Posted by Larry Hoover on January 20, 2004, at 9:20:29
In reply to inverse agonist,- partial agonist ??, posted by linkadge on January 18, 2004, at 9:25:27
> Does anyone here know what an 'inverse agonist' is, or what a 'partial agonist' is.
I'm typing briefly....broken arm. Inverse agonists bind to a receptor for a known agonist, but incite an inverse reaction. An example is beta-carboline, which binds to the GABA receptor, but induces anxiety and increases risk of seizure.
Partial agonists also bind to the receptor, but induce a response quantifiably lower than that of a full agonist. E.g. niacinamide on the GABA receptor.
In both cases, the "interfering" substance will also exhibit some effects due to antagonism, because the receptors generally cannot interface with the natural ligand while these substances are bound (competitive inhibition).
To determine these fine distinctions, you need also to understand the two-state model of receptor conformation, and that some receptors (e.g. GABA) are partially on, even in the absence of the ligand. There are likely to be genetic and environmental factors influencing the balance between the two receptor states, apart from substances binding to them, which may account for the variability in response to receptor-binding drugs.
More:
http://www.umu.se/pharm-neuro/inst/UmePharmacodynamics.pdf
http://www.anaesthetist.com/physiol/basics/receptor/receptor.htmLar
poster:Larry Hoover
thread:302265
URL: http://www.dr-bob.org/babble/20040118/msgs/303171.html