Epinephrine

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Epinephrine is also known as adrenaline. It is a steroid hormone which is released by chromaffin cells in the adrenal glands as part of the 'fight or flight' response. Epinephrine is an amino acid derivative of tyrosine secreted from the adrenal medulla. The polarity of the epinephrine molecule allows it to bind to a stimulatory G protein which is coupled to Beta-adrenergenic receptors on the surface of the liver[1]. Initially, the G protein is inactive with guanosine diphosphate (GDP) bound. Once epinephrine binds the GDP molecule is released and guanosine triphosphate (GTP) is attached, activating the G protein. The alpha subunit of the G protein binds to and activates adenylyl cyclase catalysing the conversion of ATP to cAMP. cAMP converts phosphorylase α into phosphorylase β, activating protein kinase A (PKA)[2]. PKA goes on to phosphorylate other target proteins making glycogen synthase less active by phosphorylation using a phosphate from ATP resulting in less glycogen being synthesised[3]. PKA also adds a phosphate to phosphorylase kinase[4]. This activates glycogen phosphorylase, increasing breakdown of glycogen into glucose releasing lots of energy rapidly. One epinephrine-binding molecule can cause activation of hundreds of phosphorylations through amplification of the cell signalling cascade and can produce a permanent change in enzyme molecules. This response can be induced by stress or other stimuli in the environment and causes many physiological effects such as increased heart rate, increased blood sugar levels (due to the conversion of glycogen to glucose in the liver); increased breathing rate, constriction of peripheral blood vessels and dilation of the pupils[5][6].

Epinephrine injections can cause side effects such as :

Reference

  1. Lodish H, Berk A, Zipursky S, Mastudaira P, Balitmore D, Darnell J, Molecular Cell Biology, Section 20.3, 4th edition, W.H. Freeman, 2000
  2. Citric cycle, Krantz B, Principles of Biochemistry, “Principles of Metabolic Regulation” Chapter 15, Berkeley, 2008
  3. Diwan J, Glycogen Metabolism, 2007 https://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/glycogen.htm, cited on 12/11/2016
  4. Diwan J, Glycogen Metabolism, 2007 https://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/glycogen.htm, cited on 12/11/2016
  5. Alberts et al. (2008:G2), Molecular Biology of the Cell, 5th edition, New York: Garland Science
  6. The American Society of Health-System Pharmacists (2015). https://www.nlm.nih.gov/medlineplus/druginfo/meds/a603002.html date visited 20/10/2015
  7. American Society of Health-System Pharmacists (2012). https://www.nlm.nih.gov/medlineplus/druginfo/meds/a603002.html
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