Seasonal variation in thyroid morphology and secretion in the white whale, Delphinapterus leucas
Thyroid activity was examined in white whales, Delphinapterus leucas, during three phases of their annual cycle: spring migration from oceanic wintering grounds, summer occupation of an estuary in Hudson Bay, and return migration in fall. Circulating levels of thyroxine (T 4 ) and triiodothyronine (...
| Published in: | Canadian Journal of Zoology |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1989
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/z89-038 http://www.nrcresearchpress.com/doi/pdf/10.1139/z89-038 |
| Summary: | Thyroid activity was examined in white whales, Delphinapterus leucas, during three phases of their annual cycle: spring migration from oceanic wintering grounds, summer occupation of an estuary in Hudson Bay, and return migration in fall. Circulating levels of thyroxine (T 4 ) and triiodothyronine (T 3 ) were significantly higher in summer. Histologically, thyroid epithelial cells were cuboidal during spring, became columnar during summer, and reverted to a cuboidal morphology in fall, changes consistent with increased synthesis and secretion of hormones during the estuarine phase. Small follicles, abundant in spring and fall samples, were relatively less numerous in summer specimens. Occupation of warm estuaries may be an important stimulus to thyroid hormone secretion, perhaps allowing the whales to mobilize subcutaneous fat stores for somatic growth in an energetically less demanding environment. |
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