The synthetic amino terminal fragment of parathyroid hormone, PTH-(1-34), is a potent coronary artery vasodilator in the dog. In the present study, using instrumented open-chest dogs, we have performed the initial characterization of this effect and showed other dose-related cardiovascular effects of the hormone. A near-maximal flow response was obtained after intracoronary injection of 0.024 nmol X kg-1 PTH-(1-34) with minor, if any, concomitant changes in mean blood pressure, contractile force, or heart rate. At higher doses, mean blood pressure decreased while contractile force and heart rate increased in dose-dependent fashion. Infusion of PTH-(1-34) for 20 min showed that the vasodilatory effect could be sustained without a concomitant decrease in mean arterial pressure. Pharmacological characterization showed for the first time that the coronary response to PTH-(1-34) was unaltered in the presence of beta- or alpha-adrenergic, muscarinic, or histaminergic blockades. We conclude that PTH-(1-34), an endogenous circulating calcemic peptide, produces a large increase in coronary blood flow at doses sufficiently low to preclude complicating effects on blood pressure, contractile force, and heart rate. Furthermore, the results suggest that the vasodilatory effects may be specific.

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