EFFECTS OF AMLODIPINE ON PLATELET-AGGREGATION IN HYPERTENSIVE PATIENTS - A CONTROLLED EX-VIVO STUDY

Platelet hyperactivity has been demonstrated in patients with arterial hypertension and is associated with an increase in platelet cytosolic free calcium concentration. Calcium channel blockers have been shown to decrease platelet aggregation and inhibit the mobilisation of intraplatelet calcium induced by various aggregating agents. However, both platelet aggregation and intraplatelet calcium fluxes are affected only at drug concentrations in excess of those attained in vivo. Ex vivo investigations of the antiaggregatory effects of calcium channel blockers in healthy subjects and hypertensive patients have yielded inconsistent results. In the present investigation, the ex vivo effects of amlodipine on platelet aggregation were evaluated in a placebo-controlled crossover study in 10 WHO class 1 hypertensive patients. Treatment with amlodipine 10mg once daily for 8 days resulted in a significant decrease in arterial blood pressure, with the mean arterial pressure decreasing from 127 +/- 4mm Hg to 110 +/- 7mm Hg (p<0.001). During the 8-day period of amlodipine treatment, platelet aggregation in whole blood and platelet-rich plasma was not significantly altered in comparison with baseline or placebo. In our study, however, we did not measure any index of platelet activation in vivo, such as plasma beta-thromboglobulin or thromboxane B-2 generation, and the possibility that amlodipine might exert some antiplatelet effect in vivo cannot therefore be excluded.