Influence of cardiovascular drugs on platelet aggregation

All vasodilatory drugs reported in this chapter possess an antiaggregatory effect on platelets, some of them with a synergistic effect on prostacyclin-induced inhibition of aggregation. Thus, the question seems valid whether the antiaggregatory effect represents one part of their antianginal and antihypertensive action. Some vasodilators stimulate the biosynthesis of prostacyclin and/or other vasodilating prostaglandins. This stimulation could be linked not only to the antiaggregatory but also to the vasodilating action. The influence on prostaglandin biosynthesis, however, is not obligatory for all vasodilators, as nitroglycerin proves. Trapidil inhibits the biosynthesis and the effect of thromboxane A2, as our own experiments and those by Ohnishi et al. (7) have shown. This effect could be favorable in patients with heart infarction. Lefer et al. (5) have demonstrated a fivefold increase in thromboxane release after experimental ligation of the coronary artery in the cat. Pinane thromboxane, a thromboxane antagonist, almost completely abolished all deleterious consequences of ischemia. Whether trapidil is also able to inhibit thromboxane biosynthesis and activity under clinical conditions of heart infarction will be the topic of further investigations.