the potencies of alpha-adrenergic compounds to displace [ 3h ] clonidine binding ranked as follows : yohimbine greater than phentolamine much greater than prazosin for antagonists and clonidine greater than epinephrine greater than norepinephrine greater than phenylephrine much greater than amidephrine for agonists .
C0014563
epinephrine
C0028351
norepinephrine