Localisation of dopamine D 2-like receptors in pulmonary artery of the human and rabbit but not of the rat

Abstract

The present study was designed to investigate the presence of dopamine D 2-like receptor sites in the main trunk of the human, rabbit and rat pulmonary artery using combined radioligand binding and light microscope autoradiography techniques. [ 3H]Spiroperidol was used as a ligand. The presence and the localisation of the sympathetic neuroeffector plexus were also studied using catecholamine histofluorescence techniques. Radioligand binding experiments demonstrated the labelling of a population of dopamine D 2-like receptors in sections of human and rabbit pulmonary arteries by [ 3H]spiroperidol. No specific binding occurred in sections of the rat pulmonary artery. Light microscope autoradiography showed the development of specific silver grains within the tunica adventitia, including the adventitia-media border, of the human and rabbit pulmonary arteries. No specific silver grains were found in sections of the rat pulmonary artery. Studies on the pharmacological characterisation of [ 3H]spiroperidol binding sites in the human and rabbit pulmonary arteries showed that they are sensitive primarily to domperidone, haloperidol, (-)-sulpiride or bromocriptine, and to a lesser extent to n-propylnorapomorphine, quinpirole or clozapine displacement. This suggests that [ 3H]spiroperidol binding sites in the pulmonary artery probably belong to the dopamine D 2 receptor subtype. Catecholamine histofluorescence techniques revealed a rich plexus of fluorescent adventitial and adventitial-medial nerve fibres in the human and to a lesser extent in the rabbit pulmonary artery. Comparison of the localisation of dopamine D 2-like receptor sites and of the sympathetic neuroeffector plexus in the pulmonary artery, suggests a possible prejunctional localisation of these sites.