ADRENOCORTICAL FUNCTION IN PINNIPED HYPONATREMIA |
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Authors: | D J St Aubin J R Geraci |
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Institution: | 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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Keywords: | pinnipeds sodium balance aldosterone cortisol hyponatremia adrenocorticotropic hormone adrenal zona glomerulosa stress |
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