A novel radioiodinated high affinity ligand for the D2‐dopamine receptor

A novel high affinity dopaminergic ligand, N-(p-aminophenethyl)spiroperidol, has been synthesized and radioiodinated to a specific radioactivity of 2175 Ci/mmol. Binding of this ligand to bovine anterior pituitary membranes is: rapid (40-60 min to equilibrium at 25 degrees C) and reversible (t1/2 = 1 h at 25 degrees C); saturable and of high affinity (KD approximately 20 pM) and displays a typical D2-dopaminergic specificity. The ligand, which identifies the same number of receptor sites as other tritiated antagonist ligands, can be used in different tissues and preparations to delineate the characteristics of the D2 receptor. Thus, this high affinity, high specific radioactivity ligand (N-(p-amino-m-[125I]iodophenethyl)spiroperidol) represents a tool which until now had not been available for the characterization of the D2-dopamine receptor.