norepinephrine ( 0.068-2.27 nmol/ml ) demonstrated a loss of the original vasoconstrictor activity , in a pattern similar to histamine and epinephrine , while higher doses of norepinephrine ( 0.34-9.1 nmol/ml ) demonstrated no change in activity with a left shift in the concentration at which the maximal responses occurred , suggesting an increase in sensitivity as a result of repeated exposure .
C0014563
epinephrine
C0028351
norepinephrine