Difference Between Norepinephrine and Epinephrine
Main Difference – Norepinephrine vs Epinephrine
Norepinephrine and epinephrine are two similar chemical messengers which act as hormones. They are released by adrenal medulla. Both of them are catecholamines, which are derived from the amino acid, tyrosine. Norepinephrine and epinephrine are involved in the regulation of stress responses, arterial blood pressure, and metabolism. They also bear similar chemical structures with the exception of epinephrine’s methyl group. The main difference between norepinephrine and epinephrine is that norepinephrine raises the heart rate and modulate bold pressure whereas epinephrine is an effective antihistamine, which is used in the treatment of shock.
Key Areas Covered
1. What is Norepinephrine
– Definition, Characteristics, Function
2. What is Epinephrine
– Definition, Characteristics, Function
3. What is the difference between Norepinephrine and Epinephrine
– Comparison of Key Differences
Key Terms: Adrenaline, Epinephrine, Noradrenaline, Norepinephrine 
What is Norepinephrine
Norepinephrine or noradrenaline is a chemical substance, which is released from the sympathetic nervous system and adrenal medulla in response to stress. It is a neurotransmitter which can also act as a stress hormone. Norepinephrine is produced in the shafts of the nerves in the sympathetic nervous system and is stored in vesicles. It is released into the synapse when an action potential travels down the presynaptic neuron. Then, it binds with the receptors in the postsynaptic neuron. The sympathetic nervous system prepares the body for a ‘fight or flight response’. Adrenal medulla-made norepinephrine is released into the blood as a hormone. Norepinephrine causes vasoconstriction, which is important to maintain blood pressure. It triggers the following responses;
Figure 1: Norepinephrine
Carbon: black, Hydrogen: white, Nitrogen: blue, Oxygen: red
What is Epinephrine
Epinephrine or adrenaline is a hormone secreted by the medulla of adrenal glands. It is produced during strong emotions like fear or anger, giving a surge of energy to the body and released into the blood stream in order to act on almost all the body tissues. Epinephrine is capable of constricting blood vessels in order to maintain blood pressure. It relaxes breathing tubes, allowing easier breathing as well. Eventually, epinephrine increases the heart rate, blood pressure, and sugar metabolism and muscle strength. Epinephrine stimulates alpha and beta receptors, but it is more effective on alpha receptors, which are involved in insulin secretion in the pancreas, glycogen breakdown in liver and muscle, and glycolysis. Beta receptors are involved in the glucagon secretion in the pancreas, increased ACTH secretion by the pituitary gland, and increased fat metabolism in adipose tissue.
Due to its tendency of constricting blood vessels as well as the opening of airways, epinephrine is used in medicine to maximize blood flow to the heart during a cardiac arrest. It is also administrated in anaphylactic shock to jump-start the heart. In anaphylactic shock, the heart stops pumping blood due to allergic reactions. Epinephrine is also an immediate treatment for asthma shocks.
Figure 2: Epinephrine
Carbon: black, Hydrogen: white, Nitrogen: blue, Oxygen: red
Difference Between Norepinephrine and Epinephrine
Definition
Norepinephrine: Norepinephrine is a hormone which serves as a neurotransmitter.
Epinephrine: Epinephrine is a hormone that increases rates of blood circulation, breathing, and carbohydrate metabolism.
Alternative Names
Norepinephrine: Norepinephrine is also called noradrenaline.
Epinephrine: Epinephrine is also called adrenaline.
Production
Norepinephrine: Norepinephrine is produced in adrenal medulla and sympathetic nerves.
Epinephrine: Epinephrine is exclusively produced in the adrenal medulla.
Significance
Norepinephrine: Norepinephrine is used as a drug to raise blood pressure.
Epinephrine: Epinephrine prepares muscles for exertion.
Chemical Structure
Norepinephrine: Norepinephrine is a catecholamine.
Epinephrine: Epinephrine is structurally similar to norepinephrine, except for the methyl group present in it.
In Adrenal-medullary Output
Norepinephrine: Norepinephrine takes 80% of the adrenal-medullary output.
Epinephrine: Epinephrine takes only 20% of the adrenal-medullary output.
Mediation of the Effect of the Hormone
Norepinephrine: The effect of the norepinephrine is mediated by the sympathetic nervous system.
Epinephrine: The effect of epinephrine is mediated by adrenal medulla.
Affinity for Adrenergic Receptors
Norepinephrine: Norepinephrine binds with alpaha-1, alpha-2, and beta-1 receptors located near postganglionic sympathetic-fiber terminals.
Epinephrine: Epinephrine binds with alpha receptor in greater affinity.
Function
Norepinephrine: Norepinephrine raises the heart rate and modulates bold pressure.
Epinephrine: Epinephrine is an effective antihistamine, which is used in the treatment for shock.
Conclusion
Norepinephrine and epinephrine are two similar types of neurotransmitters, which play an essential role in stress response. Both neurotransmitters are involved in the vasoconstriction and relaxing breathing tubes, allowing the maintenance of blood pressure. Norepinephrine is synthesized in sympathetic neurons and epinephrine is synthesized in adrenal medulla. Norepinephrine is used as a drug to raise blood pressure and epinephrine prepares the muscle for exertion. The main difference between norepinephrine and epinephrine is in their uses in medicine.
Reference:
1. “What Is Norepinephrine? – Effects, Function & Definition.” Study.com. N.p., n.d. Web. Article here. [Accessed 30 May 2017].
2. “What Is Epinephrine? – Definition, Uses & Side Effects.” Study.com. N.p., n.d. Web. Article here. 30 May 2017.
3. “Norepinephrine vs Epinephrine: What’s the difference?” Drugs.com. N.p., n.d. Web. Article here. 30 May 2017.
Image Courtesy:
1.”Norepinephrine ball-and-stick model” By Vaccinationist – PubChem (CC BY-SA 4.0) via Commons Wikimedia
2. “Epinephrine ball-and-stick model” By Vaccinationist – PubChem (CC BY-SA 4.0) via Commons Wikimedia
ncG1vNJzZmiolZm2oq2NnKamZ5Ses6ex0Z6lnJ1dl7K1w8SepWamn6eysbXNnqehqpmjsm6tzZ1knqiZo7KxtNGipZ5n