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

Abstract

Sex differences in the stress-induced activity of the hypothalamo-pituitary-adrenal axis in sheep appear to be dependent on the stressor encountered and occur irrespective of the presence of gonadal steroids. We tested the hypotheses that cortisol responses to exercise, endotoxin, wetting (experiment 1), and isolation/restraint (experiment 2) stress differ between gonadectomized male and female sheep. At weekly intervals (in experiment 1), we subjected gonadectomized rams and ewes (n ϭ 6/group) to control conditions, to exercise stress, to iv injection of endotoxin, and to wetting stress. In a second experiment (experiment 2), we subjected gonadectomized rams and ewes (n ϭ 5/group) to control conditions or to isolation/restraint stress. In both experiments, we measured plasma concentrations of cortisol before, during, and after stress at a frequency of at least 15 min with samples collected (from an indwelling jugular catheter) at a greater frequency around the time of the stressor. Cortisol responses to wetting (experiment 1) and isolation/restraint (experiment 2) stress were significantly higher in females compared with males but in response to exercise (experiment 1) and endotoxin (experiment 1) stress, there were no differences between the sexes. For some stressors, there are sex differences in sheep in the stress-induced activity of the hypothalamo-pituitary-adrenal axis that are independent of the presence of the sex steroids, but the existence of these sex differences and the direction of these sex differences differs, depending on the stressor imposed. (Endocrinology 151: 4324 -4331, 2010) S ustained or repeated stress can lead to a range of chronic disease states such as obesity, metabolic syndrome, hypertension, autoimmunity, allergy, insomnia, depression, pain syndromes, and fatigue syndromes (1). Stress can be defined as a complex physiological state that embodies a range of integrative physiological and behavioral processes that occur when there is a real or perceived threat to homeostasis (2). A common response to stress is the activation of the hypothalamopituitary-adrenal axis, which results in the sequential secretion of CRH and arginine vasopressin from the hypothalamus, ACTH from the anterior pituitary, and glucocorticoids such as cortisol from the adrenal cortex. Together with other pathways, activation of the hypothalamo-pituitary-adrenal axis returns the organism to a state of homeostasis, but pathologies can develop when the activation of these pathways is severe and/or prolonged. Cortisol is thought to be responsible for many of the longer term effects of stress.There is an increasing amount of evidence to show that different physiological characteristics of an individual can influence cortisol responses to stress (3). 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 les...

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Stocking Density Affects Stress and Anxious Behavior in the Laying Hen Chick During Rearing

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Adipose and skeletal muscle thermogenesis: studies from large animals

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