Abstract
Thyroid hormones play a critical physiological role in regulating protein synthesis and metabolism. Secretion is primarily regulated via negative-feedback control through the coordinated response of the hypothalamic-pituitary-thyroid axis.1 Any dysfunction along this axis may result in thyroid hormone abnormalities that could have profound consequences on proper physiological function and animal health.1 Proper interpretation of hormonal analysis in cetaceans must be based on an understanding of the environmental and biological influences surrounding their endocrine cycles.2 Previous studies have been completed using wild and semi-domesticated Atlantic bottlenose dolphins (Tursiops truncatus) but few studies have been published on thyroid hormones in aquarium-maintained or wild belugas.2-4 The current study examines variations in thyroid hormone values (T4, thyroxine; T3, triiodothyronine; TSH, thyroid stimulating hormone) in healthy aquarium-maintained and wild beluga whales and documents differences associated with biological and environmental influences including age, sex, and seasonality. Serum concentrations of T4, T3, and TSH were determined by competitive immunoassay using chemiluminescence in 22 aquarium-maintained belugas (12 females and 10 males) and 39 wild belugas from two Alaskan populations. All values are reported as mean ± standard error and significance is reported at p < 0.05. T4 concentrations in aquarium-maintained belugas were 4.95 ± 0.33 µg/dl, T3 concentrations were 58.24 ± 2.43 ng/dl, and TSH levels were 0.029 ± 0.002 IU/L. Sex comparisons showed that aquarium held females exhibited significantly greater T3 concentrations then males (62.7 ± 3.1 ng/dl vs. 51.7 ± 2.6 ng/dl respectively); males and females did not differ significantly in T4 or TSH levels. Age class comparisons showed that male aquarium held belugas exhibited significant variation in T4 concentrations among age classes while females showed significant variation in TSH among age classes. Although significant differences were noted among age classes there is no simple linear relationship between thyroid hormone levels and age of male and female beluga whales. Seasonal analysis of thyroid hormone showed that T4 concentrations varied significantly across seasons in aquarium held belugas with highest levels in the summer and fall (5.42 ± 0.36 µg/dl and 5.29 ± 0.37 µg/dl, respectively) and lowest levels in winter and spring (4.45 ± 0.32 µg/dl and 4.62 ± 0.34 µg/dl, respectively). T3 and TSH exhibited no significant variation across seasons. Comparisons of aquarium-maintained and wild populations showed that T4 and T3 levels were higher in wild beluga populations then in aquarium-maintained animals. TSH levels did not differ significantly between groups. In wild belugas, T4 concentrations were 11.38 ± 0.56 µg/dl, T3 concentrations were 108.88 ± 3.92 ng/dl, and TSH levels were 0.02 ± 0.001 IU/L. Additional sample analysis is ongoing in both wild and aquarium-maintained belugas in order to better represent age, sex, and seasonal variability. The findings of this study provide a baseline for future thyroid health monitoring and comprehensive health assessments in aquarium-maintained and wild beluga whales.
Acknowledgments
This project would not have been possible without the support and contributions of the following people and organizations: Dr. Karen Wolfe and Julie Lemon from Point Defiance Zoo and Aquarium, Dr. Marty Haulena and Chelsea DeColle from Vancouver Aquarium, Dr. Tonya Clauss, Dr. Al Dove, Harry Webb, and Nicole LaBove from Georgia Aquarium, Dr. Paul Calle, Kate McClave, and Dee McAloose from the Wildlife Conservation Society, Dr. Caryn Poll and Mayela Alsina-Guerrero from the John G. Shedd Aquarium, and Dr. Roderick Hobbs from NOAA/NMFS/NMML. We are also grateful to Amy Delmonaco and Gayle Sirpenski at Mystic Aquarium for their assistance.
References
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