Posted by michael on January 20, 2000, at 19:12:26
In reply to Re: what the heck is a partial agonist?, posted by Adam on January 20, 2000, at 18:33:18
> > > My understanding is that a partial agonist is a drug that activates a receptor to less than the maximum extent. I don't know how to express this quantitatively, though. (Where's Adam when we need him! :-) I think that the partial agonists can behave as antagonists at high concentrations.
> > >
> > > Buspar is a partial agonist at 5-HT1a receptors and, I believe, a full antagonist at D2 receptors.
> >
> > Could someone rephrase the last sentance above, without using the words agonins & antagonist? What's the net effect on the serotonin & dopamine levels/availability?
> >
> > michael
>
> First, it's difficult for me to discuss this without using terms like "agonist" and "antagonist" so I'll try to define those terms:
>
> Agonist: A substance that binds/has affinity for a receptor (such as the serotonin 1A or "5-HT1A" receptor) that stimulates a response mediated by that receptor. It might just mimic the action of the natural ligand (i. e. serotonin binding its receptor) or have other effects not caused by the natural ligand (like LSD binding the serotonin receptor, perhaps?)
>
> Antagonist: Essentially the opposite of the agonist. It binds/has affinity for the receptor and blocks responses mediated by that receptor. A dopamine D1 antagonist, for instance, would bind the D1 receptor and prevent or inhibit neurotransmission mediated by this receptor via binding of the natural ligand (dopamine). The ability of such a substance to antagonise such signalling is related to its binding affinity, i. e. its kinetics of binding must be more favorable than the agonist (be it the natural ligand or maybe a drug) to block signalling.
>Thanks for the lesson! Is this what you said?
Both Agonists and Antogonists have the ability to bind to a particular type of receptor (HT-1a, D2, etc.)
The difference is in the effect/result of this binding to the receptor?
When a Serotonin Agonist binds to a particular type of receptor, the result is the same as what happens when real serotonin actually binds to that particular type of receptor. It mimics serotonin, and in effect "increases the availability of serotonin"?
Whereas a Serotonin Antagonist would bind to that same particular type of receptor, but would not trigger that event. And in binding to that receptor, reduces the number of receptors available to serotonin for binding, which would in this case, approximate reducing the "availability of serotonin"?
poster:michael
thread:19073
URL: http://www.dr-bob.org/babble/20000112/msgs/19292.html