Parathyroid hormone responses to the dopaminergic agonist 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene

Plasma parathyroid hormone (PTH) responses to the dopaminergic agonist 2-amino-6,7-(OH)2-1,2,3,4-tetrahydronaphthalene (ADTN) have been studied in cattle. During ADTN infusions PTH increased within min in a dose-dependent manner, while calcium remained unchanged. Prolonged administration of ADTN caused transient PTH responses and crosstachyphylaxis to the subsequent administration of the beta-adrenergic agonist isoproterenol, but not to hypocalcemia, caused by infusions of ethylene-glycol-bis (beta-aminoethylether)-N,N'-tetraacetate. PTH responses were not modified by the beta-adrenergic blocking agent propranolol, infused in amounts earlier shown to suppress PTH responses to isoproterenol and epinephrine. In conclusion, the dopaminergic agonist ADTN caused a direct and transient stimulation of PTH secretion, not mediated by hypocalcemia or by beta-adrenergic receptors on parathyroid cells. However, crosstachyphylaxis to isoproterenol, but not to hypocalcemia, was observed.