They are structurally the same, except that epinephrine has an N-methyl group that nor-epi does not. But they do have very similar functions.
👍 PNMT is expressed higher in the presence of cortisol,
Nor --- (PNMT) --> Epi
Penylethanolamine N-Methyl Transferase
They act differently on different receptors. Beta 2 receptors love Epi, Alpha 1 have greater affinity for epi too, beta 1 have equal affinity (increase heart rate), alpha 2 have great nor affinity.
Nor only works in the the sympathetic nervous system while epi is in the sympathoadreanal nervous system.
Similar NTs yet peculiar specifics, you will probably learn more about in med school. In general alpha receptors deal more with constriction and excitatory responses, while beta deal more with dilatory and relaxation responses.
When you hemorrhage (over 12% blood loss), the beta 2 receptors (epi) play a big role in making sure you don't die!
Dopamine is the precursor of epi and norepi synthesis.
dopamine --> nor ----> epi
The enzymes are tyronsine hydroxylase and PNMT, the original amino acid is tyrosine (i forget the dopamine enzyme).
