Reduction in Single Platelets During Primary and Secondary Aggregation

Citrated platelet-rich plasma from nine individuals was tested at the threshold concentration of ADP (mean value, 2.44+ 0.85 pM) where two phases of aggregation were evident. Samples were withdrawn at intervals and mixed in 0.15 M NaCl containing 0.01 Vo glutaraldehyde to fix the state of aggregation. Single, unaggregated platelets were then estimated in a resistive-particle counter. For purposes of comparison, the maximum increase in transmission in each experiment was set at 1007o and changes expressed relative to this value. Aggregation is given as the per cent loss in single platelets relative to the preaggregation number. The temperature was 37" and values are presented as means plus and minus one standard deviation.