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==Mechanism of action==
[[Image:G protein signal transduction (epinephrin pathway).png|thumb|250px|β-adrenergic receptors]]
:''Further reading: [[adrenergic receptor]]''

Epinephrine's actions are mediated through adrenergic receptors. Epinephrine is a non-selective agonist of all adrenergic receptors. It activates α<sub>1</sub>, α<sub>2</sub>, β<sub>1</sub>,  and β<sub>2</sub> receptors to different extents.<ref name=pharmnemonics>{{Cite book | author=Shen, Howard | title=Illustrated Pharmacology Memory Cards: PharMnemonics | date=2008 | publisher=Minireview | isbn=1-59541-101-1 | pages=4}}</ref> Specific functions include:

* It binds to ''α<sub>1</sub> receptors'' of [[liver]] cells, which activate [[inositol-phospholipid signaling pathway]], signaling the phosphorylation of glycogen synthase and phosphorylase kinase (inactivating and activating them, respectively), leading to the latter activating another enzyme—glycogen phosphorylase—which catalises breakdown of glycogen (glycogenolysis) so as to release glucose to the bloodstream. Simultaneously protein phosphatase-1 (PP1) is inactivated, as in the active state PP1 would reverse all the previous phosphorylations.

* Epinephrine also activates ''β-adrenergic receptors'' of the liver and muscle cells, thereby activating the [[adenylate cyclase]] signaling pathway, which will in turn increase [[glycogenolysis]]. 

β<sub>2</sub> receptors are found primarily in [[skeletal muscle]] blood vessels where they trigger [[vasodilation]]. However, α-adrenergic receptors are found in most [[smooth muscle]]s and [[Intestine|splanchnic]] vessels, and epinephrine triggers [[vasoconstriction]] in those vessels.