Autoradiographic localization of dopamine D1-like receptors in the rabbit pulmonary circulation

The pharmacological characteristics and the anatomical localization of dopamine D1-like receptors were studied in sections of rabbit lung using [3H]SCH 23390 as a ligand. [3H]SCH 23390 was bound to sections of rabbit lung in a manner consistent with the labelling of dopamine D1-like receptors. The binding was time-, temperature-, and concentration-dependent belonging to a single class of high affinity sites. The dissociation constant value (Kd) was 2.05 nM, whereas the maximum density of binding sites (Bmax) averaged 85 +/- 4 fmol/mg tissue. The pharmacological profile of [3H]SCH 23390 binding to sections of rabbit lung is consistent with the labelling of dopamine D1 receptors. Light microscope autoradiography revealed the development of silver grains which correspond to [3H]SCH 23390 binding sites within the tunica intima and the tunica media of large intrapulmonary artery branches. The presence of silver grains was also observed in the tunica media, but not in the tunica intima of medium-sized pulmonary artery branches. No silver grains were observed in small-sized pulmonary artery branches or in the pulmonary veins. Dopamine D1-like receptors localized in the rabbit pulmonary circulation probably mediate vasodilatation. Further work is necessary to clarify the functional significance of the non-homogeneous distribution of dopamine D1-like receptor sites in the pulmonary circulation.