noradrenaline

Examples of noradrenaline in the following topics:

• Adrenal Medulla

  • The adrenal medulla secretes approximately 20% noradrenaline (norepinephrine) and 80% adrenaline (epinephrine).
  • When stimulated, chromaffin cells secrete adrenaline and noradrenaline along with enkephalin and enkephalin-containing peptides into the bloodstream.
  • The secreted adrenaline and noradrenaline play an important role in the fight-or-flight response.

• Adrenergic Neurons and Receptors

  • The adrenergic receptors (or adrenoceptors) are a class of metabotropic G protein-coupled receptors that are targets of the catecholamines, especially norepinephrine or noradrenaline, and epinephrine (adrenaline).
  • Adrenaline or noradrenaline are receptor ligands to α1, α2, or β-adrenergic receptors (the pathway is shown in the following diagram).
  • Negative feedback in the neuronal synapses—presynaptic inhibition of noradrenalin release in CNS.
  • Adrenaline and noradrenaline are ligands to α1, α2, or β-adrenergic receptors. α1-receptors couple to Gq, resulting in increased intracellular Ca2+ and causing smooth muscle contraction. α2 receptors couple to Gi, causing a decrease in cAMP activity and resulting in smooth muscle contraction. β-receptors couple to Gs, increasing intracellular cAMP activity and resulting in heart muscle contraction, smooth muscle relaxation, and glycogenolysis.

• Stress and Disease

  • In depression, the transmission of noradrenaline is reduced from both of the principal noradrenergic centres.
  • An increase in noradrenaline in the frontal/prefrontal cortex modulates the action of selective noradrenaline re-uptake inhibition and improves mood.
  • Increasing noradrenaline transmission to other areas of the frontal cortex modulates attention.

• The Fight-or-Flight Response

  • The fight-or-flight response is regulated by the release of adrenaline or noradrenaline.
  • Simultaneously, the adrenal gland also releases catecholamine hormones, such as adrenaline or noradrenaline, into the blood stream.

• Sympathetic Nervous System

  • This secretion activates the secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine) from the adrenal medulla.

• Sympathetic Responses

  • This occurs as the preganglionic sympathetic fibers that end in the adrenal medulla secrete acetylcholine, which activates the secretion of adrenaline (epinephrine), and to a lesser extent noradrenaline (norepinephrine).
  • Catecholamine hormones, such as adrenaline or noradrenaline, facilitate the immediate physical reactions associated with a preparation for violent muscular action.

• The Stress Response

  • This response is also referred to as the sympatho-adrenal response of the body owing to the fact that the preganglionic sympathetic fibers that end in the adrenal medulla secrete acetylcholine, which activates the release of adrenaline and noradrenaline from the medulla.

• Agonists, Antagonists, and Drugs

  • Beta blockers block the action of endogenous catecholamines—epinephrine (adrenaline) and norepinephrine (noradrenaline) in particular—on β-adrenergic receptors, part of the sympathetic nervous system that mediates the fight-or-flight response.