the adrenergic receptors ( ars ) ( subtypes alpha 1 , alpha 2 , beta 1 , and beta 2 ) are a prototypic family of guanine nucleotide binding regulatory protein-coupled receptors that mediate the physiological effects of the hormone epinephrine and the neurotransmitter norepinephrine .
C0014563
epinephrine
C0028351
norepinephrine