Human blood anticoagulated with a serine protease inhibitor was centrifuged with an
erythrocyte agglutinating agent in the bottom of the tube. Platelet rich plasma (PRP)
obtained in this manner contained platelets with different ability to aggregate with
ADP located in the various layers of the tube. Platelets in the midportion of the
tube were most extensively aggregated by a standard dose of ADP (1.6 μM) and mechanical
stirring. Platelets in the lowest portion aggregated least, but still showed normal
“shape change” when they were stimulated. The uppermost platelets in the tube also
showed somewhat reduced aggregation compared with the midportion. These observations
could not be explained by differences in platelet concentrations. On a descriptive
basis the platelets in the midportion of the tube are designated preactivated and
the lowermost platelets deactivated.
Key words
Platelet aggregation - ADP - Refractory platelets - Platelet shape change
