Epinephrine is an α agonist that has several pharmacologic effects. It acts on α1 adrenergic receptors to constrict smooth muscle of resistance blood vessels, such as those in the skin and splanchnic beds, causing increased peripheral resistance and venous return.
Epinephrine acts on both β1 and β2 adrenergic receptors and acts to increase heart rate and contractility. Furthermore, it increases lipolysis and renin release, while causing vasodilation. Drugs acting on β receptors also decrease uterine tone.
Epinephrine is indicated for hypotension, as it increases systolic pressure as a result of positive inotropic and chronotropic effects on the heart. At high doses, it may cause vasoconstriction within skeletal muscle vasculature.
This drug is used during anaphylactic shock and asthma attacks because of its vasoconstrictive effects, reversing angioedema and hypotension. Stimulation of β2 receptors causes bronchodilation as well as increasing intracellular cyclic adenosine monophosphate production in mast cells and basophils, reducing release of inflammatory mediators.
Patients with allergies undergoing immunotheraphy may be administered epinephrine to reduce possible immune response to the allergen.
Epinephrine acts in the eye as a less selective alpha agonist and decreases aquous humor production through vasoconstriction of ciliary body blood vessels. This decreases ocular pressure in open-angle glaucoma.Note: Epinephrine should NOT be used in closed-angle glaucoma.
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