DENSITY AND DISTRIBUTION OF DOPAMINE-RECEPTORS IN THE CARDIOVASCULAR-SYSTEM AND IN THE KIDNEY

1 The pharmacological characteristics and the anatomical localization of dopamine (DA) DA-1 and DA-2 receptor sites were analysed in sections of rat heart, kidney, cerebral, mesenteric and caudal arteries. Moreover, DA-1 receptors were characterized in sections of human kidney. 2 [H-3]-SCH 23390, used as a ligand of DA-1 receptors, was specifically bound to sections of cerebral and mesenteric arteries and to both rat and human kidney. Negligible amounts of specific binding were noticeable in the heart and in the caudal artery. The binding was consistent with the labelling of DA-1 sites. In rat tissues binding was not sensitive to 6-hydroxydopamine (6-OHDA) sympathectomy. 3 Anatomically [H-3]-SCH 23390 was bound by the medial layer of cerebral, mesenteric and renal arteries. In the renal cortex, where occurred the highest accumulation of [H-3]-SCH 23390 binding sites, the ligand was bound primarily by proximal convoluted cortical tubules and juxtaglomerular cells. Comparatively, the human kidney was richer in tubular binding sites than the rat kidney. The opposite is true for vascular sites. 4 [H-3]-spiroperidol was used as a ligand of DA-2 receptors. To the incubation medium containing the ligand, appropriate concentrations of ketanserin were added to block the possible binding to 5-HT-2 sites. [H-3]-spiroperidol was bound by sections of the structures examined in a manner consistent with the labelling of DA-2 sites. 6-OHDA caused a significant reduction in the density of cardiac and vascular [H-3]-spiroperidol binding sites. 5 In the heart [H-3]-spiroperidol was bound primarily by atria (6-OHDA sensitive binding). At the arterial level, the ligand was bound primarily by a 6-OHDA sensitive site localized in the adventitia-media border as well as by an intimal 6-OHDA insensitive site. In the kidney [H-3]-spiroperidol was bound by cortical convoluted tubules and by medullary collecting tubules.