S.; Yamamoto, Kazutoshi; Saeki, Izumi; Hasunuma, Itaru; Shimura, Taichi; Tsutsui, Kazuyoshi.

    In: Endocrinology, Vol. 149, No. 3, 03.2008, p. 962-970.

    Research output: Contribution to journalArticle

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    abstract = "We recently identified a novel hypothalamic neuropeptide stimulating GH release in bullfrogs and termed it frog GH-releasing peptide (fGRP). The fGRP precursor encodes fGRP and its related peptides (fGRP-RP-1, -RP-2, and -RP-3), and fGRP-RP-2 also stimulates GH and prolactin (PRL) release. Cell bodies and terminals containing these neuropeptides are localized in the suprachiasmatic nucleus (SCN) and median eminence, respectively. To understand the physiological role of fGRP and fGRP-RP-2, we investigated the mechanisms that regulate the expression of these neuropeptides. This study shows that melatonin induces the expression of fGRP and fGRP-RPs in bullfrogs. Orbital enucleation combined with pinealectomy (Ex plus Px) decreased the expression of fGRP precursor mRNA and content of mature fGRP and fGRP-RPs in the diencephalon including the SCN and median eminence. Conversely, melatonin administration to Ex plus Px bullfrogs increased dose-dependently their expressions. The expression of fGRP precursor mRNA was photoperiodically controlled and increased under short-day photoperiods,whenthe nocturnal duration of melatonin secretion increases. To clarify the mode of melatonin action on the induction of fGRP and fGRP-RPs, we further demonstrated the expression of Mel1b, a melatonin receptor subtype, in SCN neurons expressing fGRP precursor mRNA. Finally, we investigated circulating GH and PRL levels after melatonin manipulation because fGRP and fGRP-RP-2 stimulate the release of GH and GH/PRL, respectively. Ex plus Px decreased plasma GH and PRL concentrations, whereas melatonin administration increased these hormone levels. These results suggest that melatonin induces the expression of fGRP and fGRP-RP-2, thus stimulating the release of GH and PRL in bullfrogs.",
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    AU - Hasunuma, Itaru

    AU - Shimura, Taichi

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