Racepinephrine

Epinephrine is a non-selective agonist at α- and β-adrenergic receptors, which are all G-protein-coupled receptors. The main therapeutic effect of epinephrine arises from its agonist action on β2-adrenergic receptors, which activate adenylyl cyclase and increase intracellular cyclic AMP production. Epinephrine causes smooth muscle relaxation on various tissues, including bronchial smooth muscles. As a result, epinephrine serves to alleviate bronchospasm, wheezing and tightness of chest that may occur during asthmatic attacks. Via its relaxer effects on the smooth muscle of the stomach, intestine, uterus and urinary bladder, epinephrine may also alleviate pruritus, urticaria, and angioedema and may relieve gastrointestinal and genitourinary symptoms associated with anaphylaxis.

Epinephrine also acts on the α-adrenergic receptors on vascular smooth muscles, particularly in the skin and splanchnic vascular beds, to cause constriction. Epinephrine is thought to reduce capillary leakage by constricting precapillary arterioles, reducing hydrostatic pressure and consequently bronchial mucosal edema.