An agonist is a drug or an endogenous substance that binds to a Receptor (it has affinity for the receptor binding site) and produces a biological response (it possesses intrinsic activity). The binding of a drug agonist to the receptor produces an effect that mimics the physiological response observed when an endogenous substance (e.g., hormone, Neurotransmitter) binds to the same receptor. In many cases, the biological response is directly related to the concentration of the agonist available to bind to the receptor. As more agonist is added, the number of receptors occupied increases, as does the magnitude of the response. The potency (strength) of the agonist for producing the physiological response (how much drug is needed to produce the effect) is related to the strength of binding (the affinity) for the receptor and to its intrinsic activity. Most drugs bind to more than one receptor; they have multiple receptor interactions.
(See also: Agonist/Antagonist (Mixed) ; Antagonist )
Ross, E. M. (1990). Pharmacodynamics: Mechanisms of drug action and the relationship between drug concentration and effect. In A. G. Gilman et al (Eds.), Goodman and Gilman's the pharmacological basis of therapeutics, 8th ed. New York: Pergamon
Nick E. Goeders
1. (prime mover) a muscle whose active contraction causes movement of a part of the body. Contraction of an agonist is associated with relaxation of its antagonist.
2. a drug or other substance that acts at a cell-receptor site to produce an effect that is the same as, or similar to, that of the body's normal chemical messenger. Sympathomimetic drugs (alpha agonists and beta agonists) are examples.