PARATHYROID-HORMONE AND PLATELET CYTOSOLIC CALCIUM-CONCENTRATION IN ESSENTIAL-HYPERTENSION

To investigate the possible relationships between blood pressure, para thyroid hormone (PTH) and platelet cytosolic Ca2+ concentration ([Ca2](i)) in patients with essential hypertension, we studied 17 patients with this disease aged 48 +/- 2 years and 17 normotensive controls age d 44 +/- 3 years. Platelet [Ca2+](i) was measured by spectrofluorimetr y using the dye Fura-2 acetoxymethylester. Patients with essential hyp ertension displayed lower levels of serum ionized Ca2+ (0.99 +/- 0.03 versus 1.1 +/- 0.01 mmol/l, P < 0.05) and higher serum intact PTH leve ls (37 +/- 3 versus 26 +/- 2 pg/ml, P < 0.01) than the normotensive co ntrols. Although serum levels of intact PTH were significantly correla ted with mean arterial pressure (MAP) in the combined group of subject s (r = 0.42, P < 0.05), there was no correlation when each group was c onsidered separately. Resting platelet [Ca2+](i) was also higher in pa tients than in controls (57 +/- 3 versus 48 +/- 2 nmol/l, P < 0.005). When platelets were stimulated in vitro with thrombin, the increment i n [Ca2+](i) was also greater in patients than in controls in the prese nce of extracellular Ca2+ (264 +/- 24 versus 194 +/- 19 nmol/l, P < 0. 05) but not in its absence (123 +/- 12 versus 112 +/- 10 nmol/l). The thrombin-induced increment in [Ca2+](i) was correlated with MAP in the hypertensive patients (r = 0.64, P < 0.01) and in the combined group of subjects (r = 0.42, P < 0.05). There was no relationship between re sting or thrombin-induced [Ca2+](i) and serum PTH in either group of p atients or in the combined group of subjects. Furthermore, preincubati on of platelets in vitro with PTH had no effect neither on resting pla telet [Ca2+](i) or on thrombin-induced increments in [Ca2+](i), both i n the presence and in the absence of extracellular Ca2+ in either grou p of subjects. Therefore, despite platelet [Ca2+](i) and serum PTH see m to be related to blood pressure, it appears that PTH does not partic ipate directly in the elevated platelet [Ca2+](i) found in patients wi th,essential hypertension.