This document discusses adrenergic antagonists, which are drugs that inhibit the function of adrenergic receptors. There are five adrenergic receptors divided into two groups - beta receptors (β1, β2, β3) and alpha receptors (α1, α2). Adrenergic antagonists reduce or block signals from adrenergic agonists. The effects of alpha and beta antagonists differ. Alpha antagonists cause vasodilation by blocking alpha receptors that cause vasoconstriction, while beta antagonists diffuse through the GI tract and bind to proteins before metabolizing in the liver or being eliminated unchanged. Examples of alpha and beta antagonists are provided.

1. Adrenergic antagonist
by
Dr. Amit K. Keshari
Assistant Professor
Faculty of Pharmaceutical Sciences,
RAMA University,
Kanpur, Uttar Pradesh

2. An adrenergic antagonist is a drug that inhibits the function of adrenergic receptors. There
are five adrenergic receptors, which are divided into two groups. The first group of receptors
are the beta (β) adrenergic receptors.
There are β1, β2, and β3 receptors. The second group contains the alpha (α) adrenoreceptors.
There are only α1 and α2 receptors. Adrenergic receptors are located near
the heart, kidneys, lungs, and gastrointestinal tract. There are also α-adreno receptors that
are located on vascular smooth muscle.
Antagonists reduce or block the signals of agonists. They can be drugs, which are added to
the body for therapeutic reasons, or endogenous ligands. The α-adrenergic antagonists have
different effects from the β-adrenergic antagonists.
Adrenergic antagonist

4. Adrenergic ligands are endogenous proteins that modulate and evoke
specific cardiovascular effects. Adrenergic antagonists reverse the natural cardiovascular effect,
based on the type of adrenoreceptor being blocked. For example, if the natural activation of the
α1-adrenergic receptor leads to vasoconstriction, an α1-adrenergic antagonist will result
in vasodilation.[3]
Some adrenergic antagonists, mostly β antagonists, passively diffuse from the gastrointestinal
tract. From there, they bind to albumin and α1-acid glycoprotein in the plasma, allowing for a
wide spread through the body. From there, the lipophilic antagonists are metabolized in the liver
and eliminated with urine while the hydrophilic ones are eliminated unchanged.[4]

5. Examples
Alpha blockers
•Phentolamine
•phenoxybenzamine
Beta blockers
•Propranolol
•Nebivilol
•Atenolol
•Oxprenolol
•Metoprolol
•Timolol
•Pindolol
•Nadolol
•Pindolol
•Esmolol
•Acebutolol
•Sotalol
•Talinolol
•Betaxolol