Responses of the Hypothalamopituitary Adrenal Axis and the Sympathoadrenal System to Isolation/Restraint Stress in Sheep of Different Adiposity

Abstract

There is evidence that levels of adipose tissue can influence responses of the hypothalamopituitary-adrenal (HPA) axis to stress in humans and rats but this has not been explored in sheep. Also, little is known about the sympathoadrenal responses to stress in individuals with relatively different levels of adipose tissue. We tested the hypothesis that the stress-induced activation of the HPA axis and sympathoadrenal system is lower in ovariectomized ewes with low levels of body fat (lean) than ovariectomized ewes with high levels of body fat (fat). Ewes underwent dietary manipulation for 3 months to yield a group of lean ewes (n = 7) with a mean (±SEM) live weight of 39.1 ± 0.9 kg and body fat of 8.9 ± 0.6% and fat ewes (n = 7) with a mean (±SEM) live weight of 69.0 ± 1.8 kg and body fat of 31.7 ± 3.4%. Fat ewes also had higher circulating concentrations of leptin than lean ewes. Blood samples were collected every 15 min over 8 h when no stress was imposed (control day) and on a separate day when 4 h of isolation/restraint was imposed after 4 h of pretreatment sampling (stress day). Plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol, epinephrine and norepinephrine did not change significantly over the control day and did not differ between lean and fat ewes. Stress did not affect plasma leptin levels. All stress hormones increased significantly during isolation/restraint stress. The ACTH, cortisol and epinephrine responses were greater in fat ewes than lean ewes but norepinephrine responses were similar. Our results suggest that relative levels of adipose tissue influence the stress-induced activity of the hypothalamopituitary-adrenal axis and some aspects of the sympathoadrenal system with fat animals having higher responses than lean animals.

Central infusion of leptin does not increase AMPK signaling in skeletal muscle of sheep

“…Plasma glycerol concentration was determined using an enzymatic fluorometric technique (7) on a 96-well plate. Plasma concentrations of growth hormone and cortisol were measured by radioimmunoassay, as previously described (25,64), and pulse analysis of growth hormone concentrations was undertaken using PULSAR analysis (25).…”

Stressor Specificity of Sex Differences in Hypothalamo-Pituitary-Adrenal Axis Activity: Cortisol Responses to Exercise, Endotoxin, Wetting, and Isolation/Restraint Stress in Gonadectomized Male and Female Sheep

“…Our experience is that 1 d is sufficient for animals to adjust from being outdoors on pasture to being penned indoors as in previous studies (4,7,13,15,20). Animals were weighed before the commencement of the studies.…”

“…For example, cortisol responses to stress can be influenced by the sex of an individual (4 -6), the amount of visceral adipose tissue an individual is carrying (7), and whether an individual is lactating (8). There also appear to be individuals who are naturally more or less responsive to stress, possibly due to factors such as genetic predisposition, early life experience, and/or environmental effects (3).…”

Refining a ‘toolkit’ for objective assessment of pain and stress in ruminants

“…A similar finding was also observed in another surgical castration study in cattle, in which the elevation in cortisol concentrations did not differ from the control animals, which were only handled (Coetzee et al, 2008). Increases in cortisol are also associated with psychological stressors such as weaning (Kim et al, 2011), isolation (Rivalland et al, 2007;Tilbrook et al, 2008) and transportation (Qiu et al, 2007;Kostro et al, 2009;Giannetto et al, 2011). It has been suggested by Stafford and Mellor (2005) that isolation and restraint are emotionally noxious experiences to the animals.…”