ABSTRACT
A radioligand is a ligand made radioactive by isotopic labeling and used as a probe to study the receptor of interest. The chemical structure of the molecule chosen for isotopic labeling is identical or similar to that of the endogenous ligand for the relevant receptor. Synthetic agonists and antagonists of the endogenous ligands that do not naturally exist can also be used as radioactive probes. The chemical structure of the ligand that can be isotopically labeled is one of the following:
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Ligands used for isotopic labeling are produced by chemical synthesis (i.e., purified, naturally occurring ligands are currently not used).
