Light microscope autoradiography of peripheral dopamine receptor subtypes

Radioligand binding assay techniques associated with light microscope autoradiography were used for investigating the pharmacological profile and the micro anatomical localization of peripheral dopamine receptor subtypes. In systemic arteries, the predominant dopamine D-1-like receptor belongs to the D-5 (or D-1B) subtype. It is located within smooth muscle of the tunica media. In pulmonary arteries, dopamine D-1-like receptors have primarily an endothelial localization and belong to the dopamine D-1 (or D-1A) receptor subtype. Both systemic and pulmonary arteries express a dopamine D-2-like receptor, belonging to the D-2 receptor subtype. It has a prejunctional localization in the majority of vascular beds investigated. In cerebral, coronary and mesenteric arteries, it has also an endothelial localization. In the heart, a dopamine D-4 receptor was identified. It is expressed by atrial tissue and has a widespread distribution overall atrial musculature. The kidney expresses both dopamine D-1-like and D-2-like receptors. Renal dopamine D-1-like receptors have a vascular and tubular localization. The majority of these sites belongs to the D-5 receptor subtype. A smaller D-1 receptor population has primarily a tubular localization. Renal dopamine D-2-like receptors belong to the dopamine D-3 subtype and in lesser amounts to the D-2 Sind D-4 receptor subtypes. Renal dopamine D-3 receptor has to a greater extent a tubular localization, whereas the D-4 receptor is located within glomerular arterioles. The above results suggest that radioligand binding assay and autoradiographic techniques, if performed in the presence of compounds displaying specific receptor subtype selectivity, may contribute to characterize, mainly from a quantitative point of view, peripheral dopamine receptors.