Autoradiographic localization of dopamine DA-2 receptor sites in rat mesenteric vascular tree.
By using combined in vitro radioreceptor binding and autoradiographic techniques and [3H]spiroperidol (in the presence of the 5-hydroxytryptamine-2 receptor blocker ketanserin) as a ligand, the pharmacological properties and the anatomical localization of dopamine (DA) DA-2 receptors sites in rat mesenteric vascular tree were analyzed. [3H]Spiroperidol was bound by sections of rat mesentery in a manner consistent with the labeling of DA-2 receptors, with a Kd value of 2.48 nM and with a maximum binding value of 159 fmol/mg of protein. Light microscopic autoradiography revealed specific [3H]spiroperidol binding sites primarily in the adventitial layer and in the adventitial-medial border as well as in the intimal layer. Adventitial and adventitial-medial binding sites disappeared after 6-hydroxydopamine sympathectomy. In contrast, chemical sympathectomy was without effect on intimal [3H]spiroperidol binding sites. The density of adventitial and adventitial-medial binding sites was higher in medium and small sized vessels than in larger ones. These findings are indicative of the existence of DA-2 receptors sites located both prejunctionally (6-hydroxydopamine-sensitive) and in the intimal layer. Prejunctional mesenteric DA-2 receptors may be involved in the inhibition of noradrenaline release from sympathetic neuroeffector junctions. The functional significance of intimal [3H]spiroperidol binding sites, if any, should be established in future studies.
Ricci
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Dipartimento di Scienze Neurologiche, Università La Sapienza, Roma, Italy.
Amenta
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F
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D006892:Hydroxydopamines / Q000494:pharmacology; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism*; D016627:Oxidopamine; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000378:metabolism*; D017448:Receptors, Dopamine D2; D013134:Spiperone / Q000378:metabolism*; D013562:Sympathectomy
D006892:Hydroxydopamines; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D013134:Spiperone; D016627:Oxidopamine; D007650:Ketanserin