Classification Of The Alpha Adrenoceptor

[motivationG]

Right im so confused because in my lecture notes it says that the classification of the alpha adrenoceptor in terms of agonist potency is as follows:

adrenaline > noradrenaline >> isoprenaline

Whereas in a book i'm seeing that the classification of the alpha adrenoceptor is
noradrenaline > adrenaline > isoprenaline

I'm wondering if anyone actually knows the answer?
thanks in advance!!

[Gilli-chan]

According to Rang & Dale, it's NA>ADR>ISO for alpha and ISO>ADR>NA for beta. I trust Rang & Dale personally Hope with more Reading it gets a little clearer - I found all the alpha/beta stuff really confusing for ages, but I think (HOPE!) I've got it sussed now! Good luck

[gdent]

Right im so confused because in my lecture notes it says that the classification of the alpha adrenoceptor in terms of agonist potency is as follows:

adrenaline > noradrenaline >> isoprenaline

Whereas in a book i'm seeing that the classification of the alpha adrenoceptor is
noradrenaline > adrenaline > isoprenaline

I'm wondering if anyone actually knows the answer?
thanks in advance!!

It's not that straightforward, unfortunately. Adrenaline and noradrenaline are approximately equipotent at alpha-1 and beta-3 receptors, adrenaline is more potent than noradrenaline at alpha-2 and beta-2 receptors, noradrenaline is more potent than adrenaline at beta-1 receptors.

In general, noradrenaline has high potency at postsynaptic receptors in tissues with sympathetic innervation (alpha-1 and beta-1), while adrenaline has high potency at receptors on presynaptic nerve endings (alpha-2) and in tissues without sympathetic innervation (beta-2). Again, it's not quite this simple in fact but it's a fairly good point to start.