1. Blood pressure, left ventricular mass and platelet cytosolic free calcium concentrations were measured in 23 patients with untreated primary hyperparathyroidism, 30 normotensive control subjects and 23 control subjects matched for age, sex and blood pressure. In 12 patients measurements were repeated after parathyroidectomy.
2. Patients with primary hyperparathyroidism had significantly elevated blood pressures (139 ± 6/86 ± 3 mmHg, mean ± sem) compared with control subjects (125 ± 2/78 ± 1 mmHg), but high values persisted after hypercalcaemia was corrected.
3. Despite chronic extracellular hypercalcaemia, intracellular free calcium levels were lower in patients with hyperparathyroidism than in controls matched for age, sex and blood pressure (median concentrations 81.5 nmol/l vs 93 nmol/l, 95% confidence interval 0.1 to 20.1; P < 0.05) and values tended to increase after parathyroidectomy.
4. Left ventricular mass index was increased in the primary hyperparathyroid group as compared with control subjects matched for age, sex and blood pressure (123 g/m2 vs 100 g/m2, 95% confidence interval −36.1 to −3.1; P = 0.03). Parathyroidectomy resulted in a small reduction of the left ventricular mass index (123.5 g/m2 vs 104 g/m2, 95% confidence interval 46.5 to 2.5; P = 0.1) but no change in blood pressure.
5. Hypertension and left ventricular hypertrophy in primary hyperparathyroidism are associated with relatively low levels of free calcium in platelets.