A brief contact of native whole blood with adenosine diphosphate (ADP) promotes the release of the contents of platelet alpha granules but not dense bodies and increases platelet retention to glass bead columns.

We have previously demonstrated that a brief contact of native whole blood with ADP, promotes a dose dependent release of the contents of platelet alpha granules. In the present study we have shown that in our system there is not a parallel release of the contents of platelet dense bodies as measured by the release of serotonin (5 HT). This early and partial platelet activation determines an increase in platelet retention in glass bead columns. After exactly 15 seconds of activation of native whole blood from 6 healthy volunteers with ADP, in fact, there was a significant fall in the platelet count following the flow of native whole blood across glass beads. A significant decrease (from x = 182,000 +/- 13,700 to x = 120,000 +/- 8,00/microliters p less than 0.001) was present when the blood was stimulated with 0.4 microM ADP final concentration. These results suggest that early, partial platelet activation by ADP could facilitate their possible adhesion to a suitable surface exposed along the vascular tree.