Receptor Concept & Drug-Receptor Interaction

Introduction

• Pharmacodynamics is the study of the biochemical, cellular and physiological actions of drugs and the molecular mechanisms by which they are produced — "what the drug does to the body"; it covers the action→effect sequence, the dose-effect relationship and drug interactions.
• Basic tenet — drugs (except gene-based therapies) do not impart new functions; they only alter the pace (rate/magnitude) of ongoing physiological processes (stimulation, depression, irritation, replacement, cytotoxic action).
• The receptor concept is the "big idea" of pharmacology. Ehrlich's dictum "Corpora non agunt nisi fixata" — a drug will not act unless it is bound; pharmacological effect requires non-uniform (bound) distribution.
• A receptor is a macromolecule/binding site that recognises a signal molecule (endogenous mediator or drug) and initiates the response, but itself has no other function. A ligand is any molecule that binds a receptor (agonists and antagonists are both ligands).