Adrenaline (also known as epinephrine) is a hormone and neurotransmitter the sympathetic nervous system releases as part of the body’s “fight-or-flight” response. Adrenaline increases blood and oxygen flow to the muscles, releases stored energy from the liver and fat cells, and prepares the body for quick action.
Epinephrine is an amine hormone. It is produced and released by a region in the central part of the adrenal gland called the adrenal medulla. In a multistep process, enzymes convert the amino acid tyrosine into the chemical L-dopa, which is converted to dopamine and then converted to norepinephrine. Epinephrine is synthesized from norepinephrine (noradrenaline) and released into the bloodstream.
Together, epinephrine and norepinephrine are known as the catecholamines. Epinephrine makes up about 80% of the catecholamines that are released as part of the body’s stress response.
When the body is confronted with a dangerous or stressful situation (such as a test for which someone has not studied or an encounter with a dangerous-looking individual), the fight-or-flight response is initiated. In order to act quickly, the body diverts energy away from areas where it is not needed to those where it is most required, such as the heart and muscles.
When the body senses a threat, the hypothalamus in the brain releases nerve signals to the adrenal medulla to release epinephrine and norepinephrine.
When released, the epinephrine circulates around the body through the bloodstream until it reaches its target organs—the heart, blood vessels, liver, and fat cells. The hormone binds to two different types of receptors: alpha-adrenergic and beta-adrenergic receptors. Each of these receptors triggers a different action within cells. Alpha receptors initiate smooth muscle contraction and blood vessel constriction, whereas beta receptors stimulate the heart muscle.
The release of epinephrine causes the following reactions in the body:
- The heart beats faster, pumping additional blood throughout the body, and especially to the muscles, in preparation for action.
- Blood vessels constrict, raising the blood pressure.
- Small tubes in the lungs called bronchioles dilate to send more oxygen throughout the body.
- Glycogen (the stored form of glucose) is broken down into glucose in the liver and released.
- Fat stores are released from adipose tissue to be used for energy.
- Blood flow slows to the digestive tract, skin, and kidneys, where it is not needed as much.
The first people to identify the effects of epinephrine were British physician George Oliver (1841-1915) and endocrinologist Edward Albert Sharpey-Schafer (1850-1935). In 1894, they discovered that injecting an extract from the adrenal gland into the bloodstream of an animal raised its blood pressure. Then in 1901, Japanese chemist Jokichi Takamine (1854-1922) isolated and purified epinephrine from the adrenal medulla and patented it. British pharmacologist Henry Dale (1875-1968) began using the name adrenaline for the hormone.
Epinephrine can be isolated from the adrenal glands of animals and used for medical purposes. It can be injected into the heart to restart the heartbeats of people who are experiencing cardiac arrest. It can open the bronchioles of the lungs in people with asthma, or in those who have had severe allergic responses to food, medications, or other substances. Drugs called beta-blockers are often given to patients to reduce anxiety. These drugs block beta-adrenergic receptors, slowing the heart rate and lowering blood pressure.
Some people may experience a drug-like high from participating in behaviors that trigger the body’s fight-or-flight response. These people are sometimes referred to as “adrenaline junkies” or “adrenaline addicts”. For example, people who seek thrills, such as skydivers, mountain climbers, and extreme skiers, experience a rush of adrenaline from the knowledge that their actions could result in severe injury or even death. Compulsive gamblers often cite the reason for their addiction as less the desire to win than the physical rush they get from playing. Some people who steal feel that same type of adrenaline rush from the idea that they might be apprehended. The heightened sense of awareness, increased heartbeat, and rapid breathing that occur when the adrenal medulla releases adrenaline is similar to the high people experience when taking drugs, and it can be similarly addictive.
Adrenaline (epinephrine) —A hormone and neurotransmitter released by the adrenal gland as part of the body’s fight-or-flight response.
Adrenaline addiction —A drug-like response some people experience from participating in activities (such as skydiving or gambling) that trigger adrenaline release.
Beta-blockers —Drugs that block beta-adrenergic receptors to reduce the actions of epinephrine, thereby lowering the heart rate and blood pressure.
Bronchioles —Tiny tubes in the lungs.
Catecholamines —A class of hormones that includes epinephrine and norepinephrine, which are involved in the fight-or-flight response.
Enzymes —Proteins that trigger chemical reactions in the body.
Glycogen —The form of the sugar, glucose, that is stored in the liver and muscles.
Norepinephrine (noradrenaline) —A hormone produced by the adrenal gland, along with epinephrine, as part of the fight-or-flight response.
Tyrosine —The amino acid from which epinephrine is synthesized.
Church, Matt. Adrenaline Junkies and Serotonin Seekers: Balance Your Brain Chemistry to Maximize Energy, Stamina, Mental Sharpness, and Emotional Well-Being. Berkeley, CA: Ulysses Press, 2004.
Goldstein, David S. Adrenaline and the Inner World: An Introduction to Scientific Integrative Medicine. Baltimore, MD: The Johns Hopkins University Press, 2006.
Meyer, Jerrold S., and Linda F. Quenzer. Psychopharmacology: Drugs, the Brain and Behavior. Sunderland, MA: Sinauer Associates, 2004.
Adrenaline Addicts Anonymous. 350 South Center Street, Number 500, Reno, NV 89501. <http://www.adrenalineaddicts.org/>.
American Psychiatric Association. 1000 Wilson Boulevard, Suite 1825, Arlington, VA 22209-3901. Telephone: (703) 907-7300. <http://www.psych.org>.
National Alliance on Mental Illness. 2107 Wilson Boulevard, Suite 300, Arlington, VA 22201-3042. Telephone: (800) 950-6264. <http://www.nami.org>.
National Institute of Mental Health. 6001 Executive Boulevard, Room 8184, MSC 9663, Bethesda, MD 20892-9663. Telephone: (866) 615-6464. <http://www.nimh.nih.gov>.
Stephanie N. Watson
Alan W. Cuthbert.
See also adrenal glands; autonomic nervous system.