Adrenal Response to Stimulation by Adrenocorticotropic Hormone (ACTH) in Captive Northern Fur Seals, Callorhinus ursinus

Abstract

The effect of adrenocorticotrophic hormone (ACTH) on circulating hormones and leukocytes were examined in six adult (2M, 4F) northern fur seals, Callorhinus ursinus. A control study using physiological saline was carried out on two of the female fur seals. Blood samples were taken prior to injection, and at 8 time periods following i.m. injection with saline or 10-28 IU ACTH (0.215-0.306 IU/kg). Stimulation by ACTH caused an elevation of both cortisol and aldosterone levels, along with an increase in neutrophile and a decrease in lymphocytes and eosinophils. Peak times for cortisol were within 3h after stimulation and aldosterone peaked within 1.5h. In contrast to the characteristic response to ACTH by terrestrial mammals, aldosterone peaks were relatively greater than cortisol peaks, a pattern similar found in studies of other marine mammals. The results of this study suggest a common adaptation in the stress response of marine mammals