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Melatonin prevents decrease in plasma PRL and LH levels in male hamsters exposed to a short photoperiod.

G B Cutty, B D Goldman, P Doherty

    International Journal of Andrology
    |April 1, 1981
    PubMed
    Summary

    Melatonin implants prevent reproductive system regression in male hamsters exposed to short daylight. This effect is linked to maintaining prolactin (Prl) and luteinizing hormone (LH) levels, independent of the pineal gland.

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    Area of Science:

    • Reproductive endocrinology
    • Seasonal biology
    • Neuroendocrinology

    Background:

    • Melatonin injections induce testicular regression in male hamsters.
    • Subcutaneous melatonin implants prevent short-day induced testicular regression.
    • The mechanism by which melatonin implants prevent regression is unclear.

    Purpose of the Study:

    • To investigate the role of pinealectomy and melatonin implants in preventing short-day induced reproductive regression.
    • To examine the effects of melatonin on plasma prolactin (Prl), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels.
    • To determine if melatonin directly affects testicular testosterone production.

    Main Methods:

    • Male golden hamsters were pinealectomized or sham-operated.

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  • Melatonin-filled or empty Silastic capsules were implanted subcutaneously.
  • Animals were exposed to a short photoperiod (5 L:19 D) for 9 weeks.
  • Plasma hormone levels and reproductive organ weights were measured.
  • In vitro testosterone production by testes was assessed in response to hCG and melatonin.

    • Main Results:

    • Both pinealectomy and melatonin implants prevented the decline in plasma Prl and LH, and maintained testicular and seminal vesicle weights.
    • Pinealectomized hamsters with melatonin implants had higher testicular weight and plasma Prl/LH than those with empty implants.
    • Melatonin did not directly affect testosterone production by hamster testes in vitro.

    Conclusions:

    • Melatonin implants prevent male reproductive system regression under short photoperiods.
    • This protective effect is likely mediated by preventing declines in plasma Prl and LH.
    • The effects of melatonin implants are independent of the pineal gland.