the concentrations of the agonists required for half-maximum stimulation ( ec50 ) were approximately 1 nm ( isoproterenol ) , 8 nm ( epinephrine ) , 9 nm ( salbutamol ) and 2 microm ( norepinephrine ) giving an order of potency of isoproterenol greater than epinephrine = salbutamol much greater than norepinephrine .
C0014563
epinephrine
C0028351
norepinephrine