Epinephrine (EPI) and Norepinephrine (NE) What are the sources of EPI and NE? – EPI and NE are produced in cells in the adrenal medulla, but EPI is more prevalent from this source. Sympathetic neurons activate the adrenal medulla. Both EPI and NE are secreted into blood during activation, and will act as hormones binding to adrenergic receptors in targets. – NE is released directly on target cells by efferent fibers of sympathetic neurons. Here NE is acting as a neurotransmitter that binds to adrenergic receptors. – There are major NE neurons in the brain that play a role in the integration of sleep-wake cycles and responses to stress.

Epinephrine (EPI) and Norepinephrine (NE) What will stimulate their secretion from sources? – Many stimuli can activate sympathetic neural pathways, but they are generally associated with stress and the “flight or fight” response where the organism is trying to generate a coordinated response to a perceived or actual threat. – They are also activated under milder forms of stress like exercise, in which the organism is also generating a coordinated and energetic physiological response. – Hypoglycemic conditions will also increase NE/EPI levels.

Epinephrine (EPI) and Norepinephrine (NE) What are the actions of EPI/NE on the various targets with adrenergic receptors? – Cardiovascular: increase blood pressure via increased heart rate and vasoconstriction in most arterioles – Lungs: open airways via bronchodilation to increase airflow – Play role in cooling body during thermoregulation Sweat glands: increase activity Cutaneous arterioles: lead to vasodilation and increase flow to skin – GI tract: in general NE and EPI inhibit activity – Will lead to higher levels of fuel in plasma Adipocytes: lipolysis that leads to higher fatty acids in blood Liver: increase glycogenolysis and higher plasma glucose Pancreas: inhibits beta cells (lowers insulin) and activates alpha cells (elevated glucagon)– leads to higher plasma glucose

Epinephrine (EPI) and Norepinephrine (NE) What are the endocrine connections? – Direct effects listed above that occur during sympathetic activation of adrenal medulla during a stress response – Thyroid hormone is permissive on the actions of EPI/NE by increasing # of adrenergic receptors in targets, increasing the effect of circulating EPI/NE. – Cortisol will increase levels of EPI synthesis in cells of the adrenal medulla, thus increasing the above responses. Cortisol also has a permissive effect on the smooth muscles around blood vessels that respond to circulating levels of EPI/NE, increasing vasoconstriction and thus blood pressure.

Stress that affects EPI/NE pathways Increases of NE from sympathetic neurons. Increases of EPI/NE in plasma from adrenal medulla. Increases of NE from sympathetic neurons. Increases of EPI/NE in plasma from adrenal medulla. Maintain high plasma oxygen. Increase fuels in plasma. Increase in blood flow for delivery of fuel and oxygen. Increase removal of thermal energy gains. Maintain high plasma oxygen. Increase fuels in plasma. Increase in blood flow for delivery of fuel and oxygen. Increase removal of thermal energy gains.