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What is Adrenergic?

By Vasanth S.
Updated Feb 18, 2024
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Adrenergic is a term used to describe proteins and drugs that interact with adrenaline or noradrenaline, also known as epinephrine and norepinephrine, respectively. For example, adrenergic receptors are membrane proteins that are the target for epinephrine and norepinephrine, while adrenergic transporters are proteins that carry norepinephrine across the cell membrane of nerve cells. An adrenergic agonist is a drug that typically produces the same effect as epinephrine or norepinephrine, where as an adrenergic antagonist is a drug that generally blocks the effects of epinephrine and norepinephrine. Epinephrine and norepinephrine act as hormones and neurotransmitters in numerous biological processes.

When epinephrine is released, it contracts and relaxes smooth muscle in the air passageways and arteries, typically resulting in deep breathing and increased blood pressure. Epinephrine can also increase the level of glucose and fatty acids in the blood, generally leading to increased energy production within cells. In addition, epinephrine and norepinephrine initiate the flight-or-fight response.

Norepinephrine typically increases the heart rate and blood flow to muscles during stressful situations and affects the part of the brain that is responsible for attention and response. It also increases blood glucose levels, thus providing needed energy for cells. Norepinephrine also acts as an anti-inflammatory agent when it is released as a neurotransmitter between nerve cells of the brain.

Epinephrine and norepinephrine bind to either an alpha or a beta adrenergic receptor to carry out its function. Alpha receptors are responsible for smooth muscle contractions and neurotransmitter inhibition, while beta receptors relax smooth muscles and contract the heart muscle. There are two subtypes of alpha receptors and three subtypes of beta receptors, each with their own agonist and antagonist.

Many alpha 1 receptor agonists, including methoxamine and oxymetazoline, typically target the phospholipase component of the receptor to generate the same effect as epinephrine and norepinephrine. Clonidine and guanabenz are alpha 2 receptor agonists that produce the same effect as epinephrine and norepinephrine by inhibiting the adenylyl cyclase component of the receptor. Drugs that block the effects of epinephrine and norepinephrine on alpha 1 and alpha 2 receptors include alfuzosin and atipamezole.

Beta 1 adrenergic receptor agonists, such as dobutamine and isoproterenol, stimulate adenylyl cyclase activity to open calcium ion channels in the heart muscle, while beta 2 agonists stimulate adenylyl cyclase to close calcium ion channels in smooth muscles. Beta 3 agonists, such as amibegron and solabegron, stimulate adenylyl cyclase to increase the production of fatty acids. Beta adrenergic receptor antagonists, also called beta blockers, include metoprolol and butoxamine.

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Discussion Comments

By indigomoth — On Nov 14, 2011

@pastanaga - Beta blockers are also used by athletics I believe. I've heard of them being used by archers at any rate.

I can imagine why, in a professional competition, it might be tempting to take a pill that can remove the symptoms of anxiety. You might even be able to justify it that it's not actually enhancing your performance, it's just taking away your fear.

You know, it's even been said that taking beta blockers after a traumatic event can help prevent a person from developing PTSD.

But, it's still considered an unfair advantage, so they've banned it from most professional competition now.

By pastanaga — On Nov 13, 2011

@umbra21 - Actually, beta blockers are supposed to be quite safe for long term use, because they are meant to be used for heart conditions, like arrhythmia that need the heart to slow down.

I think most adrenergic inhibitors are relatively safe.

I know that beta blockers have been used by musicians for a long time in order to enhance their performance by calming anxiety. This can help, for example, to steady their hands.

But, apparently there is a different quality to the music, if the musician is on beta blockers. People say that it is more flat, and less passionate.

I suppose that makes sense, as the heart beat might help people to regulate their timing when performing.

By umbra21 — On Nov 12, 2011

I had never heard of beta blockers before I took a chemistry course a few years ago, but now it seems that they are all the rage. I've seen them mentioned in movies and in books and all.

Generally it's from a character taking a beta blocker in order to maintain their cool. Like in a detective film, where someone is working undercover, they might take beta blockers to ensure their heart rate doesn't go up and make them look too nervous.

I think that in one House episode a patient was taking beta blockers for that reason and it threw off the diagnosis.

Personally I would be quite worried about my long term health if I was having to take beta blockers all the time.

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