Characterization of Dopaminergic Receptors in Dispersed Bovine Parathyroid Cells

Several dopaminergic ligands were assessed for their effects on cAMP accumulation, adenylate cyclase activity, and parathyroid hormone (PTH) release from dispersed bovine parathyroid cells. Dopamine, 6,7-dihydroxy-1,2,3,4 tetrahydronaphthalene (ADTN), 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF-38393), and apomorphine increased cAMP content 30-, 25-, 10-, and 2- to 3-fold with K a ’s of 0.6, 0.5, 1, and 1-3 µM, respectively. These same agents also stimulated adenylate cyclase activity up to 4-fold and PTH release 1.3- to 3-fold. With the exception of lisuride ( K i = 15 nM), ergot derivatives were of relatively low potency ( K i ’s = 0.4-20 µM) in inhibiting dopamine-stimulated cAMP accumulation. Similar K i ’s were observed for effects on dopamine-stimulated adenylate cyclase activity and PTH release. Interactions of these ligands with the dopamine receptor could be clearly differentiated from effects of β-adrenergic or α-adrenergic receptors also known to modulate cAMP accumulation and secretion in this cell type. These results demonstrate the presence of a D-1 dopaminergic receptor on bovine parathyroid cells and document further the relationship in this receptor subclass between adenylate cyclase activity, cAMP accumulation, and a biologic response.