Disclaimer Show
Oxford University Press makes no representation, express or implied, that the drug dosages in this book are correct. Readers must therefore always … More Oxford University Press makes no representation, express or implied, that the drug dosages in this book are correct. Readers must therefore always check the product information and clinical procedures with the most up to date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulations. The authors and the publishers do not accept responsibility or legal liability for any errors in the text or for the misuse or misapplication of material in this work. Except where otherwise stated, drug dosages and recommendations are for the non-pregnant adult who is not breastfeeding. You do not currently have access to this chapter. IntroductionAdrenaline (Epinephrine), Noradrenaline (Norepinephrine) and Dopamine are amongst a group called catecholamine, which functions as neurotransmitters and hormones within the human body. These three compounds are naturally occurring and are produced in the body. Isoprenaline, unlike the others, is a synthetic catecholamine and is not naturally present in the body. It has an essential pharmacological significance and hence should be mentioned. As the name suggests, it is a catechol group (a benzene ring with two hydroxyl groups) which is attached to an amine group (nitrogen-containing group) as seen in figure 1 from the Rang & Dale’s Pharmacology. Catecholamine’s key role at rest is thermogenesis (generation of body heat) and nutrient metabolism. Certain catecholamines during a stressful event will favour the body to either defend itself at its full potential or run away from danger. This is known as fight/flight, an evolutionary adaption to survival. These neurotransmitters and hormones stimulate oxygen usage and the consumption of fuels by using free fatty acids and glucose, which causes body heat generation. They also play a role in stimulating glycogenolysis and using the stored fat to break it down to free fatty acids through a process called lipolysis. Catecholamines can regulate the secretion of certain hormones in the body. This has been demonstrated by Dopamine inhibiting Prolactin secretion, Adrenaline which inhibits Insulin secretion and finally Noradrenaline which stimulates the release of Gonadotropin-releasing hormone (GnRH). Synthesis of catecholaminesFigure 1. Biosynthesis of the catecholamines. From: Rang & Dale’s Pharmacology, 7th edition. The beginning of the synthesis of catecholamines all starts with an amino acid, L-tyrosine. The biosynthesis sequence goes as follow: Tyrosine -> DOPA (dihydroxyphenylalanine) -> Dopamine -> Noradrenaline (Norepinephrine) -> Adrenaline (Epinephrine). As seen in figure 1, the tyrosine hydroxylase introduces a hydroxyl group (-OH) into an organic compound. This is a rate-limiting step. The decarboxylase enzyme is responsible for removing a carboxyl group in an organic compound; in this case, the carboxylic acid is removed. The Dopamine beta-hydroxylase will add a hydroxyl group (-OH) on the beta carbon making the compound into Noradrenaline. The finals step is about adding a methyl group from another compound to the amine group on the Noradrenaline. This process is done by taking a methyl group from the two amino acid compound S-Adenosyl-L-methionine (AdoMet) and transferring it to the Noradrenaline, making Adrenaline as a final product. Where are catecholamines synthesised? There are three central locations that synthesise catecholamine. These are the brain, the adrenal medulla and certain sympathetic nerve fibres. Interestingly, the nerve synthesising catecholamines is dependent on the enzyme present that is part of the biosynthesis. This is seen in dopaminergic neurons, where they only have the first two enzymes (tyrosine hydroxylase and DOPA decarboxylase). Hence, when a dopaminergic neuron gets stimulated, there is a release of Dopamine at the synapse. In terms of the transformation of Noradrenaline to Adrenaline at the adrenal medulla, the enzyme needs to be in the presence of a high local concentration of glucocorticoids from the adrenal cortex. If the chromatin cells (the primary source of circulating catecholamines) are outside the adrenal medulla, they are unable to synthesise Adrenaline. Differences and similaritiesDifferencesAdrenaline
*it is seen that a small amount of Adrenaline is released from the end of the sympathetic neurons and act as a neurotransmitter at the synapse. Noradrenaline
Similarities
Bottom lineNoradrenaline: Increase or maintain blood pressure during an acute medical situation. Used for vasodilatory shock states. Mainly produced in the neurons and act as a neurotransmitter. A small amount is made in the adrenal medulla and acts as a hormone. Adrenaline: Four main actions: increase heart rate and force of contractility, bronchodilation, increase vasoconstriction hence increase blood pressure and finally increase blood glucose availability. Used for anaphylactic shock, emergency asthma attacks, septic shock, cardiac arrest, eye surgery and local anaesthesia. Mainly produced in the adrenal medulla and act as a hormone; hence, has a wide range effect on the body. A small amount is made in the nerves and acts as a neurotransmitter. Both are released for a fight and flight response for survival adaptation. Published 20th January 2020. Last reviewed 1st December 2021. ReferenceDrugbank Authors. Epinephrine. Drugbank website. https://www.drugbank.ca/drugs/DB00668. Updated January 16, 2020. Accessed January 18, 2020. Drugbank Authors. Norepinephrine. Drugbank website. https://www.drugbank.ca/drugs/DB00368. Updated January 16, 2020. Accessed January 18, 2020. Drugs.com Authors. Norepinephrine vs epinephrine: what's the difference? Drugs.com website. https://www.drugs.com/medical-answers/norepinephrine-epinephrine-difference-3132946/. Updated September 13, 2018. Accessed January 18, 2020. Kara Rogers. Catecholamine. Encyclopaedia Britannica website. https://www.britannica.com/science/catecholamine. Updated and revised August 5, 2015. Accessed January 17, 2020. Kara Rogers. Epinephrine. Encyclopaedia Britannica website. https://www.britannica.com/science/epinephrine. Updated and revised December 21, 2009. Accessed January 18, 2020. Kara Rogers. Norepinephrine. Encyclopaedia Britannica website. https://www.britannica.com/science/norepinephrine. Updated and revised December 21, 2009. Accessed January 18, 2020. Lakna. What is the Difference Between Adrenaline and Noradrenaline. Encyclopaedia Britannica website. PEDIAA website. https://pediaa.com/what-is-the-difference-between-adrenaline-and-noradrenaline/. Revised December 20, 2018. Accessed January 18, 2020. Ritter J, Flower R, Henderson G, Loke YK, MacEwan D, Rang H. Rang & Dale's Pharmacology. 7th ed. London: Elsevier; 2019. eBook ISBN: 9780702074462. USEFUL WEBSITES AND LINKS:
Which of the following is a similarity between dopamine and acetylcholine?Which of the following is a similarity between the neurotransmitters dopamine and acetylcholine? Both are involved in the learning process.
What are the 3 main neurotransmitters?These neurotransmitters are involved in most functions of your nervous system.. Glutamate. This is the most common excitatory neurotransmitter of your nervous system. ... . Gamma-aminobutryic acid (GABA). GABA is the most common inhibitory neurotransmitter of your nervous system, particularly in your brain. ... . Glycine.. Which of the following is a similarity between the central nervous system?Which of the following is a similarity between the central nervous system and the peripheral nervous system? Their structures are composed of neurons and neuroglia.
What are the 4 types of neurotransmitters?Neurotransmitters all serve a different purpose in the brain and body. Although there are several different minor and major neurotransmitters, we will focus on these major six: acetylcholine, dopamine, norepinephrine, serotonin, GABA, and glutamate.
|