Thyroid hormones in grey seal pups (Halichoerus grypus)

Area of Science:

• Marine Mammal Endocrinology
• Seal Physiology
• Thyroid Hormone Dynamics

Background:

• Thyroid hormones are critical for metabolism, growth, and development in mammals.
• Understanding thyroid hormone status in marine mammals is essential for assessing their health and environmental adaptation.
• Grey seal pups undergo rapid physiological changes from birth to weaning, necessitating investigation into their endocrine system.

Purpose of the Study:

• To characterize the developmental changes in thyroid hormone concentrations (total thyroxine, free thyroxine, and total triiodothyronine) in grey seal pups.
• To establish reference ranges for thyroid hormone status in young grey seals.
• To provide a baseline for future studies investigating the effects of environmental contaminants on thyroid function in seals.

Main Methods:

• Longitudinal sampling of plasma from grey seal pups from birth through weaning and moulting.
• Quantification of plasma total thyroxine (tT4), total triiodothyronine (tT3), and free thyroxine (fT4) concentrations.
• Statistical analysis to determine age-related changes and patterns in hormone levels.

Main Results:

• Plasma total thyroxine (tT4) peaked in the first two days postpartum, then stabilized at a lower level.
• Plasma total triiodothyronine (tT3) concentrations increased with age, suggesting enhanced T4 to T3 conversion.
• Free thyroxine (fT4) levels remained constant with age; all hormone levels were higher than in adult seals.

Conclusions:

• Thyroid hormone profiles in grey seal pups differ significantly from adults, reflecting high metabolic demands for growth and development.
• The observed patterns suggest maternal transfer and age-dependent T4 deiodination are key factors.
• This study establishes vital reference data for thyroid hormone status in a pristine grey seal population, crucial for comparative toxicological studies.