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Melatonin: reproductive effects.

R J Reiter, M D Rollag, E S Panke

    Journal of Neural Transmission. Supplementum
    |January 1, 1978
    PubMed
    Summary
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    Melatonin, a hormone from the pineal gland, also originates elsewhere. It regulates reproductive physiology in Syrian hamsters, especially when administered during specific light phases.

    Area of Science:

    • Endocrinology
    • Neuroscience
    • Reproductive Biology

    Background:

    • Melatonin (N-acetyl-5-methoxytryptamine) is primarily synthesized and secreted by the pineal gland.
    • Blood melatonin levels decrease but do not disappear after pinealectomy, suggesting extra-pineal sources like the retinas, Harderian glands, and gastro-intestinal tract.
    • Melatonin's synthesis and secretion are linked to light-dark cycles.

    Purpose of the Study:

    • To investigate the antigonadotrophic effects of melatonin in Syrian hamsters.
    • To determine the critical timing for melatonin's action on reproductive physiology.
    • To explore the impact of continuous melatonin availability on reproductive function.

    Main Methods:

    • Administering melatonin acutely at different times during the light-dark cycle to Syrian hamsters.

    Related Experiment Videos

  • Surgically removing the pineal gland to observe changes in blood melatonin levels.
  • Providing continuous melatonin availability via subcutaneous deposits in light-restricted or blinded hamsters.

    • Main Results:

    • Acute melatonin administration demonstrated potent antigonadotrophic action only during a specific late-light phase period.
    • Melatonin administered outside this sensitive period had minimal impact on hamster reproductive physiology.
    • Continuous melatonin availability counteracted the antigonadotrophic effects of the pineal gland in manipulated hamsters, inducing a 'functional pinealectomy'.
    • Chronically available melatonin abolished the antigonadotrophic effects of acute melatonin injections.

    Conclusions:

    • Melatonin's reproductive effects are highly dependent on the timing of administration relative to the light-dark cycle.
    • Extra-pineal sources contribute to circulating melatonin levels.
    • Continuous melatonin availability can override the influence of the pineal gland and acute melatonin signals on reproductive physiology.