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An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. Whereas an agonist causes an action, an antagonist blocks the action of the agonist and an inverse agonist causes an action opposite to that of the agonist. == Types of agonists == Receptors can be activated by either endogenous (such as hormones and neurotransmitters) or exogenous (such as drugs) agonists, resulting in a biological response. A physiological agonist is a substance that creates the same bodily responses but does not bind to the same receptor. An endogenous agonist for a particular receptor is a compound naturally produced by the body that binds to and activates that receptor. For example, the endogenous agonist for serotonin receptors is serotonin, and the endogenous agonist for dopamine receptors is dopamine.〔Goodman and Gilman's Manual of Pharmacology and Therapeutics. (11th edition, 2008). p14. ISBN 0-07-144343-6〕 A superagonist is a compound that is capable of producing a greater maximal response than the endogenous agonist for the target receptor, and thus has an efficacy of more than 100%. This does not necessarily mean that it is more potent than the endogenous agonist, but is rather a comparison of the maximum possible response that can be produced inside the cell following receptor binding. Full agonists bind (have affinity for) and activate a receptor, producing full efficacy at that receptor. One example of a drug that acts as a full agonist is isoproterenol, which mimics the action of adrenaline at β adrenoreceptors. Another example is morphine, which mimics the actions of endorphins at μ-opioid receptors throughout the central nervous system. Partial agonists (such as buspirone, aripiprazole, buprenorphine, or norclozapine) also bind and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonist, even at maximal receptor occupancy. Agents like buprenorphine are used to treat opiate dependence for this reason, as they produce milder effects on the opioid receptor with lower dependence and abuse potential. An inverse agonist is an agent that binds to the same receptor binding-site as an agonist for that receptor and inhibits the constitutive activity of the receptor. Inverse agonists exert the opposite pharmacological effect of a receptor agonist, not merely an absence of the agonist effect as seen with antagonist. An example is the cannabinoid inverse agonist rimonabant. A co-agonist works with other co-agonists to produce the desired effect together. NMDA receptor activation requires the binding of both glutamate, glycine and D-serine co-agonists. An irreversible agonist is a type of agonist that binds permanently to a receptor through the formation of covalent bonds. A few of these have been described. A selective agonist is selective for a specific type of receptor. E.g. buspirone is a selective agonist for serotonin 5-HT1A. New findings that broaden the conventional definition of pharmacology demonstrate that ligands can concurrently behave as agonist ''and'' antagonists at the same receptor, depending on effector pathways or tissue type. Terms that describe this phenomenon are "functional selectivity", "protean agonism", or selective receptor modulators. == Activity == 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Agonist」の詳細全文を読む スポンサード リンク
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