Comparison Of The Effects Of Aspirin In Humans Ex Vivo In Platelet-Rich Plasma And Whole Blood

Abstract

The effect of aspirin on human platelet function is usually assessed using platelet-rich plasma (PRP). Some preliminary results in vitro suggested that the effect of aspirin appears to be greater in PRP than whole blood. To explore this possibility further, a comparison of the effect of aspirin in humans ex vivo has been made taking measurements simultaneously in whole blood and PRP at 2 platelet concentrations. Blood samples (36ml) were drawn from 7 male volunteers after a light breakfast. Each took 300mg soluble aspirin and blood samples were drawn again 2 hours later. Blood was mixed with 0.1 volumes 129nM trisodium citrate. Some (30ml) was then centrifuged to prepare PRP and platelet -poor plasma (PPP) by standard techniques. Platelet concentration of some PRP was adjusted with PPP to equal that of the corresponding blood sample; the rest was adjusted to 350,000 per μl. Aggregation in response to collagen (Horm, Munich) was measured photometrically at 37°. Aggregation in 0.5ml aliquots of whole blood was measured after 4 min stirring with 154mM NaCl (control) or collagen at 37° as the fall in single platelet count determined using an Ultraflo- 100 whole blood platelet counter (Clay Adams). The concentrations of collagen producing a 50% maximal response (EC50) in PRP and blood were determined. Dose-ratios for each volunteer were calculated by dividing the EC50 obtained after aspirin by the corresponding value obtained before aspirin. The effect of aspirin was significantly (p<0.001) less in blood than PRP. Whether or not the results in whole blood more closely reflect the effect of aspirin in vivo remains to be determined.