Abstract Northern elephant seal ( Mirounga angustirostris ) pups rely on the oxidation of fat stores as their primary source of energy during their 8- to 12-wk postweaning fast; however, potential endocrine mechanisms involved with this increased fat metabolism have yet to be examined. Therefore, 15 pups were serially blood sampled in the field during the first 7 wk of their postweaning fast to examine the changes in plasma concentrations of cortisol and thyroid hormones (TH), which are involved in fat metabolism in other mammals. Cortisol increased, indicating that it contributed to an increase in lipolysis. Increased total triiodothyronine (tT 3 ) and thyroxine (tT 4 ) may not reflect increased thyroid gland activity, but rather alterations in hormone metabolism. tT 3 -to-tT 4 ratio decreased, suggesting a decrease in thyroxine (T 4 ) deiodination, whereas the negative correlation between total proteins and free T 4 suggests that the increase in free hormone is attributed to a decrease in binding globulins. Changes in TH are most similar to those observed during hibernation than starvation in mammals, suggesting that the metabolic adaptations to natural fasting are more similar to hibernation despite the fact these animals remain active throughout the fasting period. fat metabolism food deprivation leptin marine mammals Footnotes This research was supported by National Institutes of Health Minority Access to Research Careers Grant GM 58903–01 (C. L. Ortiz), National Aeronautics and Space Administration (NASA) Graduate Student Research Program NGT-2–52230 (R. M. Ortiz), and NASA Grants 121–10–50 and 121–40–10 (C. E. Wade). This research was conducted in partial fulfillment of the requirements for the doctorate degree in biology for R. M. Ortiz. Research was conducted under National Marine Fisheries Service marine mammal permit #836 to C. L. Ortiz and UCSC Chancellor's Animal Research Committee permit Orti89.08 to C. L. Ortiz and R. M. Ortiz. Address for reprint requests and other correspondence: R. M. Ortiz (E-mail: email@example.com ). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “ advertisement ” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Copyright © 2001 the American Physiological Society
AJP - Regulatory, Integrative and Comparative Physiology – The American Physiological Society
Published: Mar 1, 2001
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