Epinephrine (EPI) and Norepinephrine (NE)

1
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.

2
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.

3
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

4
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.

5
Stress that affects EPI/NE pathways
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.