Dopamine D2 receptor gene expression and binding sites in adrenal medulla and pheochromocytoma

To determine whether dopamine D2 receptors are present in normal and neoplastic chromaffin tissues, 10 pheochromocytomas and 5 human adrenal glands were studied. Dopamine D2 receptor messenger ribonucleic acid corresponding to a single band of approximately 2.5 kilobases was detected in both pheochromocytoma and human adrenal gland by Northern blot analysis. D2 receptor messenger ribonucleic acid levels determined by dot blot analysis were 3.1-fold lower in human adrenal medullas than in pheochromocytomas (P < 0.001). Simultaneous Scatchard analysis of [3H]spiperone binding experiments demonstrated the presence of two different binding sites in membrane preparations from bovine adrenal medullas [R1: Kd = 0.14 nmol/L; binding capacity (Bmax) = 6.2 fmol/mg protein: R2: Kd = 16 nmol/L; Bmax = 223 fmol/mg protein]. Similarly, two binding sites were present in membrane preparations from pheochromocytomas (R1: Kd = 0.39 nmol/L; R2: Kd = 61 nmol/L]. Binding capacities were greatly variable among pheochromocytomas (R1: Bmax = 12.0-372.5 fmol/mg protein; R2: Bmax = 1,000-11,586 fmol/mg protein). The relative potencies of different compounds to displace [3H]spiperone were spiperone > domperidone > (+)-butaclamol > quinpirole > SCH 23390 in bovine adrenal medulla, and spiperone >> domperidone > quinpirole > (+)-butaclamol > SCH 23390 in pheochromocytoma. We conclude that dopamine D2 receptors are synthesized in human adrenal medulla and pheochromocytoma tissues.