Comparison of in vitro platelet aggregation and its inhibition by three antithrombotic drugs between human and guinea pig.

Platelets of guinea pigs are frequently used to evaluate the effect of new antiplatelet agents. Although several studies have compared the platelet aggregation between humans and guinea pigs, but so far the information is still limited. In this study, we compare the inhibitory effect of aspirin, dipyridamole and pentoxifylline on the platelet aggregation induced by adenosine diphosphate (ADP), collagen, arachidonic acid and thrombin between humans and guinea pigs. The results for humans and guinea pigs were compared and analysed by two-way analysis of variance (ANOVA). Our results showed: 1. The trends wherein these three drugs suppressed collagen-induced platelet aggregation was very similar in humans and guinea pigs. 2. In ADP-induced aggregation, the trend of inhibition caused by the three drugs was also similar in humans and guinea pigs except that a difference in platelet disaggregation at a late phase of platelet aggregation was noted. 3. In arachidonic acid- and thrombin-induced aggregations, the trend of inhibition caused by the three drugs was somewhat different in humans and guinea pigs. 4. Considering all activators as a whole, it was found that the status of platelet disaggregation at the late phase of platelet aggregation was different in humans and guinea pigs. Therefore, we concluded that: 1. Collagen was the most appropriate platelet activator when we used platelets of guinea pigs to study the effect of new antiplatelet agents. 2. When platelets of guinea pigs were used to study platelet aggregation, no matter which activator was used, we should avoid using the late phase of aggregation as the control index for comparison, because the results thus obtained might not be applicable to human platelets.