Meeting Abstract
Understanding how marine mammals respond physiologically to anthropogenic stressors can inform marine ecosystem conservation strategies. Stress stimulates release of glucocorticoid (GC) hormones, which increase energy substrate availability while suppressing energy-intensive processes. Exposure to repeated stressors potentially affect an animal’s ability to respond to and recover from subsequent challenges. To assess the endocrine response of the elephant seal (Mirounga angustirostris) to repeated stressors, we administered adrenocorticotropic hormone (ACTH) to juvenile seals (n=7) once daily for four days. ACTH administrations induced significant, transient (lasting <24 h) elevations in circulating cortisol (p < 0.0001). These increases did not vary in magnitude between day 1 and day 4. In contrast, aldosterone levels remained elevated above baseline for at least 24 hours after each ACTH injection (p < 0.001), with responses being greater on day 4 (p < 0.01). Total triiodothyronine (T3) levels were decreased on day 4 (p < 0.01), while reverse triiodothyronine (rT3) concentrations increased relative to baseline on days 1 and 4 (p < 0.001), indicating potential metabolic suppression. These data suggest that repeated stress results in facilitation of aldosterone secretion and suppression of total T3, which may have long-term physiological impacts. However, this did not seem to impair the seals’ ability to mount an adrenal response to each ACTH challenge. We propose that aldosterone may be a more informative indicator of repeated stress exposure than cortisol in some marine mammals.
