What is epinephrine?
Epinephrine, also called adrenaline, is both a hormone and a neurotransmitter. As a hormone, it’s made and released by your adrenal glands, which are hat-shaped glands that sit on top of each kidney. As a central nervous system neurotransmitter, it’s a chemical messenger that helps transmit nerve signals across nerve endings to another nerve cell, muscle cell or gland cell.
Epinephrine is part of your sympathetic nervous system, which is part of your body’s emergency response system to danger — the “fight-or-flight” response. Medically, the flight-or-flight response is known as the acute stress response.
Epinephrine is also called a catecholamine, as are norepinephrine and dopamine. They’re given this name because of a certain molecule in its structure. As a hormone, epinephrine is made from norepinephrine inside of your adrenal gland.
What does epinephrine do in the body?
As a neurotransmitter, epinephrine plays a small role. Only a small amount is produced in your nerves. It plays a role in metabolism, attention, focus, panic and excitement. Abnormal levels are linked to sleep disorders, anxiety, hypertension and lowered immunity.
Epinephrine’s major action is in its role as a hormone. Epinephrine is released by your adrenal glands in response to stress. This reaction causes a number of changes in your body and is known as the fight-or-flight response.
What’s the fight-or-flight response?
The fight-or-flight response refers to your body’s response to a stressful situation, such as needing to escape danger (moving away from a growling dog) or facing a fear (giving a speech for school or work). The term comes from the choice our ancestors faced when confronted with a dangerous situation — to stay and fight or run to safety.
During the fight-or-flight response, you (your brain) perceive danger. Next, nerves in an area of your brain called the hypothalamus send a signal down your spinal cord, then out to your body. The neurotransmitter that transmits your brain’s nervous system message of what to do is norepinephrine (noradrenaline). The neurotransmitter noradrenaline reaches the following organs and tissues and causes these rapid body reactions:
- Eyes: Pupils dilate to let more light in to better see more of your surroundings.
- Skin: Skin turns pale as blood vessels receive a signal to divert blood to areas more in need of your blood’s oxygen, such as your muscles, so you can fight or run away.
- Heart: Heart pumps harder and faster to deliver more oxygenated blood to areas most in need, like your muscles. Blood pressure also increases.
- Muscles: Muscles receive more blood flow and oxygen so they can react with greater strength and speed.
- Liver: Stored glycogen in your liver is converted to glucose to provide more energy.
- Airways: Breathing is deeper and faster. Your airways open up so more oxygen is delivered to the blood, which goes to your muscles.
The neurotransmitter noradrenaline also reaches your adrenal gland, which releases the hormones adrenaline (epinephrine) and noradrenaline (norepinephrine). These hormones travel through your blood to all parts of your body. They reach your eyes, heart, airways, blood vessels in your skin and your adrenal gland again. The “message” to these organs and tissues is to continue to do react until you’re out of danger.
This is a simple description of the fight-or-flight response. Other parts of your nervous system are also involved, as well as other organ systems, hormones and neurotransmitters.
How is epinephrine used as a medication?
When used as a medication, synthetic epinephrine is used to treat:
- Cardiac arrest/cardiopulmonary resuscitation (CPR): Epinephrine stimulates your heart.
- Eye surgery: Epinephrine helps keep your pupils dilated.
- Septic shock: Epinephrine increases your blood pressure.
- Asthma: Epinephrine opens airways and decreases airway spasms.
- Anaphylaxis: Epinephrine relaxes airway muscles. It’s the first-response treatment for this severe, life-threatening allergic reaction.
What are the side effects of epinephrine as a medication?
Side effects of epinephrine as an aerosol or injection that require medical attention include:
- Allergic reactions like skin rash, itching or hives, swelling of your face, lips or tongue.
- Breathing problems.
- Chest pain.
- Fast heartbeat.
- High blood pressure.
- Trouble passing urine or change in the amount of urine.
- Trouble sleeping.
- Pain, tingling, numbness in your hands or feet.
- Pain, redness, or irritation at site where injected.
Plus the first five side effects listed under “aerosol” above.
What health conditions result from low levels of epinephrine?
Health conditions that result from low levels of epinephrine include:
- Sleeping problems.
- Low blood sugar (hypoglycemia).
- Changes in blood pressure, heart rate.
What health conditions result from high levels of epinephrine?
Health conditions that result from high levels of epinephrine include:
- High blood pressure (hypertension).
- Rapid or irregular heartbeat.
- Excessive sweating.
- Cold or pale skin.
- Severe headaches.
- Nervous feeling, jitters.
- Epinephrine overdose, which can lead to high blood pressure, stroke and death.
- Pheochromocytoma, which is an adrenal gland tumor.
What are the similarities and differences between epinephrine and norepinephrine?
|Epinephrine (adrenaline)||Norepinephrine (noradrenaline)|
|Neurotransmitter (NT)||Yes||Yes, it’s the most common NT of your sympathetic nervous system; mainly works as an NT|
|Hormone||Yes, mainly works as a hormone||Yes|
|Part of fight-or-flight response||Yes||Yes|
|Made in/released from||Mainly in and from the adrenal glands||Mainly in and from the nerves|
|Works on/action||Acts on almost all body tissues||Mainly works to increase or maintain blood pressure|
|When released into bloodstream||During times of stress||Continuously|
|Common use in medicine||Severe asthma, anaphylaxis, low blood pressure from severe conditions||Emergency low blood pressure conditions|
A note from Cleveland Clinic
Epinephrine is both a neurotransmitter and a hormone, but it acts mainly as a hormone. Epinephrine, also known as adrenaline, plays an important role in your body’s fight-or-flight response. It’s also used as a medication to treat many life-threatening conditions.
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