digplanet beta 1: Athena
Share digplanet:


Applied sciences






















For other meanings of "agonist" or "agonism", see agonist (disambiguation). For a primary fictional character in a work, see Protagonist and Antagonist.
Agonists activating hypothetical receptors.
Efficacy spectrum of receptor ligands.

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[edit]

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.[1]

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.[2][3]

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",[4][5] or selective receptor modulators.[6]



The potency of an agonist is inversely related to its EC50 value. The EC50 can be measured for a given agonist by determining the concentration of agonist needed to elicit half of the maximum biological response of the agonist. The EC50 value is useful for comparing the potency of drugs with similar efficacies producing physiologically similar effects. The smaller the EC50 value, the greater the potency of the agonist, the lower the concentration of drug that is required to elicit the maximum biological response.

Therapeutic index[edit]

When a drug is used therapeutically, it is important to understand the margin of safety that exists between the dose needed for the desired effect and the dose that produces unwanted and possibly dangerous side-effects (measured by the TD50, the dose that produces toxicity in 50% of individuals). This relationship, termed the therapeutic index, is defined as the ratio TD50:ED50. In general, the narrower this margin, the more likely it is that the drug will produce unwanted effects. The therapeutic index emphasizes the importance of the margin of safety, as distinct from the potency, in determining the usefulness of a drug.


From the Greek αγωνιστής (agōnistēs), contestant; champion; rival < αγων (agōn), contest, combat; exertion, struggle < αγω (agō), I lead, lead towards, conduct; drive

See also[edit]


  1. ^ Goodman and Gilman's Manual of Pharmacology and Therapeutics. (11th edition, 2008). p14. ISBN 0-07-144343-6
  2. ^ De Mey JGR, Compeer MG, Meens MJ (2009). "Endothelin-1, an Endogenous Irreversible Agonist in Search of an Allosteric Inhibitor". Mol Cell Pharmacol 1 (5): 246–257. 
  3. ^ Rosenbaum DM, Zhang C, Lyons JA, Holl R, Aragao D, Arlow DH, Rasmussen SG, Choi HJ, Devree BT, Sunahara RK, Chae PS, Gellman SH, Dror RO, Shaw DE, Weis WI, Caffrey M, Gmeiner P, Kobilka BK (January 2013). "Structure and function of an irreversible agonist-β(2) adrenoceptor complex". Nature 469 (7329): 236–40. doi:10.1038/nature09665. PMC 3074335. PMID 21228876. 
  4. ^ Kenakin T (March 2001). "Inverse, protean, and ligand-selective agonism: matters of receptor conformation". FASEB J. 15 (3): 598–611. doi:10.1096/fj.00-0438rev. PMID 11259378. 
  5. ^ Urban JD, Clarke WP, von Zastrow M, Nichols DE, Kobilka B, Weinstein H, et al. (January 2007). "Functional selectivity and classical concepts of quantitative pharmacology". J. Pharmacol. Exp. Ther. 320 (1): 1–13. doi:10.1124/jpet.106.104463. PMID 16803859. 
  6. ^ Smith CL, O'Malley BW (February 2004). "Coregulator function: a key to understanding tissue specificity of selective receptor modulators". Endocr. Rev. 25 (1): 45–71. doi:10.1210/er.2003-0023. PMID 14769827. 

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Agonist — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

916 news items


Mon, 01 Sep 2014 08:33:45 -0700

THE AGONIST will release its new album, "Eye Of Providence", on November 11 in North America (one day earlier internationally) via Century Media. The band's first CD with new vocalist Vicky Psarakis was recorded at The Grid studio in their hometown ...


Thu, 07 Aug 2014 15:57:42 -0700

Montreal, Quebec, Canada-based melodic death metallers THE AGONIST will release their new album, "Eye Of Providence", on November 11 in North America (one day earlier internationally) via Century Media. The band's first CD with new vocalist Vicky ...
Sat, 09 Aug 2014 04:22:52 -0700

On Tuesday The Agonist Reveals New Album Details was a top story. Here is the recap: (TeamRock Radio) Montreal metal outfit The Agonist have released more details about their forthcoming album Eye Of Providence. In a studio update, the band say ...
Tue, 05 Aug 2014 04:19:13 -0700

(TeamRock Radio) Montreal metal outfit The Agonist have released more details about their forthcoming album Eye Of Providence. In a studio update, the band say having new vocalist Vicky Psarakis on board isn't the only change to their sound, with ...
Odessa American
Sun, 31 Aug 2014 08:11:15 -0700

Bromocriptine (Cycloset): is a dopamine agonist also used with diet & exercise to lower blood sugar in adults with type 2 diabetes. Colesevelam (welchol): is a bile acid sequestrant indicated as an adjunct to diet and exercise to improve glycemic ...

Pulmonary Hypertension News

Pulmonary Hypertension News
Mon, 01 Sep 2014 04:48:45 -0700

AMBITION is a randomized, double blind, multicenter Phase 4 clinical trial testing the efficacy of Ambrisentan, an endothelin-receptor agonist (Gilead and GlaxoSmithKline) and Tadalafil, a phosphodiesterase-5 inhibitor (Lilly ICOS), both in combination ...


Fri, 29 Aug 2014 07:23:33 -0700

The phase 4 AMBITION trial is comparing the combination of an endothelin-receptor agonist (Ambrisentan, Gilead and GlaxoSmithKline) and a phosphodiesterase-5 inhibitor (Tadalafil, Lilly ICOS) with each drug alone in the treatment of pulmonary arterial ...

MedPage Today

MedPage Today
Fri, 29 Aug 2014 08:22:30 -0700

... use of pioglitazone and the risk of bladder cancer," said Tom Harris, who heads golbal regulatory affairs for Takeda, in the company statement. Pioglitazone is a thiazolidinedione that acts as an agonist for peroxisome proliferator-activated ...

Oops, we seem to be having trouble contacting Twitter

Talk About Agonist

You can talk about Agonist with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!