Agonists

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. Agonists activate receptors. ... Agonists activate receptors. ... Pharmacology (in Greek: pharmakon (φάρμακον) meaning drug, and lego (λέγω) to tell (about)) is the study of how drugs interact with living organisms to produce a change in function. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Look up Endogenous in Wiktionary, the free dictionary. ... It has been suggested that this article or section be merged with ligand. ... For other uses, see Hormone (disambiguation). ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ...

Types

Full agonists bind (have affinity for) and activate a receptor, displaying 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. In chemistry and biochemistry, a dissociation constant or an ionization constant is a specific type of equilibrium constant used for reversible reactions or processes. ... Efficacy is the ability to produce a desired amount of a desired effect. ... Isoproterenol hydrochloride (Medihaler-Iso®) is a beta adrenergic receptor agonist medication, used as an inhaled aerosol to treat asthma. ... Adrenaline redirects here. ... Epinephrine Norepinephrine The adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines. ... For other uses, see Endorphin (disambiguation). ... A diagram showing the CNS: 1. ...

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 ligands which display both agonistic and antagonistic effects - when both a full agonist and partial agonist are present, the partial agonist actually acts as a competitive antagonist, competing with the full agonist for receptor occupancy and producing a net decrease in the receptor activation observed with the full agonist alone.^[1] Buspirone (brand-names Ansial, Ansiced, Anxiron, Axoren, Bespar, BuSpar, Buspimen, Buspinol, Buspisal, Narol, Spitomin, Sorbon) is an anxiolytic agent and a serotonin receptor agonist belonging to the azaspirodecanedione class of compounds. ... Aripiprazole (produced by Otsuka Pharmaceutical Co,. Ltd. ... Buprenorphine, is an opioid drug with partial agonist and antagonist actions. ... Clozapine (sold as Clozaril®, Leponex®, Fazaclo®) was the first of the atypical antipsychotics to be developed. ... Efficacy is the ability to produce a desired amount of a desired effect. ... A competitive antagonist is a receptor antagonist which binds to a receptor but fails to activate it. ...

An inverse agonist is an agent which binds to the same receptor binding-site as an agonist for that receptor and reverses constitutive activity of receptors. Inverse agonists exert the opposite pharmacological effect of a receptor agonist. In pharmacology, an inverse agonist is an agent which binds to the same receptor binding-site as an agonist for that receptor but exerts the opposite pharmacological effect. ...

A co-agonist works with other co-agonists to produce the desired effect together. NMDA receptor activation requires the binding of both of its glutamate and glycine co-agonists. An antagonist blocks a receptor from activation by agonists. Clinically partial agonists can activate receptors to give a desired submaximal response when inadequate amounts of the endogenous ligand are present, or they can reduce the overstimulation of receptors when excess amounts of the endogenous ligand are present.^[2] Antagonists will block the binding of an agonist at a receptor molecule, inhibiting the signal produced by a receptor-agonist coupling. ...

A selective agonist is selective for one certain type of receptor. It can additionally be of any of the aforementioned types.

A physiological agonist is a substance that creates the same bodily responses, but does not bind to the same receptor.

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 Look up Endogenous in Wiktionary, the free dictionary. ... For other uses, see Hormone (disambiguation). ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... Exogenous (or exogeneous) (from the Greek words exo and gen, meaning outside and production) refers to an action or object coming from outside a system. ... This article does not cite any references or sources. ...

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".^[3][4] Recently, a novel theory called Functional Selectivity (also referred to in the literature as “agonist trafficking”, “biased agonism”, “differential engagement” and “protean agonism”) has been proposed to broaden conventional definitions of pharmacology. ...

Activity (EC₅₀)

Potency

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 producing physiologically similar effects. 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 Potency may refer to: Virility Lack of the above: Erectile dysfunction, Infertility or Effeminacy. ... The term half maximal effective concentration (EC50) refers to the concentration of a drug which induces a response halfway between the baseline and maximum. ... Efficacy is the ability to produce a desired amount of a desired effect. ...

Therapeutic index

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. This relationship, termed the therapeutic index, is defined as the ratio LD50:ED50. In general, the narrower this margin, the more likely it is that the drug will produce unwanted effects. The therapeutic index has many limitations, notably the fact that LD50 cannot be measured in humans and, when measured in animals, is a poor guide to the likelihood of unwanted effects in humans. Nevertheless, the therapeutic index emphasizes the importance of the margin of safety, as distinct from the potency, in determining the usefulness of a drug. The therapeutic index (also known as therapeutic ratio), is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxic effects. ... This article is about the toxicological term. ... In pharmacology an effective dose is the amount of drug that produces a therapeutic response in 50% of the people taking it. ...

Etymology

From the Greek αγωνιστής (agōnistēs), contestant; champion; rival < αγων (agōn), contest, combat; exertion, struggle < αγω (agō), I lead, lead towards, conduct; drive The Greek language (Greek Ελληνικά, IPA // – Hellenic) is an Indo-European language with a documented history of some 3,000 years. ...

See also

• Receptor theory
• Inverse agonist
• Receptor antagonist
• Excitatory postsynaptic potential
• Allosteric modulator
• Intrinsic activity
• Dose response curve

Receptor theory is a theory that explains the mechanism of receptor activation and describes models which seek to accurately explain drug affects. ... In pharmacology, an inverse agonist is an agent which binds to the same receptor binding-site as an agonist for that receptor but exerts the opposite pharmacological effect. ... Antagonists will block the binding of an agonist at a receptor molecule, inhibiting the signal produced by a receptor-agonist coupling. ... In neuroscience, an excitatory postsynaptic potential (EPSP) is a temporary increase in postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell. ... In biochemistry, allosteric regulation is the regulation of an enzyme or protein by binding an effector molecule at the proteins allosteric site (that is, a site other than the proteins active site). ... Efficacy is the ability to produce a desired amount of a desired effect. ... It has been suggested that effective dose be merged into this article or section. ...

References