ADRENOCORTICAL FUNCTION IN PINNIPED HYPONATREMIA

Authors

  • D. J. St. Aubin,

    1. Wildlife Section, Department of Pathology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
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    • 1

      R. Elsner served as guest editor for the review of this paper, which was published during J. Geraci's tenure as Journal editor.

  • J. R. Geraci

    1. Wildlife Section, Department of Pathology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
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Abstract

Potentially fatal sodium imbalance occurs in captive and free-ranging pinnipeds and is associated with a variety of stressors. We sought to determine the role of adrenal hormones, principally aldosterone, in the development of this condition. To induce hyponatremia, two ringed seals, Phoca hispida, were maintained in fresh water and fed a low-sodium diet; as controls, two other ringed seals were held in salt water and received a salt-supplemented diet. After 3–6 mo, adrenocorticotropic hormone (ACTH) was used to assess adrenocortical function. In normonatremic control seals, ACTH produced a 2-j-fold increase in circulating cortisol and a 7-fold increase in aldosterone. One of the experimental seals maintained normal plasma sodium levels, and ACTH elicited an exaggerated aldosterone response. The other salt-deprived seal became hypo-natremic, and ACTH had little effect on plasma aldosterone levels. An ACTH stimulation test performed on a spontaneously hyponatremic harp seal, P. groenlandica, which had been maintained in a salt-rich environment, failed to elicit cortisol or aldosterone secretion from the adrenal cortex. This study demonstrated the unusual sensitivity of the seal's zona glomerulosa to central stimulation, providing a mechanism through which the stress response might exhaust adrenal hormone reserves or desensitize the cortex to other physiological stimuli.

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