Myocardial accumulation of a dopamine D2 receptor-binding radioligand, 2'-iodospiperone

125I-2'-iodospiperone (2'-ISP), which has a high and selective affinity for dopamine D2 receptors, produced a high myocardial accumulation of radioactivity in the early phase after intravenous injection into mice. A human scintigraphic study also showed that the myocardium was clearly visualized soon after intravenous injection of the tracer. Analysis of the myocardial homogenate obtained from mice showed that 125I-2'-ISP was metabolically stable and was taken up the myocardium in its intact form. Administration of spiperone significantly reduced the myocardial uptake of 125I-2'-ISP in mice. Treatment with haloperidol and (+) butaclamol, which have a high affinity for dopamine D2 receptors, also tended to reduce the myocardial uptake of radioactivity, while (-)-butaclamol, which has no affinity for dopamine D2 receptors, caused no change in uptake. These findings suggest that the myocardial accumulation of 2'-ISP occurred in association with dopamine D2 (DA2) receptors.