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

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press ABSTRACTThe 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 ϩ , K ϩ , Cl Ϫ ) 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.

Metabolic responses to adrenocorticotropic hormone (ACTH) vary with life-history stage in adult male northern elephant seals

“…This suggests that potential lipolytic benefits of elevations in cortisol [44] are secondary to other impacts on metabolism, including protein sparing. In contrast, aldosterone concentrations increased across the fast [45], which may support the hypothesis that aldosterone is an important factor in the stress response (in this case, prolonged nutrient deprivation).…”

“…Aldosterone response to ACTH was highest during late breeding when baseline aldosterone levels are highest. This suggests that pituitary stimulation may contribute independently to the strong upregulation of the RAS system seen across fasting [45]. The elevation of aldosterone had no significant effect on the electrolytes Na+ and K +.…”

“…Angiotensin II can induce peripheral vasoconstriction [64][65][66], which may be beneficial to diving marine mammals experiencing acute stressors, but which may also result in an increase in aldosterone production. While increases in aldosterone can be beneficial in a fasting state due to decreased efflux of water and reabsorption of Na+, it could also be a detrimental response in a hyperosmotic environment such as the ocean [45,67,68].Thus, it may not be surprising that the aldosterone response showed strong negative feedback in all breeding groups suggesting a reduced response to sustained stress. Aldosterone response to ACTH was highest during late breeding when baseline aldosterone levels are highest.…”

Variation in adrenal and thyroid hormones with life-history stage in juvenile northern elephant seals (Mirounga angustirostris)

“…The regulation of aldosterone release by the HPA axis may reflect the need to alter kidney perfusion and lung perfusion during diving, inhibiting typical RAS regulation (Atkinson et al, 2015). In contrast to the juveniles in the current study, aldosterone concentrations increased across the breeding fast in adult male elephant seals (Champagne et al, 2006;Ortiz et al, 2006) in association with RAS activation suggesting that this hormone may be under dual regulation by the HPA axis and RAS.…”

Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris)

“…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 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, 2011aViscarra et al, , 2011b.…”