Pharmaceutical Chemistry

Receptor Agonist/ Antagonist

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Receptors are transmembrane proteins that enable the transfer of chemical signals from the cellular outer microenvironment into the cells, as well as within the cell. An agonist is a mimetic of the natural ligand and produces a similar biological effect as the natural ligand when it binds to the receptor. Agonists bind to the receptor at the same binding site as the natural ligand, and results in either a full (conventional agonists) or partial (partial agonists) activation. Receptor antagonists are inhibitors of receptor activity. Antagonists mimic ligands that bind to a receptor and prevent receptor activation by a natural ligand. Preventing activation may have many effects. Where subtypes of receptors occur, it is possible that a single ligand can have agonist and antagonist properties (i.e. mixed pharmacology). Some of the best illustrations of this occur in opioid receptors of which there are three classical subtypes: μ, δ and κ. For example, pentazocine is an antagonist at μ and an agonist at δ/κ opioid receptors