Does antihypertensive therapy affect the natural protection against thrombosis?

Fibrinolytic activity was measured in a 14-day placebo-controlled study of propranolol and the calcium antagonist isradipine in 20 mildly hypertensive patients (diastolic blood pressure 95-115 mm Hg) compared with 24 healthy volunteers. The parameters under study included euglobulin clot-lysis time, and tissue-plasminogen activator activity and its inhibitor (PAI). The two drugs exerted equal antihypertensive effects in the patients who had raised blood pressure, but had markedly different actions on the fibrinolytic system. Propranolol substantially reduced the fibrinolytic activity in both the hypertensive and healthy control groups. Isradipine, on the other hand, had no effect on fibrinolytic activity in the controls, but augmented the activity in the hypertensive subjects. The possible mechanisms for the different actions of the two agents may be related to the vascular endothelium.