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Agonist: Difference between revisions
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[[File:Efficacy spectrum.png|thumbnail|275px|Efficacy spectrum of receptor ligands]] | [[File:Efficacy spectrum.png|thumbnail|275px|Efficacy spectrum of receptor ligands]] | ||
[[File:Inverse_agonist_3.svg|thumbnail|275px|Dose response curves of receptor ligands]] | [[File:Inverse_agonist_3.svg|thumbnail|275px|Dose response curves of receptor ligands]] | ||
An '''agonist''' is a chemical that binds to the [[receptor]] of a cell and activates the receptor to cause a physiological response. An agonist initiates the same reaction typically produced by the binding of an endogenous ligand (such as a hormone or neurotransmitter) with a receptor.<ref> | An '''agonist''' is a chemical that binds to the [[receptor]] of a cell and activates the receptor to cause a physiological response. An agonist initiates the same reaction typically produced by the binding of an endogenous ligand (such as a hormone or neurotransmitter) with a receptor.<ref>{{Citation | title=Definition of AGONIST | url=https://www.merriam-webster.com/dictionary/agonist}}</ref> A substance's ability to affect a given receptor is dependent on the substance's affinity and intrinsic efficacy towards that receptor. The affinity of a substance describes the strength of attraction between it and a given receptor, and consequently its ability to bind to that receptor. A substance with a high affinity for a receptor has a high likelihood of binding to it, while a substance with a low affinity has a lesser degree of attraction towards a receptor. | ||
This contrasts the efficacy of a | This contrasts the efficacy of a substance, which describes a substance's capacity to produce a response when bound to a receptor. A substance with high efficacy will produce a proportionally stronger effect than a substance of lower efficacy occupying the same number of receptors. The maximum efficacy of a substance reflects the greatest attainable response to a particular substance on a receptor set regardless of dose. A substance with a high efficacy may need to occupy fewer receptors to produce maximum effects, meaning it will not produce stronger effects beyond a certain dosage. | ||
In contrast to an agonist, an [[antagonist]] is a chemical that binds to the receptor of a cell without causing a physiological response. Receptor antagonists work by blocking or diminishing the effects produced by endogenous or | In contrast to an agonist, an [[antagonist]] is a chemical that binds to the receptor of a cell without causing a physiological response. Receptor antagonists work by blocking or diminishing the effects produced by endogenous or substance-induced agonism of a receptor. | ||
==Types of | ==Types of agonists== | ||
[[Receptors]] can be activated by chemicals produced by the body (endogenous) or chemicals from outside of the body (exogenous). Therefore, an endogenous agonist for a particular receptor is a chemical produced in the body that binds to and activates that receptor. For example, [[serotonin]] is the endogenous agonist of serotonin receptors. | [[Receptors]] can be activated by chemicals produced by the body (endogenous) or chemicals from outside of the body (exogenous). Therefore, an endogenous agonist for a particular receptor is a chemical produced in the body that binds to and activates that receptor. For example, [[serotonin]] is the endogenous agonist of serotonin receptors. | ||
===Agonists=== | ===Agonists=== | ||
There are several types of agonist: | There are several types of agonist: | ||
*A '''superagonist''' is an agonist that produces a greater effect from the receptor than the endogenous agonist, and therefore has an efficacy of over 100%. | *A '''superagonist''' is an agonist that produces a greater effect from the receptor than the endogenous agonist, and therefore has an efficacy of over 100%. | ||
*A '''full agonist''' binds and activates a receptor with an efficacy equal to the endogenous agonist. For example, [[heroin]] mimics the action of endorphins on μ-opioid receptors in the nervous system. | *A '''full agonist''' binds and activates a receptor with an efficacy equal to the endogenous agonist. For example, [[heroin]] mimics the action of endorphins on μ-opioid receptors in the nervous system. | ||
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===Allosteric modulators=== | ===Allosteric modulators=== | ||
An allosteric modulator is a substance which indirectly influences (modulates) the effects of an agonist or inverse agonist at a target protein (for example, a receptor). Allosteric modulators bind to a site distinct from that of the agonist binding site. Usually they induce a change within the protein structure. A positive allosteric modulator induces an amplification, while a negative modulator induces an attenuation of the effects of the ligand without triggering a functional activity on its own in the absence of the ligand. | An allosteric modulator is a substance which indirectly influences (modulates) the effects of an agonist or inverse agonist at a target protein (for example, a receptor). Allosteric modulators bind to a site distinct from that of the agonist binding site. Usually they induce a change within the protein structure. A positive allosteric modulator induces an amplification, while a negative modulator induces an attenuation of the effects of the ligand without triggering a functional activity on its own in the absence of the ligand. | ||
===Partial agonists=== | |||
A partial agonist is a substance that activates a receptor but only has partial efficacy in comparison to a full agonist. As a result, partial agonists may have unique properties that full agonists or inverse agonists lack. Some partial agonists, such as [[buprenorphine]], have a ceiling effect, where the subjective effects of the substance do not get any stronger past a certain dose. Partial agonists may also behave as an antagonist in the presence of a full agonist. Buprenorphine, a partial agonist of the μ-opioid receptor, behaves as an antagonist in the presence of other opioids such as [[heroin]]. An individual who is dependent on opioids will go into withdrawal if they take buprenorphine while opioids are still in their system due to buprenorphine's antagonistic effects. | |||
==See also== | ==See also== | ||
*[[Responsible use]] | *[[Responsible use]] | ||
*[[Scientific information]] | *[[Scientific information]] | ||
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==External links== | ==External links== | ||
*[https://en.wikipedia.org/wiki/Agonist Agonist (Wikipedia)] | *[https://en.wikipedia.org/wiki/Agonist Agonist (Wikipedia)] | ||
==References== | ==References== | ||
<references/> | <references /> | ||
[[Category:Pharmacology]] | |||
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