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*

*この研究の対応する著者

    研究成果: Article査読

    9 被引用数 (Scopus)

    抄録

    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.

    本文言語English
    ページ(範囲)962-970
    ページ数9
    ジャーナルEndocrinology
    149
    3
    DOI
    出版ステータスPublished - 2008 3月

    ASJC Scopus subject areas

    • 内分泌学
    • 内分泌学、糖尿病および代謝内科学

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