Correlation of platelet calcium with blood pressure. Effect of antihypertensive therapy.

Intracellular free calcium has been implicated in vascular smooth-muscle contraction and in the pathophysiology of essential hypertension. We studied free-calcium levels in blood platelets, which have many features in common with vascular smooth-muscle cells. With use of an intracellularly trapped fluorescent dye, the free-calcium concentration in platelets was found to be elevated in 9 patients with borderline hypertension and 45 patients with established essential hypertension, who were compared with 38 normotensive subjects. There was a close correlation between the free-calcium level and both systolic and diastolic blood pressure (n = 92; r = 0.883 for systolic pressure and 0.931 for diastolic pressure; P less than 0.001 for both). Antihypertensive treatment with calcium-entry blockers (n = 15), beta-adrenoceptor blockers (n = 12), or a diuretic (n = 6) resulted in a reduction in free calcium, and this correlated with the fall in blood pressure (P less than 0.001). The intracellular free-calcium concentration in platelets may be determined by the same humoral or pharmacologic factors that determine the height of blood pressure.