Brief Summary of Effects of Catecholamines on Tissues and Organs of the Body
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Tissue/Organ Catecholamine Effect
Heart Increases rate Increases speed of impulse conduction Increases contractility
Respiratory tract Relaxes bronchial smooth muscle to dilate airway
Vascular smooth muscle Skin, mesenteric bed, kidneys
Constricts to reduce perfusion
Skeletal muscle, lungs, heart Dilates to increase perfusion Peripheral vasculature Constricts to increase blood pressure Gastrointestinal tract Decreases peristalsis
Contracts sphincters Decreases gastric acid secretion
Eyes Contracts radial muscle to dilate iris and pupil
Relaxes ciliary muscle for far vision Liver Glycogenolysis and gluconeogenesis
for increased glucose levels and thus energy
Central nervous system Promotes arousal, attention, and vigilance
TABLE 2.3 Major Effects of Glucocorticoids in the Stress Response Metabolism Catabolism of muscle, fat, lymphoid tissue,
skin, and bone Liver gluconeogenesis Opposes insulin in transport of glucose
into cells Increased appetite
Fluid balance Sodium and water retention Inflammation and infection Suppressed inflammatory response
Increased neutrophil release Decreased new antibody release Decreased T-lymphocyte production and
function Decreased production of eosinophils,
basophils, and monocytes Support catecholamines Increased epinephrine synthesis
Enhanced vasoconstriction
CHAPTER 2 Homeostasis, Allostasis, and Adaptive Responses to Stressors 19
interacts with numerous neurotransmitters in the brain, counteracting the depressive tendencies often noted with glucocorticoids. Testosterone also appears to have antidepressant and antianxiety effects as it elevates mood. Numerous stressful stimuli, such as illness, surgery, strenuous physical exercise, heart failure, and stressful academic programs, result in significant reductions in circulating testosterone levels. In combination with another hormone, vasopressin, testosterone enhances blood pressure and heart rate reactivity and augments the “fight-or-flight” response. In contrast, the hormone oxytocin (whose impact is modulated by estrogen) and the endogenous opioids are thought to produce a calming effect during times of stress, resulting in the notion that women may have a “tend and befriend” response rather than a “fight-or-flight” response in some situations.
Growth Hormone, Prolactin, and Oxytocin Growth hormone (somatotropin) is released from the anterior pituitary gland and affects protein, lipid, and carbohydrate metabolism. It has anabolic effects, increasing protein synthesis and bone and muscle mass growth. It also increases fat mobilization (lipolysis) while decreasing the rate of carbohydrate utilization by peripheral tissues. Growth hormone is normally secreted in a cyclic basal pattern, primarily at night, and changes with developmental stage. Growth hormone secretion is highest during adolescence and then gradually declines during adult- hood. Serum levels of growth hormone also increase acutely after a variety of intensely stressful physical or psychological stimuli, such as strenuous exercise or extreme fear. Growth hormone appears to enhance immune function. However, continued activation of the stress response eventually results in the decreased secretion of growth hormone, accounting for stunted growth in children experiencing prolonged chronic stress.
Prolactin is similar in structure to growth hormone and is secreted from the anterior pituitary gland in response to stress, sexual activity, pregnancy, and suckling (even in men) and breast feeding. It suppresses ovulation. Numerous tissues have receptors for prolactin in addition to the breast, including the kidneys, liver, and adrenal glands. Lym- phocytes also have prolactin receptors, suggesting a role for prolactin in immune regulation. A significant increase in the level of growth hormone or prolactin tends to require more intense stimuli than the stress that increases the concentrations of catecholamines and glucocorticoids.
Oxytocin is produced during childbirth, lactation, and sexual behavior (in both genders) and has been associated with promoting bonding and social attachment. Oxytocin is thought to moderate the stress response and have a calming effect, with reductions in HPA and sympathetic activation and reduced perceived anxiety. In an intriguing study, researchers found that preteenage girls who spoke with their mothers on the phone immediately after a laboratory social stressor had higher levels of urinary oxytocin and lower levels of salivary cortisol than did those who merely texted their mothers. Hearing the mother’s voice appeared important to the release of the oxytocin and buffered the stress response. Oxytocin also may have some analgesic effects. It is synthesized by the hypothalamus and secreted by the posterior pituitary gland and other brain regions. Oxytocin is believed to have stronger effects in females in comparison to males because of the interaction of estrogen and oxytocin.
Through interactions of the primary stress hormones—catecholamines and glucocorticoids—as well as numerous other mediating influences, the allostatic process needed to sustain the human organism is achieved. In some cases, these stress-related hormones have similar and synergistic effects and in others they work in opposition. This state of counterbalanc- ing helps to facilitate allostasis, ideally returning the human organism back toward homeostasis.
a small amount of mineralocorticoid effect, but the greatest effect on circulating volume is through aldosterone. Additionally, angiotensin II, whose formation stimulates aldosterone release, is a potent vasoconstric- tor. This chemical mediator provides support for the catecholamine- induced increase in blood pressure.