AGONISTS AND ANTAGONISTS

Agonists and antagonists can be prepared, which interact directly with the receptor. Both bind to the receptor but an agonist produces the biological effect of the hormone while the antagonist does not. Compounds can be prepared that block the metabolism or re-uptake of a neurotransmitter and thus its effect may persist. Other compounds may interfere either with the biosynthesis or regulatory mechanism. Finally, compounds can be prepared that target the ion-channels themselves or that alter the shape and accessibility of the receptor. Examples of these are discussed in the following sections.

If we consider the structures of the neurotransmitters it can be seen that they possess at least two potential binding functional groups separated by a flexible carbon chain. There are a number of different possible conformations in which the neurotransmitters can bind to the receptor. This can lead to there being sub-sets of the different receptors, one, for example, in which the neurotransmitter might bind in an extended conformation and another in which it is folded. These different receptors may be distinguished by using agonists, which possess a more rigid relationship between the binding groups such that they can bind to one sub-set and not to another. This idea of distinguishing between sub-sets of receptors by using structurally more rigid agonists can be extended to achieving selectivity in drugs that target specific receptors.