Stimulatory effects of vascular prostaglandins on the antiaggregatory activities of pentoxifylline acetylsalicylic acid combinations in vitro.

Pentoxifylline, Acetylsalicylic acid (ASA) and particularly both drugs in combination are known as active platelet inhibitors in pharmacological models in vivo. However, rather high amounts of these drugs are necessary to demonstrate inhibitory effects on the aggregation of human platelets in vitro, where no vessel walls are present. Surprisingly, these weak effects could be enhanced by the addition of external prostaglandins (prostacyclin (PGI2) and prostaglandin E1 (PGE1] into the in vitro system. Ternary combinations consisting of pentoxifylline, ASA and PGI2 exhibited the most impressive synergistic effects. Thus our study highlights the contribution of prostaglandins, especially of the natural vascular platelet inhibitor PGI2, for the display of the antiaggregatory potency of such drug combinations.