PHARMACOLOGICAL CHARACTERIZATION AND AUTORADIOGRAPHIC LOCALIZATION OF DOPAMINE-RECEPTORS IN THE HUMAN ADRENAL-CORTEX

The pharmacological characteristics and the anatomical localization of dopamine D-1-like and D-2-like receptors were studied in sections of the human adrenal cortex using radioligand binding and autoradiographic techniques. [H-3]SCH 23390 was used as a ligand of D-1-like receptors, whereas [H-3]spiroperidol was used to label D-2-like receptors. No specific [H-3]SCH 23390 binding was detectable in sections of the human adrenal cortex. On the other hand, [H-3]spiroperidol was bound to sections of the adrenal gland in a manner consistent with the labelling of dopamine D-2-like receptor sites. The binding was time, temperature and concentration dependent, belonging in the range of concentrations of the radioligand used for a single class of high-affinity sites. The dissociation constant (K-d) averaged 2.7 nmol/l, whereas the maximum density of binding sites (B-max) was 160 nmol/mg tissue. Experiments on the pharmacological specificity of [H-3]spiroperidol binding to sections of the human adrenal cortex revealed that clozapine was the most powerful displacer of [H-3]spiroperidol from sections of the human adrenal cortex. This suggests the presence in the human adrenal cortex of dopamine receptors of the D-4 subtype. Light microscope autoradiography showed the highest density of specific [H-3]spiroperidol binding sites in the zona glomerulosa and to a lesser extent in the zona reticularis. Only sparse [H-3]spiroperidol binding sites were localized in the zona fasciculata. The possible functional consequences of this localization of dopamine D-2-like receptor sites in the human adrenal cortex are discussed.