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Results for agonist
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[Late Latin agōnista, contender, from Greek agōnistēs, from agōn, contest. See agony.]
1. an organ, gland, muscle, or nerve center that is so connected physiologically with another that the two function simultaneously in forwarding a given process, such as when two muscles pull on the same skeletal member and receive a nervous excitation at the same time. Antonym: antagonist. 2. a drug or other substance having a specific cellular affinity that produces a predictable response.
1. A muscle primarily responsible for a given movement. Some muscles are agonists for more than one action on two or more joints. The biceps brachii, for example, are agonists for elbow flexion, radioulnar supination, and several movements of the shoulder joint.
2. A drug that interacts positively with receptors to produce a response in a tissue or organ.
1. in physiology a muscle which in contracting to move a part is opposed by another muscle (the antagonist).
2. in pharmacology, a drug which has affinity for the cellular receptors of another drug or natural substance and which produces a physiological effect.
In pharmacology an agonist is a substance that binds to a specific receptor and triggers a response in the cell. It mimics the action of an endogenous ligand (such as hormone or neurotransmitter) that binds to the same receptor.
Full agonists bind (have affinity for) and activate a receptor, displaying full efficacy at that receptor.
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. They may also be considered as a ligand which displays both agonistic and antagonistic effects, as in the presence of an full agonist, a partial agonist actually acts as a competitive antagonist.[1] A co-agonist works with other co-agonists to produce the desired effect together. An antagonist blocks a receptor from activation by agonists.
Receptors can be activated or inactivated either by endogenous (such as hormones and neurotransmitters) or exogenous (such as drugs) agonists and antagonists, resulting in stimulating or inhibiting a biological response. To see how an agonist may activate a receptor see this link.
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. Terms that describe this phenomenon are "functional selectivity" or "protean agonism".[2][3]
The potency of an agonist is usually defined by its EC50 value. This can be calculated for a given agonist by determining the concentration of agonist needed to elicit half of the maximum biological response of the agonist. Elucidating an EC50 value is useful for comparing the potency of drugs with similar efficacies. The lower the EC50, the greater the potency of the agonist the lower the concentration of drug that is required to elicit the maximum biological response
From the Greek αγωνιστής (agōnistēs), contestant; champion; rival < αγων (agōn), contest, combat; exertion, struggle < αγω (agō), I lead, lead towards, conduct; drive
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
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| Sports Science and Medicine. The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Agonist". Read more |
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