The Development of Radiotracers that Are Substrates for (Catecholamine) Uptake1 and Uptake2

Abstract

Drugs are often defined as substances administered for diagnostic, prophylactic, or therapeutic purposes. Most of the radioactive substances administered in the practice of nuclear medicine are used for the first purpose and form a large subclass of the class, diagnostic drugs. But the term diagnostic is too narrow, for other types of information may also be obtained with this class of drugs and the term informational drug seems preferable. Radiopharmaceuticals that permit external detection after administration to man are currently or potentially capable of providing four types of information: the status of a physiologic function (e.g., measurements of iodide uptake by the thyroid gland under various dietary conditions); the presence of an abnormality (e.g., the screening information commonly obtained with scintigrams of various organs); a precise diagnosis [e.g., the nature of a lesion causing hyperaldosteronism (Seabold et al., 1976; Freitas et al., 1979) through combined use of a radioactive and stable drug in a suppression test]; the effect of therapy (e.g., the monitoring of propranolol therapy by serial measurements of cardiac ejection fraction). The first two examples are related to one another but not identical. The third represents a refinement that, it is hoped, will be joined by more examples in the future as we become more adept at the combined use of stable and radioactive drugs. The fourth is a rather crude example of an informational function, monitoring of therapy, that is not yet well developed in nuclear medicine. It is unrealistic to expect each informational drug to provide all four types of information.