Norepinephrine

Overview
  • Norepinephrine (NE) is the endogenous direct adrenergic agonist of the sympathetic nervous system secreted by postganglionic neurons on a variety of visceral target organs. It can also be administered as an IV infusion in pharmacological doses. Its pharmacological effects are discussed here.
Pharmacological Targets
  • Although NE can theoretically stimulate all of the adrenergic receptors, when given as at pharmacological doses, its effects are primarily through activation of alpha1 receptors.
Pharmacological Effects
  • Vasoconstriction
    • Because of its primarily alpha1 activity, NE results in diffuse vasoconstriction and thus an increase in systemic vascular resistance (SVR) which yields an increase in both systolic and diastolic systemic arterial pressure, and consequently mean arterial pressure (MAP). The vasoconstricting capacity of NE is greater than that of epinephrine or dopamine because NE does not strongly stimulate vasodilating beta2 receptors
  • Cardiac Effects
    • Although NE delivered endogenously by the sympathetic nervous system strongly stimulates the heart rate and cardiac contractility, pharmacological infusion of NE does not. This phenomenon is likely a result of the sharp increase in arterial pressure, activating carotid barorecetpors and thus resulting in a compensatory outflow of parasympathetic tone to the heart, counteracting any cardiostimulatory properties of the pharmacologically-delivered NE.
Therapeutic Uses
  • Pharmacological intravenous NE (Levophed) is typically the first-line treatment for maintaining systemic arterial pressure during states of septic shock.