Saturday, 19 July 2008

What's the difference between adrenaline (epinephrine) and noradrenaline (norepinephrine)?

Confusingly, the substance called adrenaline by most of the world is known as epinephrine to Americans. Similarly, arenaline's cousin, noradrenaline is correspondingly known as norepinephrine. This proliferation of terminology would make this post too confusing, so I'm going to stick with adrenaline and noradrenaline here. (Apologies to American readers!)

[As an aside: why the dual names? I had no idea, but Professor Wikipedia assures me that an American company called Parke-Davis & Co. somehow managed to market a concentrated form of adrenaline under the name... Adrenalin. Since this was a little too close, name-wise, to the generic name for the substance, it was decided to switch the generic name to epinephrine. The choice was actually quite clever, since adrenaline is derived from the Latin ad (above) + renes (the kidney). Epinephrine is just the (ancient) Greek version of this, with epi + nephros meaning exactly the same thing.]

But back to the topic. For one, they are obviously chemically distinct - adrenaline is produced by the body via a modification of noradrenaline. Just what is changed isn't important in the slightest, so I won't go on about this aspect.

Secondly, they are used in slightly different places. Noradrenaline is used in the postganglionic neurones of the sympathetic nervous system. It is also used as a neurotransmitter, which obviously implies that it is generated within the neurones of the brain too. Adrenaline is largely produced by the adrenal medulla, although this structure does also produce some noradrenaline.

Lastly, while related, their functions differ somewhat. You may know that there are several types of receptors for adrenaline. For instance α1 receptors are found on blood vessels and stimulation leads to their constriction. On the other hand, β1 receptors are located on the heart, and their stimulation leads to an increase in the rate and force of the heart's contraction. Adrenaline is rather nonspecific, stimulating α, β1 and β2 receptors more or less equally. By contrast, noradrenaline exerts predominantly α activity, although it does stimulate the β to a lesser degree. Also, as mentioned, noradrenaline acts as a neurotransmitter in the brain too, playing a role in alertness, arousal and reward pathways.

There's considerably more detail out there on this topic, but, again, I can't see its use unless you happen to be doing a PhD!

25 comments:

  1. Norepinephrine and epinephrine are only located in the brain, adrenaline and noradrenaline are located in the body (and the brain if you arent american).

    the reason for the distinction is that they have entirely different functions. High epinephrine is not associated with aggression/height of senses/etc. like an "adrenaline" rush. Most of the main neurotransmitters (amines) are mostly located in the brain so it just made it more clear. Plus, the chemicals are not free to flow back and fourth because of the blood brain barrier.
    in a sense, they might as well be separate in psychology/neuroscience, but probably not if you are a chemist.

    they are considered different once they pass the blood brain barrier.

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  2. Hi Doug,

    I liked the emphasis you placed on distinguishing norepinephrine's effects in the brain from those in the rest of the body. As you say, to a chemist the molecules are identical, but to a physiologist the two molecules might as well be totally distinct.

    I'm not sure you're right about the terminology though. Adrenaline is totally synonymous with epinephrine, as is noradrenaline with norepinephrine. The reason for the confusion has been alluded to in my post, but you can read a litle more about it here.
    I've also got several books on neuroscience published in Britain, and they only refer to the molecule as "noradrenaline". Only the American (and I suppose, those countries following America's lead, such as Canada?) textbooks call the neurotransmitter "norepinephrine".

    Of course, from a distance such a dispute is frustratingly pointless. What's in a name?

    [As an aside, there are actually a few adrenergic neurones too, but these really are few in number, so I left them out of the original post.]

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  3. For instance, compare this, from "Clinical Pharmacology and Drug Therapy" (3rd edn.), written by two British pharmacologists:

    "Tricyclic antidepressants inhibit the re-uptake of noradrenaline and 5-hydroxytryptamine (5-HT) at central monoaminergic synapses. The relative potency of inhibition of noradrenaline and 5-HT re-uptake varies from drug to drug..."


    ... with this, from the famous "Textbook of Medical Physiology" (10th edn.) by Guyton and Hall, both Americans:

    "Norepinephrine is secreted by the terminals of many neurons whose cell bodies are located in the brain stem and hypothalamus. ... Norepinephrine is also secreted by most of the postganglionic neurons of the sympathetic nervous system..."

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  4. Thanks for the great explanation; saved me from breaking out my textbook to review, and taught me something new about the origin of the names!

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  5. @jeremy
    can u pl explain the point in the comparison ure tryin to make?

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  6. Not sure I follow Shobuj...?

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  7. @jeremy
    i take my question back, i got it :)
    Thanks

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  8. HI I would like to ask adrenaline targets the muscles or heart?and noradrenaline targets the heart or muscles?

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  9. On the name issue - an anaesthetist (note the spelling) pointed out that epinephrine is rather similar to ephedrine (used to reverse the hypotensive affects of epidurals).

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  11. thanks 4 explaing...thanks once again

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  13. Your comment is awaiting moderation.

    thaanxxx for the article… This was very helpful for me….
    i can give u some more details… Both norad and adrenaline increases BP, but by different mechanism…
    > Adreanaline increases BP by constricting blood vessles
    >Noradrenaline Increases BP by increasing HR > thereby, Increase Impulse conduction > increase contraction > Increasing volume expelled> thus increasing BP

    > Noradrenaline causes: (i) constriction of the cutaneous vessels; (ii) constriction
    of the vessels in skeletal muscle (adrenaline causes transient vasodilatation);
    (iii) bradyeardia (adrenaline causes tachycardia); (iv) rise in both
    systolic and diastolic pressures (adrenaline causes a rise in systolic pressure and
    either does not effect or causes a slight fall in diastolic pressure).

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  14. Epinephrine (adrenaline) and norephrine are both secreted by the medulla of the adrenal glands

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  15. Simple explanation, easy to comprehend.

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  16. heyyyyyyyyy thank u so much. it's really in easy language for the students

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  17. This is such a useful site for students - THANK YOU SO MUCH!

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  18. nice article

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  19. Both Epinephrine and Norepinephrine are sympathetic amines which stimulates alpha and beta receptors. Norepinehrine is released by adrenergic neurons as "neurotransmitters"; these neurons are found in the CNS and also in the sympathetic nervous system, whereas, epinephrine is synthesized from tyrosine in the adrenal medulla along with small quantities of Norepinephrine. Epinephrine increase BP b/c it has apositive inotropic and chronotropic effect on the heart, therefore cardiac output increases and also it causes vasoconstriction while Norepinephrine increases BP b/c its effect on alpha-1 receptor is pronounced and causes intense vsoconstriction, including the kidney causing and increase in the peripheral resistance, therfore increases BP..

    from;
    -KO

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  20. So if a patient has very low BP (77/55), but a high heart rate (90), the best drug would be Noradrenaline?

    Other options in the question are:

    Dobutamine
    Isoprenaline
    Adrenaline
    Atropine

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  21. goooooooooooooood xplanation

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  22. I'm American and I don't know anyone who says "epinephrine" or "norepinephrine." We just call it adrenaline over here. Just thought I'd throw that out there.

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  23. Thank you so much guys.....u all cleared my doubts....

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  24. Thank you so much guys.....u all cleared my doubts....

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