epinephrine

Examples of epinephrine in the following topics:

• Epinephrine and Norepinephrine

  • As a hormone and neurotransmitter, epinephrine acts on nearly all body tissues.
  • Epinephrine acts by binding to a variety of adrenergic receptors.
  • Epinephrine is a nonselective agonist of all adrenergic receptors, including the major subtypes α1, α2, β1, β2, and β3.
  • Epinephrine and norepinephrine are released by the adrenal medulla and nervous system respectively.
  • Kidney function is halted temporarily by epinephrine and norepinephrine.

• 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, as seen in , and epinephrine (adrenaline) as shown in ).
  • Adrenaline (epinephrine) reacts with both α and βadrenoreceptors, causing vasoconstriction and vasodilation, respectively.
  • Although α receptors are less sensitive to epinephrine, when activated, they override the vasodilation mediated by βadrenoreceptors.
  • The result is that high levels of circulating epinephrine cause vasoconstriction.
  • At lower levels of circulating epinephrine, βadrenoreceptor stimulation dominates, producing an overall vasodilation.

• Overview of the Adrenal Glands

  • They are chiefly responsible for releasing hormones in response to stress through the synthesis of corticosteroids such as cortisol and catecholamines such as epinephrine.
  • The cortex mainly produces cortisol, aldosterone and androgens, while the medulla chiefly produces epinephrine and norepinephrine.
  • It secretes approximately 20% norepinephrine and 80% epinephrine.
  • Cortisol also promotes epinephrine synthesis in the medulla.

• Hormonal Regulation of Stress

  • The hormones epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline) are released by the adrenal medulla.
  • Epinephrine and norepinephrine increase blood glucose levels by stimulating the liver and skeletal muscles to break down glycogen and by stimulating glucose release by liver cells.
  • Epinephrine and norepinephrine are collectively called catecholamines.
  • The body cannot sustain the bursts of energy mediated by epinephrine and norepinephrine for long times.
  • When an animal feels threatened, epinephrine and norepinephrine released by the adrenal medulla prepare the body to fight a threat or flee from it by breaking down stores of glycogen, which provides an immediate boost of energy.

• Lipid-Derived, Amino Acid-Derived, and Peptide Hormones

  • For example, cortisol has a half-life of 60 to 90 minutes, whereas epinephrine, an amino acid derived-hormone, has a half-life of approximately one minute.
  • Examples of amino acid-derived hormones include epinephrine and norepinephrine, which are synthesized in the medulla of the adrenal glands, and thyroxine, which is produced by the thyroid gland.
  • (a) The hormone epinephrine, which triggers the fight-or-flight response, is derived from the amino acid tyrosine.

• Humoral, Hormonal, and Neural Stimuli

  • Recall that in a short-term stress response, the hormones epinephrine and norepinephrine are important for providing the bursts of energy required for the body to respond.
  • Here, neuronal signaling from the sympathetic nervous system directly stimulates the adrenal medulla to release the hormones epinephrine and norepinephrine in response to stress.

• Adrenal Glands

  • The adrenal medulla contains two types of secretory cells: one that produces epinephrine (adrenaline) and another that produces norepinephrine (noradrenaline).
  • Epinephrine is the primary adrenal medulla hormone, accounting for 75 to 80 percent of its secretions.
  • Epinephrine and norepinephrine increase heart rate, breathing rate, cardiac muscle contractions, blood pressure, and blood glucose levels.
  • The release of epinephrine and norepinephrine is stimulated by neural impulses from the sympathetic nervous system.

• Adrenal Medulla

  • The adrenal medulla secretes approximately 20% norepinephrine and 80% epinephrine.
  • Cortisol also promotes epinephrine synthesis in the medulla.
  • Chromaffin cells of the adrenal medulla are innervated by the splanchnic nerve; they secrete adrenaline (epinephrine), noradrenaline (norepinephrine), enkephalin and enkephalin-containing peptides into the blood stream.
  • A pheochromocytoma or phaeochromocytoma (PCC) is a neuroendocrine tumor of the medulla of the adrenal glands (originating in the chromaffin cells), or extra-adrenal chromaffin tissue that failed to involute after birth and secretes high amounts of catecholamines—usually noradrenaline (norepinephrine) and, to a lesser extent, adrenaline (epinephrine).

• Interactions of Hormones at Target Cells

  • For example, thyroid hormone increases the number of receptors available for epinephrine at the latter's target cell, thereby increasing epinephrine's effect at that cell.
  • Without the thyroid hormone, epinephrine would have only a weak effect.

• Role of the Cardiovascular Center

  • Hormones such as epinephrine and norepinephrine or changes in pH such as an acidification due to carbon dioxide accumulation in a tissue during exercise are detected by chemoreceptors.