Epinephrine

Overview
Pharmacological Targets
  • Epinephrine can stimulate all the adrenergic receptors including alpha and beta subtypes; however, its pharmacological effects depend on the dosage and route of administration as discussed below.
Pharmacological Effects
  • Vasculature
    • The vascular effects of epinephrine depend on the dosage and location as both vasoconstriction (mediated by Alpha1 Receptor) and vasodilation (mediated by Beta2 Receptor) are possible. Vasoconstriction predominates in the skin and kidneys whereas vasodilation predominates in the liver and skeletal muscle. Because beta2 receptors are more sensitive to epinephrine than alpha1 receptors, at low doses vasodilation predominates whereas at higher doses vasoconstriction predominates. Consequently, the effects of epinephrine on Systemic Vascular Resistance (SVR) are dosage dependent with low doses causing a slight drop in SVR and high doses causing a slight increase in SVR.
  • Cardiac Effects
    • Cardiac beta1 receptors are highly sensitive to epinephrine and thus both heart rate and contractility are stimulated, leading to an increase in cardiac output.
  • Blood Pressure
    • The effects of epinephrine on blood pressure emerge from its modulation of SVR and cardiac stimulatory properties. At moderate doses, the SVR decreases modestly and cardiac output is potently stimulated. These effects serve to increase systolic arterial pressure and lower diastolic pressure, yielding only modest increases in mean arterial pressure (MAP) and a widened pulse pressure. Because blood pressure only changes slightly, there is little stimulation of the baroreceptor reflex and compensatory cardiac vagal outflow as occurs with norepinephrine.
  • Respiratory Effects
    • Stimulation of beta2 receptor results in powerful bronchodilation and thus reduced airflow resistance.
  • Metabolic Effects
    • Epinephrine displays a number of metabolic effects including increased hepatic glycogenolysis and increased adipocyte lipolysis via beta receptors.
Therapeutic Uses
  • Today, epinephrine is used a rapid-acting broncholilator in contexts of anaphylaxis. It's local cutaneous injection, yielding powerful vasoconstriction, is also used to reduce bleeding during minor procedures.