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An agonist increases the activity of a receptor above its basal level, whereas an inverse agonist decreases the activity below the basal level. The efficacy of a full agonist is by definition 100%, a neutral antagonist has 0% efficacy, and an inverse agonist has < 0% (i.e., negative) efficacy.
A receptor modulator, or receptor ligand, is a general term for a substance, endogenous or exogenous, that binds to and regulates the activity of chemical receptors.They are ligands that can act on different parts of receptors and regulate activity in a positive, negative, or neutral direction with varying degrees of efficacy.
Over the last 40 years, a variety of drugs have been developed from non-selective alpha-1 receptor antagonists to selective alpha-1 antagonists and alpha-1 receptor inverse agonists. [2] [3] The first drug that was used was a non-selective alpha blocker, named phenoxybenzamine and was used to treat BPH. [2]
An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist.
[1] Orthosteric agonist (A) binds to orthosteric site (B) of a receptor (E). Allosteric modulator (C) binds to allosteric site (D). Modulator increases/lowers the affinity (1) and/or efficacy (2) of an agonist. Modulator may also act as an agonist and yield an agonistic effect (3). Modulated orthosteric agonist affects the receptor (4).
[4] [11] CB 1 antagonists produce inverse cannabimimetic effects that are opposite in direction from those produced by agonists for these receptors. [4] [16] CB 1 receptors are highly expressed in hypothalamic areas which are involved in central food intake control and feeding behavior. This strongly indicates that the cannabinoid system is ...
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Agonist vs. antagonist. In pharmacology the term agonist-antagonist or mixed agonist/antagonist is used to refer to a drug which under some conditions behaves as an agonist (a substance that fully activates the receptor that it binds to) while under other conditions, behaves as an antagonist (a substance that binds to a receptor but does not activate and can block the activity of other agonists).