Adrenergic receptors bind catecholamines to mediate many physiologic functions. The endogenous catecholamines include epinephrine, norepi­nephrine, and dopamine. Many drugs used to control blood pressure perioperatively act on adrenergic receptors. α-adrenergic receptors are activated by norepinephrine, epinephrine, and isoproterenol in descending order of responsiveness. β-adrenergic receptors demonstrate the inverse, with the greatest activity in response to isoproterenol, followed by epinephrine, and finally norepinephrine. Receptors that interact with dopamine are termed dopaminergic. Adrenergic receptors can be further subdivided based on their anatomic location and downstream effects: