SUBACUTE INFUSION OF PHYSIOLOGICAL DOSES OF PARATHYROID-HORMONE RAISES BLOOD-PRESSURE IN HUMANS

Background. Acute administration of parathyroid hormone (PTH) causes v asodilation and blood pressure decrease in experimental animals. This effect contrasts with the putative role of secondary hyperparathyroidi sm in the pathogenesis of hypertension of patients with renal failure. Uraemia is characterized by insulin resistance and hyperinsulinaemia. We therefore investigated whether subacute administration of physiolo gical doses of human 1,34-PTH affects blood pressure under conditions of controlled insulin levels (euglycaemic clamp technique) in humans. Methods. In a double-blind cross-over design 10 healthy male subjects received, on two occasions, in random order, for 2 h, either a sham in fusion or an infusion of 200 units of 1,34-PTH. Results. Mean ionized calcium concentration increased significantly (P < 0.01) within the no rmal range during euglycaemic hyperinsulinaemia, both with sham infusi on (from 1.25 +/- 0.04 to 1.29 +/- 0.02 mmol/l) and with infusion of 1 ,34-PTH, but the increase was more marked With 1,34-PTH administration (from 1.26 +/- 0.05 to 1.33 +/- 0.07). In addition, mean platelet int racellular calcium concentration (by fluorescence spectroscopy) was un changed with sham infusion (49.9 +/- 4.1 versus 50.3 +/- 5.0 nmol), bu t increased significantly (P < 0.05; paired t-test) after 1,34-PTH inf usion (from 49.8 +/- 5.0 to 52.8 +/- 5.8). The infusion of 1,34-PTH re sulted in a significant (P < 0.01) increase in mean MAP (from 84 +/- 5 to gs +/- 5 mmHg) as compared with sham infusion (85 +/- 4 versus 86 +/- 4). The intra-individual changes in intracellular calcium concentr ation (Delta[Ca2+](i)) were significantly correlated to the changes in mean MAP (Delta MAP) (r = 0.87, P < 0.001). In contrast to blood pres sure, insulin sensitivity was not affected by 1,34-PTH infusion (M-val ue: 7.2 +/- 1.6 mg/kg per min) as compared with sham infusion (7.3 +/- 1.4). Conclusion. Subacute administration of physiological doses of p arathyroid hormone under hyperinsulinaemic conditions significantly af fects intracellular calcium and blood pressure in healthy subjects, bu t does not affect the action of insulin.