competition binding experiments revealed that these low affinity sites were distinct from adrenergic receptors : the catecholamine agonists ( - ) - and ( - ) -epinephrine , ( - ) -norepinephrine , ( - ) -isoproterenol and dopamine competed with similar ki values ( microm range ) whereas clonidine did not interact .
C0007412
catecholamine
C0022245
isoproterenol