The use of tritium labeled compounds to develop gamma-emitting receptor-binding radiotracers

In an effort to evaluate receptor binding drugs for their potential as gamma labeled radiopharmaceuticals suitable for clinical heart scanning, in vivo data were compared with the results obtained from a theoretical model. The distribution of selected tritium-labeled, receptor-binding radiotracers was studied in animals to determine if the heart to blood ratios agree with those obtained using a theoretical model of receptor binding. In general, the in vivo studies agree with the theoretical model when the concentration of the radiotracer in the heart is due to specific receptor binding. The use of the theoretical model for a first approximation followed by in vivo biodistribution studies is an efficient strategy to select those few from among the large number of receptor binding compounds that will ultimately yield an efficacious radiopharmaceutical to study receptor changes in the intact human heart.