Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: September 3, 2004
Publication Date: N/A
Technical Abstract: Stress hormones are those hormones whose concentrations are considered to be altered, either increased or decreased, when an animal is exposed to a stressor. An animal's physiologic response to stress concentrates on meeting its needs for the 'flight or fight' response. Toward this end, hormones are altered in order to: 1) change blood flow so that blood is directed toward those tissues such as skeletal and cardiac muscle and away from 'non-essential' tissues such as the gastrointestinal tract; 2) increase energy by creating and liberating glucose, and 3) cause lypolysis to liberate free fatty acids from fat as an energy source to be used in the response. Thus, the main stress hormones have been considered to be glucocorticosteroids (predominantly cortisol and corticosterone), epinephrine (a neurohormone), and norepinephrine (a neurotransmitter). The challenge in defining a single or class of 'stress hormones' is that the hormones and neurotransmitters currently used are all non-specific to the stress response. Each of those listed have base functions in the body to maintain homeostasis, and thus are present and measurable even when an animal is not stressed. The reason they have been commonly referred to as stress hormones is because when an animal is challenged with aversive stimuli these hormones and neurotransmitters are increased. However, these same compounds are increased when animals experience states not considered to be stressful, such as exercise and copulation. Along with these traditional hormones listed above, stress research has also measured a variety of other hormones when assessing stress in animals. Traditional stress hormones cause a wide variety of effects in the body and thus they also alter many other hormones and compounds which have been used to assess stress in animals. For instance, it is well known that glucocorticosteroids inhibit luteinizing hormone (LH) which has allowed researchers to use LH as a measure of stress in animals. Similarly, glucocorticosteroids also inhibit insulin like growth factor- 1 (IGF-1) which has allowed its successful use in measuring stress as well. If a single stress hormone exists and can be identified, the research field of animal welfare and stress physiology will be greatly enhanced.