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Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons.
Gen Comp Endocrinol. 2004 Apr; 136(2):289-97.GC

Abstract

A leading hypothesis for the dramatic population decline of the Alaskan harbor seal over the last 2-3 decades have related environmental changes to a decrease in the quality or quantity of available prey. If harbor seals are experiencing some sort of nutritional stress, it is important to understand the physiological and endocrine mechanisms controlling metabolic homeostasis in this species. The purpose of this research project was to determine whether circadian patterns of cortisol and total and free thyroxine (T(4)) and triiodothyronine (T(3)) are present in the harbor seal during the summer and winter seasons, and identify how they might alter metabolic rate and maintenance of body reserves. This study was carried out at the Alaska SeaLife Center in Seward, Alaska in June 2000 and January 2001. Blood samples were obtained every 2-3 h over a 24-h period through in-dwelling catheters inserted the day before sampling. The presence of a diurnal rhythm was determined by comparing levels between ante meridian (12 am to noon) and post meridian (noon to 12 midnight) time periods. Mean daily cortisol concentrations were not significantly different between seasons, but cortisol displayed a circadian rhythm only during the summer. Mean concentrations of cortisol (51.5 ng/ml+/-20.3) in the summer hours of ante meridian differed significantly from levels in the hours of post meridian (28.5 ng/ml+/-17.4). Neither total and free T(4), nor T(3), displayed a diurnal rhythm in either season. However, tT(4), tT(3), and fT(3) levels were significantly higher in the winter than in the summer. There was no seasonal effect on fT(4) levels. The absence of a circadian rhythm of cortisol during the winter may have been a result of the limited amount of daylight as well as the continual need to produce metabolic heat as a by-product of gluconeogenesis. Higher levels of thyroid hormones in the winter indicate an adaptive mechanism to cope with the low temperatures of winter.

Authors+Show Affiliations

Oki C
CTAHR, University of Hawaii at Manoa, Honolulu, HI 96822, USA. coki@hawaii.edu
Atkinson S
No affiliation info available

MeSH

AgingAnimalsCircadian RhythmFemaleHydrocortisoneMaleSeals, EarlessSeasonsThyroxineTriiodothyronine

Pub Type(s)

Comparative Study
Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

15028534

Citation

Oki, C, and S Atkinson. "Diurnal Patterns of Cortisol and Thyroid Hormones in the Harbor Seal (Phoca Vitulina) During Summer and Winter Seasons." General and Comparative Endocrinology, vol. 136, no. 2, 2004, pp. 289-97.
Oki C, Atkinson S. Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons. Gen Comp Endocrinol. 2004;136(2):289-97.
Oki, C., & Atkinson, S. (2004). Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons. General and Comparative Endocrinology, 136(2), 289-97.
Oki C, Atkinson S. Diurnal Patterns of Cortisol and Thyroid Hormones in the Harbor Seal (Phoca Vitulina) During Summer and Winter Seasons. Gen Comp Endocrinol. 2004;136(2):289-97. PubMed PMID: 15028534.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons. AU - Oki,C, AU - Atkinson,S, PY - 2003/01/27/received PY - 2003/12/15/revised PY - 2004/01/13/accepted PY - 2004/3/19/pubmed PY - 2004/10/16/medline PY - 2004/3/19/entrez SP - 289 EP - 97 JF - General and comparative endocrinology JO - Gen Comp Endocrinol VL - 136 IS - 2 N2 - A leading hypothesis for the dramatic population decline of the Alaskan harbor seal over the last 2-3 decades have related environmental changes to a decrease in the quality or quantity of available prey. If harbor seals are experiencing some sort of nutritional stress, it is important to understand the physiological and endocrine mechanisms controlling metabolic homeostasis in this species. The purpose of this research project was to determine whether circadian patterns of cortisol and total and free thyroxine (T(4)) and triiodothyronine (T(3)) are present in the harbor seal during the summer and winter seasons, and identify how they might alter metabolic rate and maintenance of body reserves. This study was carried out at the Alaska SeaLife Center in Seward, Alaska in June 2000 and January 2001. Blood samples were obtained every 2-3 h over a 24-h period through in-dwelling catheters inserted the day before sampling. The presence of a diurnal rhythm was determined by comparing levels between ante meridian (12 am to noon) and post meridian (noon to 12 midnight) time periods. Mean daily cortisol concentrations were not significantly different between seasons, but cortisol displayed a circadian rhythm only during the summer. Mean concentrations of cortisol (51.5 ng/ml+/-20.3) in the summer hours of ante meridian differed significantly from levels in the hours of post meridian (28.5 ng/ml+/-17.4). Neither total and free T(4), nor T(3), displayed a diurnal rhythm in either season. However, tT(4), tT(3), and fT(3) levels were significantly higher in the winter than in the summer. There was no seasonal effect on fT(4) levels. The absence of a circadian rhythm of cortisol during the winter may have been a result of the limited amount of daylight as well as the continual need to produce metabolic heat as a by-product of gluconeogenesis. Higher levels of thyroid hormones in the winter indicate an adaptive mechanism to cope with the low temperatures of winter. SN - 0016-6480 UR - https://www.unboundmedicine.com/medline/citation/15028534/Diurnal_patterns_of_cortisol_and_thyroid_hormones_in_the_Harbor_seal__Phoca_vitulina__during_summer_and_winter_seasons_ DB - PRIME DP - Unbound Medicine ER -