Adrenergic receptor

In biochemistry, adrenergic receptors are cell surface receptors of the G-protein-coupled receptor type that are in the sympathetic nervous system and are "cell-surface proteins that bind epinephrine and/or norepinephrine with high affinity and trigger intracellular changes. The two major classes of adrenergic receptors, alpha and beta, were originally discriminated based on their cellular actions but now are distinguished by their relative affinity for characteristic synthetic ligands. Adrenergic receptors may also be classified according to the subtypes of G-proteins with which they bind; this scheme does not respect the alpha-beta distinction."

Classification

alpha-Adrenergic Receptors

alpha-1 receptors

Alpha-1 adrenergic receptors are a "subclass of alpha-adrenergic receptors (Receptors, Adrenergic, alpha). Alpha-1 Adrenergic receptors can be pharmacologically discriminated, e.g., by their high affinity for the agonist phenylephrine and the antagonist prazosin. They are widespread, with clinically important concentrations in the liver, the heart, vascular, intestinal, and genitourinary smooth muscle, and the central and peripheral nervous systems." Their functions include vasoconstriction.

Agonists, such as phenylephrine, are used to treat nasal congestion by causing vasoconstriction. Midodrine is an agonist that is used for orthostatic hypotension and hepatorenal syndrome.

Antagonists, such as prazosin, are used to treat hypertension by blocking vasoconstriction.

alpha-2 receptors

Alpha-2 adrenergic receptors are a "subclass of alpha-adrenergic receptors (Receptors, adrenergic, alpha). Alpha-2 Adrenergic receptors can be pharmacologically discriminated, e.g., by their high affinity for the agonist clonidine and the antagonist yohimbine. They are found on pancreatic beta cells, platelets, and vascular smooth muscle, as well as both pre- and postsynaptically in the central and peripheral nervous systems."

Genetic polymorphisms of alpha-2C (ADRA2C) may affect the response to adrenergic beta-antagonist treatment of heart failure.

Agonists, such as clonidine, are used to treat hypertension.

Antagonists, such as yohimbine, are used to treat erectile dysfunction.

beta-Adrenergic Receptors

beta-1 receptors

Beta-1 adrenergic receptors are a "subclass of beta-adrenergic receptors (receptors, adrenergic, beta). Beta-1 adrenergic receptors are equally sensitive to epinephrine and norepinephrine and bind the agonist dobutamine and the antagonist metoprolol with high affinity. They are found in the heart, juxtaglomerular cells, and in the central and peripheral nervous systems."

Adrenergic beta-agonists such as dobutamine, are used to treat circulatory shock by increasing heart contractility.

Adrenergic beta-antagonists that are selective for the beta-1 receptor such as metoprolol and atenolol, are used to treat hypertension and tachyarrythmias.

Abnormal genetic polymorphism of the beta-1 receptor may affect responses to adrenergic beta-antagonists in the treatment of heart failure and in preventing cardiac complications during perioperative care.

beta-2 receptors

Beta-2 adrenergic receptors are a "subclass of beta-adrenergic receptors (receptors, adrenergic, beta). Beta-2 Adrenergic receptors are more sensitive to epinephrine than to norepinephrine and have a high affinity for the agonist terbutaline. They are widespread, with clinically important roles in skeletal muscle, liver, and vascular, bronchial, gastrointestinal, and genitourinary smooth muscle." Their functions include vasodilation.

Adrenergic beta-agonists, such as terbutaline, are used to treat asthma by preventing bronchoconstriction.

beta-3 receptors

Beta-3 adrenergic receptors are a "subclass of beta-adrenergic receptors (receptors, adrenergic, beta). Beta-3 adrenergic receptors are the predominant beta-adrenergic receptor type expressed in white and brown adipocytes and are involved in modulating energy metabolism and thermogenesis."

See also

• sympathetic nervous system
• Acetylcholine receptor