Norepinephrine vs. Epinephrine: What’s the Difference?

Epinephrine is also called adrenaline, and norepinephrine is also known as noradrenaline. Both are natural bodily chemicals made by the adrenal glands. The adrenal glands are triangular-shaped glands located above the kidneys and composed of two parts: the cortex and the medulla. 

The adrenal glands produce other hormones in addition to epinephrine and norepinephrine including cortisol, aldosterone, and dehydroepiandrosterone (DHEA). These hormones regulate metabolism, immune system function, stress response, blood pressure, and more. The pituitary gland in the brain controls the production of these adrenal hormones.

What is the Role of Adrenaline and Noradrenaline?

Adrenaline and noradrenaline (or epinephrine and norepinephrine) belong to a group of naturally occurring compounds in the human body called catecholamines. They function both as hormones and neurotransmitters (chemical signals). The parts of the body that use epinephrine and norepinephrine are called the adrenergic and noradrenergic body systems.

Hormones and neurotransmitters are chemical messengers in the body. Hormones are secreted into the bloodstream by certain endocrine glands to carry messages to the body’s tissues and organs. Neurotransmitters are released into the spaces between nerve cells to allow nerve cells to communicate with each other. After neurotransmitters carry out their function, nerve cells reabsorb them (this is known as reuptake). 

Catecholamines like epinephrine and norepinephrine interact with adrenergic receptors or adrenoceptors, which are proteins on the cell surfaces, to produce responses in the target cells. There are different types of adrenergic receptors in different parts of the body, such as alpha 1, alpha 2, beta 1, beta 2, and beta 3 adrenoceptors.

What is the Main Difference Between Epinephrine and Norepinephrine?

The key differences between norepinephrine vs. epinephrine are as follows:

Other Names

• Norepinephrine is also called noradrenaline.

• Epinephrine is also called adrenaline. 

Receptors Activated

• Norepinephrine primarily binds to alpha receptors located in blood vessels. 

• Epinephrine has a more significant effect on beta receptors found in the heart, lungs, and skeletal muscles. 

Effects on the Body

• Norepinephrine narrows blood vessels and increases heart rate and blood pressure. Norepinephrine is always available in the blood in small, steady amounts to maintain blood pressure.

• Epinephrine narrows blood vessels and acts as a vasopressor (increases blood pressure). It also dilates (relaxes or widens) air passages.

Norepinephrine Overview

What Is The Main Function of Norepinephrine?

The main function of norepinephrine is to raise blood pressure. The adrenal medulla produces the hormone norepinephrine in response to low blood pressure. Norepinephrine activates mostly alpha receptors present in arteries. While it does exert effects on beta receptors, this effect is less significant. 

Effect on Blood Vessels: Is Norepinephrine a Vasodilator or Vasoconstrictor?

Norepinephrine is a vasoconstrictor. It stimulates alpha receptors in the blood vessels and causes vasoconstriction (narrowing of the blood vessels). This raises the arterial blood pressure. This hormone is, therefore, used in people with life-threatening low blood pressure.

Impact on Heart Rate and Blood Pressure

Norepinephrine promotes vasoconstriction, which is a narrowing of the blood vessels. This effect, in turn, increases heart rate and blood pressure. Note: Both epinephrine and norepinephrine stimulate alpha-adrenoreceptors in the blood vessels, but norepinephrine has a greater effect.

Role In The Nervous System

In addition to the adrenal gland, norepinephrine is also made in a part of the brain called the locus coeruleus. Norepinephrine’s roles in the nervous system include regulating the sleep-wake cycle, attention, pain modulation, motor control, and energy balance. 

Stress Response Mechanism

The hormone norepinephrine is released by the adrenal glands in times of stress or anxiety as part of the body’s fight-or-flight response. It binds to adrenergic receptors throughout the body and brain, leading to an increase in alertness, a widening of the airways, dilation of the pupils, and an increase in heart rate and blood pressure. Along with epinephrine, norepinephrine initiates responses that improve the chances of survival during a critical fight-or-flight situation. 

Clinical Applications of Norepinephrine

Doctors use norepinephrine to increase systolic blood pressure in people with very low blood pressure. Norepinephrine may be used in the following situations:

• Critical hypotension. This is the medical term for dangerously low blood pressure (< 90/60 mm Hg). It can occur after a heart attack, for example, when a weak and damaged heart muscle cannot pump blood effectively. Norepinephrine can help to maintain blood pressure in such patients. 

• Pericardial tamponade. This is a condition in which fluid in the pericardium (the membrane surrounding the heart) makes it difficult for the heart to expand fully. Doctors remove the excess fluid using a needle and give norepinephrine as well. 

• Septic shock. This is a life-threatening condition in which the blood pressure drops to dangerously low levels due to a severe infection. Doctors use norepinephrine to raise blood pressure along with antibiotics to treat the infection.

• Neurogenic shock. Extensive damage to neurons can lead to problems maintaining stable blood pressure, heart rate, and temperature. Doctors use norepinephrine in this situation to regulate these vital parameters.

Epinephrine Overview

Role in "Fight or Flight" Response: What is the Main Function of Epinephrine?

The main function of epinephrine is to help the body mount a stress response. When the brain perceives danger, it stimulates the adrenal gland to increase the release of epinephrine into the bloodstream. Epinephrine acts on the autonomic nervous system and activates it. The autonomic nervous system is a part of the nervous system that regulates involuntary actions in the body such as blood pressure, heart rate, respiration, digestion, and arousal. The activation of the autonomic nervous system in threatening situations causes what is commonly called an adrenaline rush or fight or flight response. 

Impact on Heart Rate, Blood Pressure, and Blood Sugar Levels

Epinephrine activates alpha and beta receptors in almost all body tissues, including the heart, lungs, muscles, and blood vessels. As a result, epinephrine is responsible for redirecting blood flow to the heart and lungs, increasing heart rate, widening the breathing tubes, improving breathing, and raising blood sugar levels. Overall, these effects give you more energy, raise your focus and strength, and improve your overall physical performance so you can deal with an emerging threat or danger.

Effects on Carbohydrate Metabolism

The chemical messenger epinephrine increases the metabolic rate of carbohydrates. It breaks down fats and increases glucose levels in the body. This is achieved through increased glucose production in the liver, breakdown of stored glycogen, increased glucagon secretion, and decreased insulin secretion. 

Uses in Emergency Situations

Epinephrine is used to treat severe allergic reactions and severe asthma attacks. 

Clinical Applications of Epinephrine

Doctors use epinephrine to treat severe and potentially life-threatening allergic reactions and health conditions, such as:

• Anaphylactic shock. This is a severe and life-threatening allergic reaction that can interfere with breathing. It can occur due to an allergic reaction to foods, drug reactions, or bee stings. An epinephrine injection can be life-saving in people experiencing anaphylaxis. Epinephrine works by increasing the heart rate and blood pressure, improving blood flow, relaxing the muscles in the throat and airways, and making breathing easier. Some people who are at a high risk of anaphylaxis carry an epinephrine auto-injector, such as an EpiPen, with them at all times.

• Sudden asthma attacks. Doctors may give epinephrine in nebulized or other inhaled forms to prevent or treat severe asthma attacks.  

• Septic shock caused by severe infections. Epinephrine can be administered intravenously to correct very low blood pressure due to low levels of catecholamines.

• Cardiac arrest. Epinephrine increases blood pressure and blood flow to vital organs like the heart and brain in people with cardiac arrest.

Similarities: How Are Norepinephrine and Epinephrine Similar?

Epinephrine and norepinephrine are both chemical messengers that have similar chemical structures. Both hormones regulate the body’s sympathetic nervous system. This is a part of the nervous system that controls the body’s “fight or flight response” in a stressful situation. 

Norepinephrine and epinephrine act on the central nervous system and different organs in the body. They activate alpha and beta receptors in the brain and spinal cord. Having too much or too little epinephrine and norepinephrine can cause significant health problems. 

Medical Uses: When Do You Use Norepinephrine Vs. Epinephrine?

Epinephrine is used to treat a life-threatening allergic reaction (anaphylaxis), sudden asthma attack, and cardiac arrest. Epinephrine is also used to treat low blood pressure and slow heart rate. It is available in an autoinjector (Epi-Pen) for people who have a history of severe allergic reactions. 

Norepinephrine is used to treat life-threatening hypotension (low blood pressure) that can occur in people with certain medical conditions or during or after surgical procedures. Norepinephrine is also used during cardiopulmonary resuscitation (CPR) and to treat septic shock (a severe infection that can lead to organ failure). 

Clinical Uses

Scientists have used the properties of catecholamines to develop drugs and treatments. For example, the nasal decongestant pseudoephedrine is a sympathomimetic. It produces effects similar to the activation of the sympathetic nervous system and works by narrowing blood vessels in the nasal passages, thereby decreasing swelling and congestion.

Antidepressant medications called serotonin-norepinephrine reuptake inhibitors (SNRIs), for example, duloxetine (Cymbalta) and venlafaxine (Effexor XR), prevent the reuptake of serotonin and norepinephrine from nerve endings. They make more of the neurotransmitters available and relieve symptoms of depression.

The ability of norepinephrine to increase local blood flow may have applications in postsurgical patients. Studies have found that local infusion of norepinephrine reduces blood loss and the need for blood transfusions in people who have undergone total knee replacement surgery.

Implications of Too Much or Too Little Epinephrine and Norepinephrine

What Happens If You Have Too Little Epinephrine or Norepinephrine?

Norepinephrine is continuously released into the blood circulation to maintain blood pressure, while epinephrine is produced in response to stress. People with poor nutrition and chronic stress may have low levels of these hormones. Also, certain medications like methylphenidate (Ritalin) can make the body less sensitive to epinephrine and norepinephrine.

Low levels of epinephrine and norepinephrine can lead to various physical and mental health conditions, such as anxiety, depression, hypoglycemia (low blood sugar), fibromyalgia, migraines, sleep disorders, and restless legs syndrome. 

Dopamine beta-hydroxylase deficiency is a genetic disorder in which there is a lack of norepinephrine, resulting in low blood pressure, low blood glucose, and other health complications. 

What Happens If You Have Too Much Epinephrine and Norepinephrine?

Certain medical conditions can lead to an overproduction of epinephrine, norepinephrine, or both. This includes tumors of the adrenal glands such as pheochromocytoma or paraganglioma. Obesity and ongoing stress can also cause high levels of epinephrine and norepinephrine. Very rarely, medication dosing errors can lead to a norepinephrine or epinephrine overdose.

Too much epinephrine or norepinephrine in the body can lead to signs and symptoms such as anxiety, high blood pressure, heart palpitations, rapid heartbeat, weight loss, excessive sweating, and headaches. 

When To See a Doctor?

Most people can naturally maintain adequate levels of chemical messengers such as epinephrine or norepinephrine by eating a healthy diet, exercising regularly, getting enough sleep, and practicing meditation or other such activities for stress relief. If you struggle with chronic stress, your primary care team and wellness professionals can help you learn to manage stress responses better. 

If you have signs and symptoms that indicate hormonal imbalance, you should see a doctor. Your primary care physician may refer you to an endocrinologist, a doctor who specializes in hormonal disorders. They can evaluate you and help find out if something is going on with your norepinephrine or epinephrine levels.