the order of potencies of alpha-adrenoceptor agonists for inducing constriction was in canine arteries : epinephrine greater than norepinephrine = phenylephrine much greater than clonidine much greater than tyramine much greater than xylazine , in simian arteries : epinephrine greater than norepinephrine greater than phenylephrine greater than clonidine much greater than tyramine greater than or equal to xylazine , in canine veins : epinephrine greater than norepinephrine greater than phenylephrine greater than clonidine greater than or equal to xylazine much greater than tyramine , and in simian veins : norepinephrine = epinephrine greater than phenylephrine greater than clonidine greater than xylazine much greater than tyramine .
C0028351
norepinephrine
C0014563
epinephrine