Effects of the calcium antagonist nifedipine on thromboxane B2 level and platelet aggregation in hypertensive patients.

The effects of a calcium antagonist nifedipine (Adalat) on platelet aggregation was examined in vitro and in vivo. In vitro examination: Platelet aggregation induced by adenosine disphosphate (ADP), epinephrine, collagen, arachidonate, and thrombin was all inhibited dose-dependently in the platelet-rich plasma prepared from the blood of healthy individuals by the addition of nifedipine to a final concentration of 5 or 10 micrograms/ml. In vivo examination: 20 patients with essential hypertension were treated with 30 mg/d of nifedipine for 8 weeks. Significant decreases in both systolic and diastolic pressures were observed 2 weeks after the beginning of the administration, and continued throughout the administration period. ADP-induced platelet aggregation decreased by 25% after 2 weeks, 36% after 4 weeks, and 44% after 8 weeks (p less than 0.05 for all decreases). Plasma thromboxane B2 level also decreased markedly from 217.3 +/- 91.7 pg/ml before the administration to 119.0 +/- 29.7 pg/ml (p less than 0.01) 2 weeks after, and 99.1 +/- 25.4 pg/ml (p less than 0.01) 8 weeks after the beginning of the administration, suggesting suppressed thromboxane A2 production.