Cardiovascular effects of parathyroid hormone: A study in healthy subjectsand normotensive patients with mild primary hyperparathyroidism

The aim of the study was to evaluate: 1) the cardiovascular function and th e autonomic drive to the heart in patients affected by primary hyperparathy roidism (pHPT) with no evidence of renal and cardiovascular complications; 2) the cardiovascular effects of acute administration of PTH in normal subj ects. In 14 patients affected by mild asymptomatic pHPT echocardiographic a ssessment of cardiovascular function and of the mechanic properties of the brachial and carotid artery, heart rate variability and the dispersion of Q T interval were performed before and 6 months after successful surgery. Twe nty age-and sex-matched healthy subjects were included in the study. Five h ealthy volunteers underwent a single blind, placebo-controlled, random orde r, cross-over study with infusion of PTH (hPTH 1-34, 200 U in saline over 5 min) or placebo. Ecocardiographic assessment of cardiovascular function, h eart rate variability, and QT interval were performed between 20 and 25 min after the start of the infusion and repeated after 15 min of tilting at 60 degrees. In pHPT patients the echocardiographic parameters were normal; left ventric ular isovolumetric relaxation time was always in the normal range, but sign ificantly shorter than in control subjects, suggesting an increased sympath etic stimulation. Arterial diameters and thickness, blood pressure, and QT interval were not significantly different with respect to normal subjects a nd were unchanged 6 months after surgery. pHPT patients lacked the circadia n rhythm of the low frequency to high frequency ratio, suggesting an increa sed sympathetic drive to the heart at nighttime. In normal subjects there w ere no significant differences in basal echocardiographic measurements duri ng PTH infusion with respect to placebo and in the hemodynamic response to tilt. These results suggest that cardiovascular function is substantially normal in normotensive pHPT patients with mild hypercalcemia. A modulation of the adrenergic control of circulation seems to be associated with hypercalcemia and/or chronic PTH excess, but its biological relevance needs further inve stigations.