Localization of dopamine receptors in the rabbit lung vasculature

The localization of dopamine receptor subtypes in the rabbit pulmonary circulation was investigated by using combined radioligand binding and light microscope autoradiography techniques. Dopamine D1-like receptors, probably belonging to the dopamine D1 receptor subtype, were demonstrated in sections of rabbit lung using [3H]-SCH 23390 as a ligand. This site is located within the tunica intima and the tunica media of large intrapulmonary artery branches (diameter > 300 microns) as well as within the tunica media of medium-sized pulmonary artery branches (diameter between 100 and 300 microns). No [3H]-SCH 23390 binding sites were found in small-sized pulmonary artery branches (diameter < 100 microns) or in pulmonary veins. Dopamine D2-like receptors, probably belonging to the dopamine D2 receptor subtype, were demonstrated with radioligand binding techniques in sections of extrapulmonary arteries but not of lung using [3H]-spiroperidol as a ligand. Light microscope autoradiography revealed the localization of this site within the tunica adventitia of extrapulmonary arteries as well as of large- and medium-sized intrapulmonary artery branches. The different anatomical localization of dopamine D1- and D2-like receptors in the rabbit pulmonary vasculature suggests that these sites are involved in the modulation of pulmonary vascular tone by interacting with different receptors having endothelial, muscular and probably prejunctional localization. The functional significance of the uneven distribution of dopamine receptor subtypes throughout the pulmonary vascular bed should be clarified in future studies.