Meeting Abstract

P1.141  Saturday, Jan. 4 15:30  Effects of an acute stimulation of the HPA axis on sexual and stress hormones in male Northern Elephant Seals ENSMINGER, D.C.*; SHARICK, J.T.; SOMO, D.A.; HOUSER, D.S.; CROCKER, D.E.; Sonoma State University, California, Rohnert Park ensminge@seawolf.sonoma.edu

Little is known about variations in hypothalamic-pituitary-axis (HPA) responsiveness and its impacts on metabolism in wild pinnipeds. To characterize changes due to acute stress, 18 free living adult male northern elephant seals were challenged with an intramuscular injection of slow release adrenocorticotropic hormone (ACTH) over 3 sample periods: early in the breeding season, after 70+ days of the breeding fast and during peak molt. Subjects were blood sampled every 30 minutes for 2 hrs post-injection. Breeding animals were recaptured and sampled at 48 hrs. This was not possible in molting subjects due to animal density and mobility. In response to ACTH, cortisol increased two-three fold in all groups, and remained elevated at 48 hrs in early breeding subjects. ACTH was a stronger secretagogue for aldosterone, causing a three-eight fold increase. Cortisol and aldosterone responses did not vary between groups but were significantly correlated among individuals. Endogenous ACTH was suppressed by the challenge in late breeding males, particularly at 48 hrs. Cortisol increases resulted in elevations in plasma glucose only during molting. ACTH challenge caused suppression of testosterone and thyroid hormone (T3) at 48 hrs in early breeding males. ACTH challenge increased plasma non-esterified fatty acids and blood urea nitrogen in all study groups. These data suggest that sensitivity of the HPA axis is maintained but the metabolic impacts of cortisol and feedback inhibition of the axis varies with life history stage. Strong impacts of the challenge on testosterone, thyroid hormone and protein sparing suggest the importance of maintaining low cortisol levels during breeding.