[Erythrocytes modulate the anti-aggregation effect of aspirin and dipyridamole. Study under static conditions and in...

The modulating role played by red cells on platelet function is well known, yet its mechanism of action in the presence of antiaggregating agents is not clearly defined. We tried to assess the influence of aspirin (ASA) or dipyridamole (DIP) treated red cells on platelet aggregation in plasma, with the samples in static conditions and under flow in a perfusion system.

Platelet-rich plasma (PRP) was adjusted to 4 x 10(9)/L. Red cells were washed with a 0.9% sodium chloride and 5mM glucose solution, then resuspended in PRP until a 40% haematocrit was attained. The drugs were added separately or together and the mixture was incubated for 10 minutes at 37 degrees C. Three series of tests were carried out: a) with reconstituted blood; b) with red cells alone; c) with the red cells washed in a 10-fold volume so as to eliminate all the drugs. The samples were divided in two parts: one was let to rest and the other was circulated through a perfusion system with a peristaltic pump. Simultaneous tests with untreated red cells and PRP were run as control in each session. A multichannel aggregameter was used to assess platelet aggregation according to Born's turbidimetric method. Variance analysis (ANOVA) or Student's t test were used for the statistical evaluation.

Platelets attained from control samples under flow conditions showed partial inhibition of the maximal aggregation (58.02 +/- 9.92%). The inhibitory power of ASA was higher than that of DIP in all cases. Aggregation was totally inhibited by ASA from the beginning in treated whole blood, but the inhibitory effect appeared later when working with red cells alone, suggesting that red cells must retain part of the drug, which cannot exert its effect until it has been released after several minutes. The inhibition of platelet aggregation when working with washed treated red cells was more effective under flow conditions, chiefly with combined treatment with ASA+DIP.

These studies stress the importance of flow conditions in the red cells-platelets interaction and in the regulation of the therapeutic agents used to modify platelet function.