Inverse agonist

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Dose response curves of a full agonist, partial agonist, neutral antagonist and inverse agonist

In the field of pharmacology, an inverse agonist is an agent that binds to the same receptor as an agonist but induces a pharmacological response opposite to that agonist.

A prerequisite for an inverse agonist response is that the receptor must have a constitutive (also known as intrinsic or basal) level activity in the absence of any ligand. An agonist increases the activity of a receptor above its basal level, whereas an inverse agonist decreases the activity below the basal level. A neutral antagonist has no activity in the absence of an agonist or inverse agonist but can block the activity of either.[1]

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.

Examples

An example of a receptor that possesses basal activity and for which inverse agonists have been identified is the GABAA receptor. Agonists for the GABAA receptor (such as the benzodiazepines alprazolam and diazepam) elicit a sedative effect, whereas inverse agonists have anxiogenic (for example, Ro15-4513) or even convulsive effects (certain beta-carbolines).[2][3]

Two known endogenous inverse agonists are the Agouti-related peptide (AgRP) and its associated peptide Agouti signaling peptide (ASIP). Both are expressed in humans, and each binds melanocortin receptors 4 and 1 (Mc4R and Mc1R), respectively, with nanomolar affinities.[4]

References

  1. Kenakin T (2004). "Principles: receptor theory in pharmacology". Trends Pharmacol. Sci. 25 (4): 186–92. doi:10.1016/j.tips.2004.02.012. PMID 15063082.
  2. Mehta AK, Ticku MK (1988). "Ethanol potentiation of GABAergic transmission in cultured spinal cord neurons involves gamma-aminobutyric acidA-gated chloride channels". J. Pharmacol. Exp. Ther. 246 (2): 558–64. PMID 2457076.
  3. Sieghart W (1994). "Pharmacology of benzodiazepine receptors: an update". J Psychiatry Neurosci. 19 (1): 24–9. PMC 1188559. PMID 8148363.
  4. Ollmann MM, Lamoreux ML, Wilson BD, Barsh GS (February 1998). "Interaction of Agouti protein with the melanocortin 1 receptor in vitro and in vivo". Genes Dev. 12 (3): 316–30. doi:10.1101/gad.12.3.316. PMC 316484. PMID 9450927.CS1 maint: multiple names: authors list (link)
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