Effects of parathyroid hormone on blood flow in different regional circulations

Parathyroid hormone and, in particular, its 1-34 aminoterminal fragment, PTH-(1-34), are potent vasodilators of the coronary circulation. In addition the hormone exerts a powerful hypotensive effect in a variety of animals, suggesting that the polypeptide hormone is vasoactive in peripheral regional circulations as well. The purpose of this study was to determine the regional circulations that were responsive and the relative sensitivity of each to the vasoactive properties of the hormone fragment. An anesthetized instrumented open-chest and/or open-abdomen dog model was used. Blood flow was continuously monitored in left circumflex, left pulmonary, right renal, celiac, and superior mesenteric arteries. Doses of synthetic human PTH-(1-34) ranging from 0.00024 to 0.24 nmol/kg were administered by bolus intra-arterial injections. Although PTH-(1-34) produced a dose-related vasodilation in each of the above regional vascular beds, marked differences in sensitivity were observed. The peptide elicited large increases in coronary (178%) and celiac (162%) blood flow. Maximal renal and pulmonary responses were relatively small (increases of 30 and 23%, respectively). Compared with control values, blood flow in the superior mesenteric circulation increased only at the highest dose tested. Thus sensitivity to the vascular effects of the hormone fragment differs markedly between the regional vascular beds of the dog.