Adrenergic antagonist

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 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. 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. There are three different types of antagonists. While only a few α-adrenergic antagonists are competitive, all β-adrenergic antagonists are competitive antagonists. Competitive antagonists are a type of reversible antagonists. A competitive antagonist will attach itself to the same binding site of the receptor that the agonist will bind to. Even though it is in activator region, the antagonist will not activate the receptor. This type of binding is reversible as increasing the concentration of agonist will outcompete the concentration of antagonist, resulting in receptor activation.