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Related Experiment Videos

Pineal and thyroid functions in newborn seals

K A Stokkan1, M K Vaughan, R J Reiter

  • 1Department of Arctic Biology, University of Tromsø, Norway.

General and Comparative Endocrinology
|June 1, 1995
PubMed
Summary

Newborn seals show high pineal gland activity and elevated thyroid hormones, possibly for thermoregulation and related to diving behaviors. Melatonin rhythms were observed in plasma, but not consistently in pineal glands.

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Area of Science:

  • Marine Mammal Physiology
  • Endocrinology
  • Circadian Rhythms

Background:

  • The pineal gland produces melatonin, a hormone involved in regulating circadian rhythms and other physiological processes.
  • Thyroid hormones (T4 and T3) are crucial for metabolism and thermoregulation, especially in developing mammals.
  • Pinnipeds, like seals, exhibit unique physiological adaptations to their marine environment, including thermoregulation challenges.

Purpose of the Study:

  • To investigate daily variations in pineal and plasma melatonin and plasma thyroid hormones in newborn harp, grey, and hooded seals.
  • To examine age-related changes in these hormones within the first 14 days of life.
  • To explore potential roles of the pineal gland and thyroid hormones in seal pup physiology, including thermoregulation and diving adaptations.

Main Methods:

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  • Collected blood samples to measure plasma melatonin, thyroxine (T4), and triiodothyronine (T3) levels.
  • Assessed pineal gland mass and melatonin content in newborn seals.
  • Measured pineal beta-adrenergic receptors in harp seals.
  • Analyzed hormonal data for day-night differences, age-related trends, and 24-hour rhythmicity.

Main Results:

  • Pineal gland mass and melatonin content varied significantly among species, with hooded seals showing particularly high values.
  • Plasma melatonin levels exhibited 24-hour rhythmicity in all seal pups, with higher concentrations at night.
  • Plasma T4 and T3 levels were generally higher in newborn seals compared to older pups and adult females, declining over time without clear circadian patterns.
  • No significant day-night or age-related differences in pineal melatonin content were found in harp and grey seals.

Conclusions:

  • Newborn seals possess large and active pineal glands, suggesting a significant role for melatonin.
  • Elevated thyroid hormone levels in newborns may contribute to thermoregulation, a critical factor for survival.
  • The observed hormonal patterns suggest potential links between pineal and thyroid activity and the unique physiological demands of seal pups, including their diving habits.