Platelet-activating effect of low-density lipoprotein and its reversal by isradipine.

The effect of the calcium antagonist isradipine on platelet aggregation (induced ex vivo by serotonin and low-density lipoprotein [LDL]) was studied in 17 nonsmoking patients with essential hypertension. Platelet aggregation was measured after a four-week placebo period, and after four and 12 weeks of treatment with isradipine. Both the serotonin-induced and the LDL plus serotonin-induced platelet aggregation were significantly decreased after four weeks of isradipine treatment compared with placebo. The amplifying effect of LDL on the serotonin-induced aggregation was significant both after placebo and after active treatment with isradipine. A further decrease in platelet aggregation induced by LDL plus serotonin was observed after 12 weeks of isradipine treatment so that no amplification of serotonin-induced aggregation by LDL could be detected. In conclusion, it appears that treatment with isradipine restores the impaired platelet response to serotonin and LDL in hypertensive patients. The inhibition of this response may represent a cellular mechanism of thrombovascular protection.