Replies to post #175825 on Anavex Life Sciences Corp (AVXL)

[Steady_T]

Agonists are not binary, which as I understand what you are saying is how you characterize them. Agonists can vary from very strong to very weak.

So describing all SR1 agonists as being equal is not appropriate.

Also there are different mechanisms that can result in agonism. At this point I don't think it is exactly known what mechanism applies to 2-73 agonism of the SR1 receptor.

From Wikipedia.

Agonists versus antagonists
Efficacy spectrum of receptor ligands.

Not every ligand that binds to a receptor also activates that receptor. The following classes of ligands exist:

(Full) agonists are able to activate the receptor and result in a strong biological response. The natural endogenous ligand with the greatest efficacy for a given receptor is by definition a full agonist (100% efficacy).
Partial agonists do not activate receptors with maximal efficacy, even with maximal binding, causing partial responses compared to those of full agonists (efficacy between 0 and 100%).
Antagonists bind to receptors but do not activate them. This results in a receptor blockade, inhibiting the binding of agonists and inverse agonists. Receptor antagonists can be competitive (or reversible), and compete with the agonist for the receptor, or they can be irreversible antagonists that form covalent bonds (or extremely high affinity non-covalent bonds) with the receptor and completely block it. The proton pump inhibitor omeprazole is an example of an irreversible antagonist. The effects of irreversible antagonism can only be reversed by synthesis of new receptors.
Inverse agonists reduce the activity of receptors by inhibiting their constitutive activity (negative efficacy).
Allosteric modulators: They do not bind to the agonist-binding site of the receptor but instead on specific allosteric binding sites, through which they modify the effect of the agonist. For example, benzodiazepines (BZDs) bind to the BZD site on the GABAA receptor and potentiate the effect of endogenous GABA.

Note that the idea of receptor agonism and antagonism only refers to the interaction between receptors and ligands and not to their biological effects.