Angiotensin II and Aldosterone Increase with Fasting in Breeding Adult Male Northern Elephant Seals ( Mirounga angustirostris )

Department of Biology, University of California, Santa Cruz, California, 95064, USA.
Physiological and Biochemical Zoology (Impact Factor: 2.4). 11/2006; 79(6):1106-12. DOI: 10.1086/505996
Source: PubMed


The renin-angiotensin-aldosterone system (RAAS) appears to contribute significantly to osmoregulation of fasting northern elephant seal (Mirounga angustirostris) pups; however, RAAS has not been characterized in fasting adult seals. Therefore, this study examined the contribution of RAAS to water turnover rates in fasting adult male northern elephant seals. Blood samples were obtained twice during their breeding fast at an interval of 6.5 wk, and water efflux rate was estimated by isotopic dilution during the same period. Serum electrolytes (Na+, K+, Cl-) and osmolality were unaltered between the two sampling periods, indicating ionic and osmotic homeostasis during the fast. Despite the lack of an increase in vasopressin, serum angiotensin II and aldosterone were increased and were significantly and positively correlated. Changes in aldosterone concentration and water efflux rate were significantly and negatively correlated, suggesting that the greater the increase in aldosterone, the smaller the loss of water. Adult male seals maintain ionic and osmotic homeostasis similar to that of fasting weaned pups, and this homeostasis appears to be mediated, at least in part, by RAAS, which probably contributes to increased water retention as well. The hormonal mechanisms by which northern elephant seals maintain water and electrolyte balance during fasting conditions appear to be similar regardless of age.

Download full-text


Available from: Daniel E Crocker
  • Source
    • "This suggests that potential lipolytic benefits of elevations in cortisol (Crocker et al., 2014) are secondary to other impacts on metabolism, including protein sparing. In contrast, aldosterone concentrations increased across the fast (Ortiz et al., 2006), which may support the hypothesis that aldosterone is an important factor in the stress response (in this case, prolonged nutrient deprivation). Here we report changes in adrenal, thyroid and sex hormones, as well as key metabolites, in response to an ACTH challenge in breeding and molting adult male northern elephant seals. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Strong individual and life-history variation in serum glucocorticoids has been documented in many wildlife species. Less is known about variation in hypothalamic-pituitary-adrenal (HPA) axis responsiveness and its impact on metabolism. We challenged 18 free-ranging adult male northern elephant seals (NES) with an intramuscular injection of slow-release adrenocorticotropic hormone (ACTH) over 3 sample periods: early in the breeding season, after 70+ days of the breeding fast, and during peak molt. Subjects were blood sampled every 30 minutes for 2 hrs post-injection. Breeding animals were recaptured and sampled at 48 hrs. In response to the ACTH injection, cortisol increased 4-6 fold in all groups, and remained elevated at 48 hrs in early breeding subjects. ACTH was a strong secretagogue for aldosterone, causing a 3-8 fold increase in concentration. Cortisol and aldosterone responses did not vary between groups but were correlated within individuals. The ACTH challenge produced elevations in plasma glucose during late breeding and molting, suppressed testosterone and thyroid hormone at 48 hrs in early breeding, and increased plasma non-esterified fatty acids and ketoacids during molting. These data suggest that sensitivity of the HPA axis is maintained but the metabolic impacts of cortisol and feedback inhibition of the axis vary with life history stage. Strong impacts on testosterone and thyroid hormone suggest the importance of maintaining low cortisol levels during the breeding fast. These data suggest that metabolic adaptations to extended fasting in NES include alterations in tissue responses to hormones that mitigate deleterious impacts of acute or moderately sustained stress responses.
    Full-text · Article · Aug 2014 · General and Comparative Endocrinology
  • Source
    • "These previous studies were based on longitudinal sampling during periods of experimental food restriction or fasting in juvenile and sub-adult SSL. Further, periods of natural fasting were associated with an increase in aldosterone concentrations in phocids [45] [48]. Given the high energy demand and rapid growth (0.23– 0.48 kg/day) during the postnatal period of SSL pups [10], we expected an association between BCI and circulating concentrations of a suite of hormones associated with nutritional status and fat mass, lipid and water metabolism, and/or growth and metabolism. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Body condition indices have been useful in assessing the health of domestic and free ranging populations of terrestrial mammals. Given the high energy demand and rapid growth during the postnatal period of Steller sea lion (Eumetopias jubatus) (SSL) pups, body condition was expected to be related to concentrations of a suite of hormones (cortisol, aldosterone, thyroxine, triiodothyronine, leptin) previously associated with changes in body mass and composition in developing pinnipeds. Blood samples were collected from free ranging SSL pups of known ages and sex. A body condition index (BCI) previously developed for SSL pups based on a mass and length relationship was applied to 61 SSL pups ranging in age from 5 to 38 days old. BCI was not related to pup age. Overall, male pups were larger than females and older pups were larger than younger pups. Aldosterone was negatively correlated with BCI only in female pups, whereas no relationship was observed between aldosterone and BCI in males. Further, male pups had higher aldosterone concentrations than females. Concentrations of cortisol, total and free thyroxine (T(4)), and total triiodothyronine (T(3)) decreased when regressed against the elapsed time between researchers' arrival on the rookery and removal of pup from the holding corral for blood collection. While the overall variation attributed to the rookery disturbance was low (r(2)<0.293), it may be of significance for future studies on free ranging pinnipeds. This study adds to the current knowledge of the postnatal changes in free ranging SSL pups by providing ranges of the BCI and several hormone concentrations from an apparently stable population.
    Full-text · Article · Jan 2013 · General and Comparative Endocrinology
  • Source
    • "Males compete for position in a dominance hierarchy used to control access to estrus females (Le Boeuf, 1974; Haley et al., 1994) while fasting from food and water, losing ~36% of their arrival body mass over a 3-month period (Deutsch et al., 1994; Crocker et al., 2012). During this period, males have low rates of water flux and spare protein efficiently (Ortiz et al., 2006; Crocker et al., 2012). Studies in fasting and lactating female elephant seals have suggested reduced insulin response and sensitivity (Fowler et al., 2008; Viscarra et al., 2011a, 2011b). "
    [Show abstract] [Hide abstract]
    ABSTRACT: We measured metabolic hormones and several key metabolites in breeding adult male northern elephant seals to examine the regulation of fuel metabolism during extended natural fasts of over 3 months associated with high levels of energy expenditure. Males were sampled twice, early and late in the fast, losing an average of 23% of body mass and 47% of adipose stores between measurements. Males exhibited metabolic homeostasis over the breeding fast with no changes in glucose, non-esterified fatty acids, or blood urea nitrogen. Ketoacids increased over the fast but were very low when compared to other fasting species. Changes within individuals in total triiodothyronine (tT(3)) were positively related to daily energy expenditure (DEE) and protein catabolism. Differences in levels of thyroid hormones relative to that observed in weaned pups and females suggest a greater deiodination of T(4) to support the high DEE of breeding males. Relative levels of leptin and ghrelin were consistent with the suppression of appetite but a significant reduction in growth hormone across the fast was contrary to expectation in fasting mammals. The lack of the increase in cortisol during fasting found in conspecific weaned pups and lactating females may contribute to the ability of breeding males to spare protein despite high levels of energy expenditure. Together these findings reveal significant differences with conspecifics under varying nutrient demands, suggesting metabolic adaptation to extended high energy fasts.
    Full-text · Article · Apr 2012 · Comparative biochemistry and physiology. Part A, Molecular & integrative physiology
Show more