The Different Effects Of Aspirin On Experimental Arterial And Venous Thrombus Formation

The influence of aspirin on platelet aggregation has given rise to frequent use as an antithrombotic agent. The knowledge of an unfavorable alteration of the thromboxane/prostacyclin ratio in the vessel wall at high dosage may favor therapy with low dosages of aspirin.

In order to obtain further information on the most effective dosage of aspirin the antithrombotic effect of repeated and different doses of aspirin was investigated in a standardized experimental model in 120 rabbits. In a 1. group aspirin 100 mg/kg were given 30 min before producing thrombosis. In two further groups aspirin was administered 12 hours and additionally 30 min before beginning the experiment. These rabbits received repeatedly either 10 mg (2.group) or 100 mg/kg (3. group) two times. In a 4.series aspirin was given at 50 mg/kg per day during three days.

A paradoxical thrombogenic effect with an increase of venous and arterial thrombus growth could be seen after a single high dose of 100 mg/kg aspirin but not after an additional one. If applicated two times a thrombus size minor than under repeated low doses of 10 mg/kg aspirin has been observed in the arterial and venous system (p< 0.05).Additionally after repeated treatment with 50 mg/kg an antithrombotic effect could be seen.

According to our data the paradoxical effect of only a single or first high dose of aspirin has to be taken into account but cannot be observed after repeated doses. At a low dosage aspirin a paradoxical effect was seen later,after a second dose. Animal thrombosis experiments does not provide sufficient evidence to support antithrombotic therapy with low doses of aspirin.