What is (are) the KEY difference (s) between epinephrine and norepinephrine?

Question

I know there's some bio buffs out there...!

Answer 1

First of all, the answer above is totally wrong. They're both symathetic adrenergics and will both facilitate the fight-or-flight physiological response -- thus, norepinephrine does not "calm the body down to normal", and the wikipedia citations do not support such a claim.

The first major difference is in their synthesis. Norepinephrine (NE) is derived from dopamine-precursors by the enzyme dopamine-beta-hydroxylase, which occurs in neurons. Epinephrine (Epi) is a derivative of NE, catalyzed by the enzyme phenylethanolamine-N-methyltransferase, which converts NE to Epi -- this occurs in chromaffin cells in the adrenal medulla, and NOT in neurons.

The second major difference is that NE is released from nerve terminals, in close proximity to the post-synaptic receptor, and diffuses across the cleft to activate them in that fashion. Epi is released from the adrenal gland into the blood and flows to whatever receptors it will eventually activate -- i.e. it is NOT released by the neurons themselves.

The third major difference is that Epi has much higher binding affinity for the beta-2 receptor than does NE. This is important for pharmacophysiological reasons, but not for much else.

Answer 2

Epinephrine speeds up the body systems and norepinephrine calms the body systems and returns them to normal.