Enhanced Risk of Thromboembolic Disease in Hypertension from Platelet Hyperfunction and Decreased Fibrinolytic Activity: Has Antihypertensive Therapy Any Influence?

Enhanced platelet function and a decrease in fibrinolytic activity have been reported in patients with mild hypertension after treatment with various nonselective β-blockers. Until now, such changes have not been reported during treatment with β1-selective drugs or with agents that have intrinsic sympathomimetic activity. The impact of angiotensin-converting enzyme inhibitors and diuretics on platelet function and fibrinolytic activity has not been fully elucidated. Calcium antagonists of various types, however, are known to decrease platelet release in vivo whereas their effects on platelet aggregation and fibrinolytic activity are less clear. The new dihydropy- ridine calcium antagonist isradipine, when tested in a group of patients with mild hypertension, resulted in a decrease in platelet aggregation, a shortened euglobulin clot-lysis time, and a dramatic increase in t-PA (tissue-plasminogen activator) activity after 14 days of treatment. These changes remained stable throughout the 1-year study period. The fact that antihypertensive therapy does not always result in the hoped-for prolongation of life, despite satisfactory blood pressure reduction, may be in part due to an unfavorable impact on various components of the blood-clotting system.